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Memory coin 2 0 mining bitcoins

By now it has collected a few hundred transactions in the memory pool. Whatever transactions remain in the memory pool are unconfirmed and are waiting to be recorded in a new block. This block is called a candidate block because it is not yet a valid block, as it does not contain a valid proof of work.

The block becomes valid only if the miner succeeds in finding a solution to the proof-of-work algorithm. Prioritized transactions can be sent without any fees, if there is enough space in the block. The priority of a transaction is calculated as the sum of the value and age of the inputs divided by the total size of the transaction:.

The size of the transaction is measured in bytes. The first 50 kilobytes of transaction space in a block are set aside for high-priority transactions. This allows high-priority transactions to be processed even if they carry zero fees. Some miners choose to mine transactions without fees on a best-effort basis.

Other miners may choose to ignore transactions without fees. Any transactions left in the memory pool, after the block is filled, will remain in the pool for inclusion in the next block. Eventually a transaction without fees might reach a high enough priority to be included in the block for free.

Bitcoin transactions do not have an expiration time-out. A transaction that is valid now will be valid in perpetuity. However, if a transaction is only propagated across the network once, it will persist only as long as it is held in a mining node memory pool. When a mining node is restarted, its memory pool is wiped clear, because it is a transient non-persistent form of storage.

Although a valid transaction might have been propagated across the network, if it is not executed it may eventually not reside in the memory pool of any miner. Wallet software is expected to retransmit such transactions or reconstruct them with higher fees if they are not successfully executed within a reasonable amount of time.

The first transaction added to the block is a special transaction, called a generation transaction or coinbase transaction. Unlike regular transactions, the generation transaction does not consume spend UTXO as inputs. Instead, it has only one input, called the coinbase , which creates bitcoin from nothing.

The output of the generation transaction sends the value of The fees are calculated as:. The reward is calculated based on the block height, starting at 50 bitcoins per block and reduced by half every , blocks. Because this block is at height ,, the correct reward is 25 bitcoins.

The initial subsidy is calculated in satoshis by multiplying 50 with the COIN constant ,, satoshis. This sets the initial reward nSubsidy at 5 billion satoshis. Next, the function calculates the number of halvings that have occurred by dividing the current block height by the halving interval SubsidyHalvingInterval.

In the case of block ,, with a halving interval every , blocks, the result is 1 halving. The maximum number of halvings allowed is 64, so the code imposes a zero reward return only the fees if the 64 halvings is exceeded. Next, the function uses the binary-right-shift operator to divide the reward nSubsidy by two for each round of halving. In the case of block ,, this would binary-right-shift the reward of 5 billion satoshis once one halving and result in 2.

The binary-right-shift operator is used because it is more efficient for division by two than integer or floating-point division. Finally, the coinbase reward nSubsidy is added to the transaction fees nFees , and the sum is returned. In a generation transaction, the first two fields are set to values that do not represent a UTXO reference. Generation transactions do not have an unlocking script a. Instead, this field is replaced by coinbase data, which must be between 2 and bytes.

Except for the first few bytes, the rest of the coinbase data can be used by miners in any way they want; it is arbitrary data. Currently, miners use the coinbase data to include extra nonce values and strings identifying the mining pool, as we will see in the following sections. The first few bytes of the coinbase used to be arbitrary, but that is no longer the case.

The next three bytes, 0xb04 , are the block height encoded in little-endian format backward, least significant byte first. Reverse the order of the bytes and the result is 0xb44 , which is , in decimal. The next few hexadecimal digits are used to encode an extra nonce see The Extra Nonce Solution , or random value, used to find a suitable proof of work solution. Note that the libbitcoin library contains a static copy of the genesis block, so the example code can retrieve the genesis block directly from the library.

At the time that block , was mined, the version number describing the block structure is version 2, which is encoded in little-endian format in 4 bytes as 0x The block header hash for block , is:. The next step is to summarize all the transactions with a merkle tree, in order to add the merkle root to the block header. The generation transaction is listed as the first transaction in the block. Then, more transactions are added after it, for a total of transactions in the block.

The node then fills in the difficulty target, which defines the required proof-of-work difficulty to make this a valid block. The encoding has a 1-byte exponent, followed by a 3-byte mantissa coefficient. In block ,, for example, the difficulty bits value is 0xa30c. The first part 0x19 is a hexadecimal exponent, while the next part, 0x03a30c , is the coefficient.

The final field is the nonce, which is initialized to zero. With all the other fields filled, the block header is now complete and the process of mining can begin. The goal is now to find a value for the nonce that results in a block header hash that is less than the difficulty target.

The mining node will need to test billions or trillions of nonce values before a nonce is found that satisfies the requirement. Throughout this book we have studied cryptographic hash functions as used in various aspects of the bitcoin system.

In the simplest terms, mining is the process of hashing the block header repeatedly, changing one parameter, until the resulting hash matches a specific target. This feature of hash functions means that the only way to produce a hash result matching a specific target is to try again and again, randomly modifying the input until the desired hash result appears by chance. A hash algorithm takes an arbitrary-length data input and produces a fixed-length deterministic result, a digital fingerprint of the input.

For any specific input, the resulting hash will always be the same and can be easily calculated and verified by anyone implementing the same hash algorithm. The key characteristic of a cryptographic hash algorithm is that it is virtually impossible to find two different inputs that produce the same fingerprint. As a corollary, it is also virtually impossible to select an input in such a way as to produce a desired fingerprint, other than trying random inputs.

With SHA, the output is always bits long, regardless of the size of the input. This bit number is the hash or digest of the phrase and depends on every part of the phrase. Adding a single letter, punctuation mark, or any other character will produce a different hash. Now, if we change the phrase, we should expect to see completely different hashes. Running this will produce the hashes of several phrases, made different by adding a number at the end of the text.

Each phrase produces a completely different hash result. They seem completely random, but you can reproduce the exact results in this example on any computer with Python and see the same exact hashes. The number used as a variable in such a scenario is called a nonce.

The nonce is used to vary the output of a cryptographic function, in this case to vary the SHA fingerprint of the phrase. It took 13 attempts to find it. In terms of probabilities, if the output of the hash function is evenly distributed we would expect to find a result with a 0 as the hexadecimal prefix once every 16 hashes one out of 16 hexadecimal digits 0 through F.

In numerical terms, that means finding a hash value that is less than 0x We call this threshold the target and the goal is to find a hash that is numerically less than the target. If we decrease the target, the task of finding a hash that is less than the target becomes more and more difficult. To give a simple analogy, imagine a game where players throw a pair of dice repeatedly, trying to throw less than a specified target.

In the first round, the target is Unless you throw double-six, you win. In the next round the target is Players must throw 10 or less to win, again an easy task. Now, more than half the dice throws will add up to more than 5 and therefore be invalid. It takes exponentially more dice throws to win, the lower the target gets. The successful result is also proof of work, because it proves we did the work to find that nonce.

While it only takes one hash computation to verify, it took us 13 hash computations to find a nonce that worked. If we had a lower target higher difficulty it would take many more hash computations to find a suitable nonce, but only one hash computation for anyone to verify. Furthermore, by knowing the target, anyone can estimate the difficulty using statistics and therefore know how much work was needed to find such a nonce.

The miner constructs a candidate block filled with transactions. If the hash is not less than the target, the miner will modify the nonce usually just incrementing it by one and try again. At the current difficulty in the bitcoin network, miners have to try quadrillions of times before finding a nonce that results in a low enough block header hash.

Running this code, you can set the desired difficulty in bits, how many of the leading bits must be zero and see how long it takes for your computer to find a solution. As you can see, increasing the difficulty by 1 bit causes an exponential increase in the time it takes to find a solution.

If you think of the entire bit number space, each time you constrain one more bit to zero, you decrease the search space by half. Even at a speed of more than , hashes per second, it still requires 10 minutes on a consumer laptop to find this solution. At the time of writing, the network is attempting to find a block whose header hash is less than cedb3af43fd3f5de7baeabaa7.

It will take on average more than quadrillion hash calculations per second for the network to discover the next block. In this block, therefore, the exponent is 0x19 and the coefficient is 0x03a30c. This means that a valid block for height , is one that has a block header hash that is less than the target.

In binary that number would have more than the first 60 bits set to zero. As we saw, the target determines the difficulty and therefore affects how long it takes to find a solution to the proof-of-work algorithm. This leads to the obvious questions: Why is the difficulty adjustable, who adjusts it, and how? It has to remain constant not just over the short term, but over a period of many decades.

Over this time, it is expected that computer power will continue to increase at a rapid pace. Furthermore, the number of participants in mining and the computers they use will also constantly change. To keep the block generation time at 10 minutes, the difficulty of mining must be adjusted to account for these changes.

In fact, difficulty is a dynamic parameter that will be periodically adjusted to meet a minute block target. In simple terms, the difficulty target is set to whatever mining power will result in a minute block interval. How, then, is such an adjustment made in a completely decentralized network? Difficulty retargeting occurs automatically and on every full node independently.

Every 2, blocks, all nodes retarget the proof-of-work difficulty. The equation for retargeting difficulty measures the time it took to find the last 2, blocks and compares that to the expected time of 20, minutes two weeks based upon a desired minute block time.

The ratio between the actual timespan and desired timespan is calculated and a corresponding adjustment up or down is made to the difficulty. In simple terms: If the network is finding blocks faster than every 10 minutes, the difficulty increases. If block discovery is slower than expected, the difficulty decreases. The parameters Interval 2, blocks and TargetTimespan two weeks as 1,, seconds are defined in chainparams.

To avoid extreme volatility in the difficulty, the retargeting adjustment must be less than a factor of four 4 per cycle. If the required difficulty adjustment is greater than a factor of four, it will be adjusted by the maximum and not more.

Any further adjustment will be accomplished in the next retargeting period because the imbalance will persist through the next 2, blocks. Therefore, large discrepancies between hashing power and difficulty might take several 2, block cycles to balance out. The difficulty of finding a bitcoin block is approximately 10 minutes of processing for the entire network, based on the time it took to find the previous 2, blocks, adjusted every 2, blocks. Note that the target difficulty is independent of the number of transactions or the value of transactions.

This means that the amount of hashing power and therefore electricity expended to secure bitcoin is also entirely independent of the number of transactions. The increase in hashing power represents market forces as new miners enter the market to compete for the reward.

The target difficulty is closely related to the cost of electricity and the exchange rate of bitcoin vis-a-vis the currency used to pay for electricity. High-performance mining systems are about as efficient as possible with the current generation of silicon fabrication, converting electricity into hashing computation at the highest rate possible. The primary influence on the mining market is the price of one kilowatt-hour in bitcoin, because that determines the profitability of mining and therefore the incentives to enter or exit the mining market.

Jing has several hardware mining rigs with application-specific integrated circuits, where hundreds of thousands of integrated circuits run the SHA algorithm in parallel at incredible speeds. These specialized machines are connected to his mining node over USB. Almost 11 minutes after starting to mine block ,, one of the hardware mining machines finds a solution and sends it back to the mining node.

When inserted into the block header, the nonce 4,,, produces a block hash of:. They receive, validate, and then propagate the new block. As the block ripples out across the network, each node adds it to its own copy of the blockchain, extending it to a new height of , blocks. As mining nodes receive and validate the block, they abandon their efforts to find a block at the same height and immediately start computing the next block in the chain.

As the newly solved block moves across the network, each node performs a series of tests to validate it before propagating it to its peers. This ensures that only valid blocks are propagated on the network. The independent validation also ensures that miners who act honestly get their blocks incorporated in the blockchain, thus earning the reward. Those miners who act dishonestly have their blocks rejected and not only lose the reward, but also waste the effort expended to find a proof-of-work solution, thus incurring the cost of electricity without compensation.

When a node receives a new block, it will validate the block by checking it against a long list of criteria that must all be met; otherwise, the block is rejected. In previous sections we saw how the miners get to write a transaction that awards them the new bitcoins created within the block and claim the transaction fees.

Because every node validates blocks according to the same rules. An invalid coinbase transaction would make the entire block invalid, which would result in the block being rejected and, therefore, that transaction would never become part of the ledger.

The miners have to construct a perfect block, based on the shared rules that all nodes follow, and mine it with a correct solution to the proof of work. To do so, they expend a lot of electricity in mining, and if they cheat, all the electricity and effort is wasted. This is why independent validation is a key component of decentralized consensus. Once a node has validated a new block, it will then attempt to assemble a chain by connecting the block to the existing blockchain.

Nodes maintain three sets of blocks: those connected to the main blockchain, those that form branches off the main blockchain secondary chains , and finally, blocks that do not have a known parent in the known chains orphans. Invalid blocks are rejected as soon as any one of the validation criteria fails and are therefore not included in any chain.

Under most circumstances this is also the chain with the most blocks in it, unless there are two equal-length chains and one has more proof of work. These blocks are valid but not part of the main chain. They are kept for future reference, in case one of those chains is extended to exceed the main chain in difficulty. In the next section Blockchain Forks , we will see how secondary chains occur as a result of an almost simultaneous mining of blocks at the same height. When a new block is received, a node will try to slot it into the existing blockchain.

Then, the node will attempt to find that parent in the existing blockchain. For example, the new block , has a reference to the hash of its parent block , Most nodes that receive , will already have block , as the tip of their main chain and will therefore link the new block and extend that chain.

Sometimes, as we will see in Blockchain Forks , the new block extends a chain that is not the main chain. In that case, the node will attach the new block to the secondary chain it extends and then compare the difficulty of the secondary chain to the main chain. If the secondary chain has more cumulative difficulty than the main chain, the node will reconverge on the secondary chain, meaning it will select the secondary chain as its new main chain, making the old main chain a secondary chain.

If the node is a miner, it will now construct a block extending this new, longer, chain. Once the parent is received and linked into the existing chains, the orphan can be pulled out of the orphan pool and linked to the parent, making it part of a chain. Orphan blocks usually occur when two blocks that were mined within a short time of each other are received in reverse order child before parent.

By selecting the greatest-difficulty chain, all nodes eventually achieve network-wide consensus. Temporary discrepancies between chains are resolved eventually as more proof of work is added, extending one of the possible chains. When they mine a new block and extend the chain, the new block itself represents their vote. In the next section we will look at how discrepancies between competing chains forks are resolved by the independent selection of the longest difficulty chain.

Because the blockchain is a decentralized data structure, different copies of it are not always consistent. Blocks might arrive at different nodes at different times, causing the nodes to have different perspectives of the blockchain. To resolve this, each node always selects and attempts to extend the chain of blocks that represents the most proof of work, also known as the longest chain or greatest cumulative difficulty chain.

By summing the difficulty recorded in each block in a chain, a node can calculate the total amount of proof of work that has been expended to create that chain. As long as all nodes select the longest cumulative difficulty chain, the global bitcoin network eventually converges to a consistent state.

Forks occur as temporary inconsistencies between versions of the blockchain, which are resolved by eventual reconvergence as more blocks are added to one of the forks. The diagram is a simplified representation of bitcoin as a global network. Rather, it forms a mesh network of interconnected nodes, which might be located very far from each other geographically.

The representation of a geographic topology is a simplification used for the purposes of illustrating a fork. For illustration purposes, different blocks are shown as different colors, spreading across the network and coloring the connections they traverse. This occurs under normal conditions whenever two miners solve the proof-of-work algorithm within a short period of time from each other. Each node that receives a valid block will incorporate it into its blockchain, extending the blockchain by one block.

If that node later sees another candidate block extending the same parent, it connects the second candidate on a secondary chain. Both of these blocks are children of the blue block, meant to extend the chain by building on top of the blue block. To help us track it, one is visualized as a red block originating from Canada, and the other is marked as a green block originating from Australia.

Both blocks are valid, both blocks contain a valid solution to the proof of work, and both blocks extend the same parent. Both blocks likely contain most of the same transactions, with only perhaps a few differences in the order of transactions.

Forks are almost always resolved within one block. The chain blue-green-pink is now longer more cumulative difficulty than the chain blue-red. This is a chain reconvergence, because those nodes are forced to revise their view of the blockchain to incorporate the new evidence of a longer chain. However, the chance of that happening is very low. Whereas a one-block fork might occur every week, a two-block fork is exceedingly rare.

A faster block time would make transactions clear faster but lead to more frequent blockchain forks, whereas a slower block time would decrease the number of forks but make settlement slower. Bitcoin mining is an extremely competitive industry. Some years the growth has reflected a complete change of technology, such as in and when many miners switched from using CPU mining to GPU mining and field programmable gate array FPGA mining.

In the introduction of ASIC mining lead to another giant leap in mining power, by placing the SHA function directly on silicon chips specialized for the purpose of mining. The first such chips could deliver more mining power in a single box than the entire bitcoin network in The following list shows the total hashing power of the bitcoin network, over the first five years of operation:.

As you can see, the competition between miners and the growth of bitcoin has resulted in an exponential increase in the hashing power total hashes per second across the network. As the amount of hashing power applied to mining bitcoin has exploded, the difficulty has risen to match it. In the last two years, the ASIC mining chips have become increasingly denser, approaching the cutting edge of silicon fabrication with a feature size resolution of 22 nanometers nm.

Currently, ASIC manufacturers are aiming to overtake general-purpose CPU chip manufacturers, designing chips with a feature size of 16nm, because the profitability of mining is driving this industry even faster than general computing. Still, the mining power of the network continues to advance at an exponential pace as the race for higher density chips is matched with a race for higher density data centers where thousands of these chips can be deployed. Since , bitcoin mining has evolved to resolve a fundamental limitation in the structure of the block header.

In the early days of bitcoin, a miner could find a block by iterating through the nonce until the resulting hash was below the target. As difficulty increased, miners often cycled through all 4 billion values of the nonce without finding a block. However, this was easily resolved by updating the block timestamp to account for the elapsed time. Because the timestamp is part of the header, the change would allow miners to iterate through the values of the nonce again with different results.

The timestamp could be stretched a bit, but moving it too far into the future would cause the block to become invalid. The solution was to use the coinbase transaction as a source of extra nonce values. Because the coinbase script can store between 2 and bytes of data, miners started using that space as extra nonce space, allowing them to explore a much larger range of block header values to find valid blocks. The coinbase transaction is included in the merkle tree, which means that any change in the coinbase script causes the merkle root to change.

If, in the future, miners could run through all these possibilities, they could then modify the timestamp. There is also more space in the coinbase script for future expansion of the extra nonce space. The likelihood of them finding a block to offset their electricity and hardware costs is so low that it represents a gamble, like playing the lottery. Even the fastest consumer ASIC mining system cannot keep up with commercial systems that stack tens of thousands of these chips in giant warehouses near hydro-electric power stations.

Miners now collaborate to form mining pools, pooling their hashing power and sharing the reward among thousands of participants. By participating in a pool, miners get a smaller share of the overall reward, but typically get rewarded every day, reducing uncertainty. At current bitcoin difficulty, the miner will be able to solo mine a block approximately once every days, or every 5 months.

He might find two blocks in five months and make a very large profit. Or he might not find a block for 10 months and suffer a financial loss. Even worse, the difficulty of the bitcoin proof-of-work algorithm is likely to go up significantly over that period, at the current rate of growth of hashing power, meaning the miner has, at most, six months to break even before the hardware is effectively obsolete and must be replaced by more powerful mining hardware.

The regular payouts from a mining pool will help him amortize the cost of hardware and electricity over time without taking an enormous risk. The hardware will still be obsolete in six to nine months and the risk is still high, but the revenue is at least regular and reliable over that period.

No matter what Bitcoin software you use, you should never buy more bitcoins than you can afford to lose. Bitcoin is still an experimental system and bitcoins remain a risky investment. Bitcoin Core puts you in charge of your wallet, which means your bitcoins are at risk unless you complete certain tasks:.

Make sure your wallet is secure. Setup an offline wallet cold storage for significant amounts of bitcoins. Allow your heirs to receive your bitcoins if you die or become incapacitated. Learn more: Bitcoin Core configuration options. Legal: Bitcoin use is prohibited or restricted in some areas. Worse, some providers may terminate your connection without warning because of overuse. We advise that you check whether your Internet connection is subjected to such limitations and monitor your bandwidth use so that you can stop Bitcoin Core before you reach your upload limit.

Anti-virus: Several people have placed parts of known computer viruses in the Bitcoin block chain. This problem mostly affects computers running Windows. Attack target: Bitcoin Core powers the Bitcoin peer-to-peer network, so people who want to disrupt the network may attack Bitcoin Core users in ways that will affect other things you do with your computer, such as an attack that limits your available download bandwidth.

By default, you need to backup Bitcoin Core after every transactions. This includes both transactions you send as well as payments you request whether or not you actually received the payment. For example, you need to backup after sending 33 payments and requesting 67 payments even though you only received 60 payments. Bitcoin Core can be configured to allow you to go more transactions between backups. See the -keypool setting.

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By contrast, the verification only requires K and less than one 10th of a second. Plus, I don't know of many exchanges that deal with it, nor how much it's worth - so can't say for sure if mining such coin would be the most profitable for you or simply the most efficient. I'm sure your machine would have a slight advantage at mining other CPU-only coins, have you tried Protoshares or Quarkcoin?

Try to search memory-intensive in whitepapers. Sign up to join this community. The best answers are voted up and rise to the top. Coins with memory-intensive mining Ask Question. Asked 6 years, 11 months ago. Active 1 year, 5 months ago. Viewed 18k times. Improve this question. Kozuch Kozuch 1, 3 3 gold badges 11 11 silver badges 26 26 bronze badges. Add a comment.

Active Oldest Votes. Improve this answer. David Perry David Perry In what sense is using main memory a "loss of efficiency"? The goal of a memory-bound proof-of-work is not "to maximize hashrate". Hash-rate is just some arbitrary measure that's not comparable across different proofs-of-work.

Scrypt simply has to do a lot more work per hash. The same goes for a memory-bound pow that needs to do a lot of work accessing main memory. If anything,aA PoW dominated by main memory latency is more power efficient.

By contrast, the verification only requires K and less than one 10th of a second Be warned, though, it also requires a fast CPU from same page: "it has a large AES component — chips with AES-NI instruction sets will fare much better". Joe Pineda Joe Pineda 2, 2 2 gold badges 15 15 silver badges 28 28 bronze badges. John Tromp John Tromp 2 2 bronze badges. I don't think memory access time is what's meant by "memory-intensive mining". Usually that means the process uses a lot of memory space, not bus bandwidth.

Cuckoo Cycle uses both; lots of memory space and bandwidth. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. The first part 0x19 is a hexadecimal exponent, while the next part, 0x03a30c , is the coefficient.

The final field is the nonce, which is initialized to zero. With all the other fields filled, the block header is now complete and the process of mining can begin. The goal is now to find a value for the nonce that results in a block header hash that is less than the difficulty target. The mining node will need to test billions or trillions of nonce values before a nonce is found that satisfies the requirement.

Throughout this book we have studied cryptographic hash functions as used in various aspects of the bitcoin system. In the simplest terms, mining is the process of hashing the block header repeatedly, changing one parameter, until the resulting hash matches a specific target. This feature of hash functions means that the only way to produce a hash result matching a specific target is to try again and again, randomly modifying the input until the desired hash result appears by chance.

A hash algorithm takes an arbitrary-length data input and produces a fixed-length deterministic result, a digital fingerprint of the input. For any specific input, the resulting hash will always be the same and can be easily calculated and verified by anyone implementing the same hash algorithm. The key characteristic of a cryptographic hash algorithm is that it is virtually impossible to find two different inputs that produce the same fingerprint.

As a corollary, it is also virtually impossible to select an input in such a way as to produce a desired fingerprint, other than trying random inputs. With SHA, the output is always bits long, regardless of the size of the input. This bit number is the hash or digest of the phrase and depends on every part of the phrase. Adding a single letter, punctuation mark, or any other character will produce a different hash. Now, if we change the phrase, we should expect to see completely different hashes.

Running this will produce the hashes of several phrases, made different by adding a number at the end of the text. Each phrase produces a completely different hash result. They seem completely random, but you can reproduce the exact results in this example on any computer with Python and see the same exact hashes. The number used as a variable in such a scenario is called a nonce.

The nonce is used to vary the output of a cryptographic function, in this case to vary the SHA fingerprint of the phrase. It took 13 attempts to find it. In terms of probabilities, if the output of the hash function is evenly distributed we would expect to find a result with a 0 as the hexadecimal prefix once every 16 hashes one out of 16 hexadecimal digits 0 through F. In numerical terms, that means finding a hash value that is less than 0x We call this threshold the target and the goal is to find a hash that is numerically less than the target.

If we decrease the target, the task of finding a hash that is less than the target becomes more and more difficult. To give a simple analogy, imagine a game where players throw a pair of dice repeatedly, trying to throw less than a specified target. In the first round, the target is Unless you throw double-six, you win. In the next round the target is Players must throw 10 or less to win, again an easy task.

Now, more than half the dice throws will add up to more than 5 and therefore be invalid. It takes exponentially more dice throws to win, the lower the target gets. The successful result is also proof of work, because it proves we did the work to find that nonce.

While it only takes one hash computation to verify, it took us 13 hash computations to find a nonce that worked. If we had a lower target higher difficulty it would take many more hash computations to find a suitable nonce, but only one hash computation for anyone to verify.

Furthermore, by knowing the target, anyone can estimate the difficulty using statistics and therefore know how much work was needed to find such a nonce. The miner constructs a candidate block filled with transactions. If the hash is not less than the target, the miner will modify the nonce usually just incrementing it by one and try again. At the current difficulty in the bitcoin network, miners have to try quadrillions of times before finding a nonce that results in a low enough block header hash.

Running this code, you can set the desired difficulty in bits, how many of the leading bits must be zero and see how long it takes for your computer to find a solution. As you can see, increasing the difficulty by 1 bit causes an exponential increase in the time it takes to find a solution. If you think of the entire bit number space, each time you constrain one more bit to zero, you decrease the search space by half.

Even at a speed of more than , hashes per second, it still requires 10 minutes on a consumer laptop to find this solution. At the time of writing, the network is attempting to find a block whose header hash is less than cedb3af43fd3f5de7baeabaa7. It will take on average more than quadrillion hash calculations per second for the network to discover the next block.

In this block, therefore, the exponent is 0x19 and the coefficient is 0x03a30c. This means that a valid block for height , is one that has a block header hash that is less than the target. In binary that number would have more than the first 60 bits set to zero.

As we saw, the target determines the difficulty and therefore affects how long it takes to find a solution to the proof-of-work algorithm. This leads to the obvious questions: Why is the difficulty adjustable, who adjusts it, and how? It has to remain constant not just over the short term, but over a period of many decades.

Over this time, it is expected that computer power will continue to increase at a rapid pace. Furthermore, the number of participants in mining and the computers they use will also constantly change. To keep the block generation time at 10 minutes, the difficulty of mining must be adjusted to account for these changes. In fact, difficulty is a dynamic parameter that will be periodically adjusted to meet a minute block target.

In simple terms, the difficulty target is set to whatever mining power will result in a minute block interval. How, then, is such an adjustment made in a completely decentralized network? Difficulty retargeting occurs automatically and on every full node independently.

Every 2, blocks, all nodes retarget the proof-of-work difficulty. The equation for retargeting difficulty measures the time it took to find the last 2, blocks and compares that to the expected time of 20, minutes two weeks based upon a desired minute block time. The ratio between the actual timespan and desired timespan is calculated and a corresponding adjustment up or down is made to the difficulty. In simple terms: If the network is finding blocks faster than every 10 minutes, the difficulty increases.

If block discovery is slower than expected, the difficulty decreases. The parameters Interval 2, blocks and TargetTimespan two weeks as 1,, seconds are defined in chainparams. To avoid extreme volatility in the difficulty, the retargeting adjustment must be less than a factor of four 4 per cycle. If the required difficulty adjustment is greater than a factor of four, it will be adjusted by the maximum and not more.

Any further adjustment will be accomplished in the next retargeting period because the imbalance will persist through the next 2, blocks. Therefore, large discrepancies between hashing power and difficulty might take several 2, block cycles to balance out. The difficulty of finding a bitcoin block is approximately 10 minutes of processing for the entire network, based on the time it took to find the previous 2, blocks, adjusted every 2, blocks.

Note that the target difficulty is independent of the number of transactions or the value of transactions. This means that the amount of hashing power and therefore electricity expended to secure bitcoin is also entirely independent of the number of transactions. The increase in hashing power represents market forces as new miners enter the market to compete for the reward.

The target difficulty is closely related to the cost of electricity and the exchange rate of bitcoin vis-a-vis the currency used to pay for electricity. High-performance mining systems are about as efficient as possible with the current generation of silicon fabrication, converting electricity into hashing computation at the highest rate possible.

The primary influence on the mining market is the price of one kilowatt-hour in bitcoin, because that determines the profitability of mining and therefore the incentives to enter or exit the mining market. Jing has several hardware mining rigs with application-specific integrated circuits, where hundreds of thousands of integrated circuits run the SHA algorithm in parallel at incredible speeds.

These specialized machines are connected to his mining node over USB. Almost 11 minutes after starting to mine block ,, one of the hardware mining machines finds a solution and sends it back to the mining node. When inserted into the block header, the nonce 4,,, produces a block hash of:. They receive, validate, and then propagate the new block. As the block ripples out across the network, each node adds it to its own copy of the blockchain, extending it to a new height of , blocks.

As mining nodes receive and validate the block, they abandon their efforts to find a block at the same height and immediately start computing the next block in the chain. As the newly solved block moves across the network, each node performs a series of tests to validate it before propagating it to its peers. This ensures that only valid blocks are propagated on the network. The independent validation also ensures that miners who act honestly get their blocks incorporated in the blockchain, thus earning the reward.

Those miners who act dishonestly have their blocks rejected and not only lose the reward, but also waste the effort expended to find a proof-of-work solution, thus incurring the cost of electricity without compensation. When a node receives a new block, it will validate the block by checking it against a long list of criteria that must all be met; otherwise, the block is rejected. In previous sections we saw how the miners get to write a transaction that awards them the new bitcoins created within the block and claim the transaction fees.

Because every node validates blocks according to the same rules. An invalid coinbase transaction would make the entire block invalid, which would result in the block being rejected and, therefore, that transaction would never become part of the ledger. The miners have to construct a perfect block, based on the shared rules that all nodes follow, and mine it with a correct solution to the proof of work.

To do so, they expend a lot of electricity in mining, and if they cheat, all the electricity and effort is wasted. This is why independent validation is a key component of decentralized consensus. Once a node has validated a new block, it will then attempt to assemble a chain by connecting the block to the existing blockchain. Nodes maintain three sets of blocks: those connected to the main blockchain, those that form branches off the main blockchain secondary chains , and finally, blocks that do not have a known parent in the known chains orphans.

Invalid blocks are rejected as soon as any one of the validation criteria fails and are therefore not included in any chain. Under most circumstances this is also the chain with the most blocks in it, unless there are two equal-length chains and one has more proof of work. These blocks are valid but not part of the main chain. They are kept for future reference, in case one of those chains is extended to exceed the main chain in difficulty. In the next section Blockchain Forks , we will see how secondary chains occur as a result of an almost simultaneous mining of blocks at the same height.

When a new block is received, a node will try to slot it into the existing blockchain. Then, the node will attempt to find that parent in the existing blockchain. For example, the new block , has a reference to the hash of its parent block , Most nodes that receive , will already have block , as the tip of their main chain and will therefore link the new block and extend that chain.

Sometimes, as we will see in Blockchain Forks , the new block extends a chain that is not the main chain. In that case, the node will attach the new block to the secondary chain it extends and then compare the difficulty of the secondary chain to the main chain. If the secondary chain has more cumulative difficulty than the main chain, the node will reconverge on the secondary chain, meaning it will select the secondary chain as its new main chain, making the old main chain a secondary chain.

If the node is a miner, it will now construct a block extending this new, longer, chain. Once the parent is received and linked into the existing chains, the orphan can be pulled out of the orphan pool and linked to the parent, making it part of a chain. Orphan blocks usually occur when two blocks that were mined within a short time of each other are received in reverse order child before parent.

By selecting the greatest-difficulty chain, all nodes eventually achieve network-wide consensus. Temporary discrepancies between chains are resolved eventually as more proof of work is added, extending one of the possible chains. When they mine a new block and extend the chain, the new block itself represents their vote. In the next section we will look at how discrepancies between competing chains forks are resolved by the independent selection of the longest difficulty chain.

Because the blockchain is a decentralized data structure, different copies of it are not always consistent. Blocks might arrive at different nodes at different times, causing the nodes to have different perspectives of the blockchain. To resolve this, each node always selects and attempts to extend the chain of blocks that represents the most proof of work, also known as the longest chain or greatest cumulative difficulty chain.

By summing the difficulty recorded in each block in a chain, a node can calculate the total amount of proof of work that has been expended to create that chain. As long as all nodes select the longest cumulative difficulty chain, the global bitcoin network eventually converges to a consistent state. Forks occur as temporary inconsistencies between versions of the blockchain, which are resolved by eventual reconvergence as more blocks are added to one of the forks.

The diagram is a simplified representation of bitcoin as a global network. Rather, it forms a mesh network of interconnected nodes, which might be located very far from each other geographically. The representation of a geographic topology is a simplification used for the purposes of illustrating a fork.

For illustration purposes, different blocks are shown as different colors, spreading across the network and coloring the connections they traverse. This occurs under normal conditions whenever two miners solve the proof-of-work algorithm within a short period of time from each other.

Each node that receives a valid block will incorporate it into its blockchain, extending the blockchain by one block. If that node later sees another candidate block extending the same parent, it connects the second candidate on a secondary chain. Both of these blocks are children of the blue block, meant to extend the chain by building on top of the blue block. To help us track it, one is visualized as a red block originating from Canada, and the other is marked as a green block originating from Australia.

Both blocks are valid, both blocks contain a valid solution to the proof of work, and both blocks extend the same parent. Both blocks likely contain most of the same transactions, with only perhaps a few differences in the order of transactions. Forks are almost always resolved within one block. The chain blue-green-pink is now longer more cumulative difficulty than the chain blue-red.

This is a chain reconvergence, because those nodes are forced to revise their view of the blockchain to incorporate the new evidence of a longer chain. However, the chance of that happening is very low. Whereas a one-block fork might occur every week, a two-block fork is exceedingly rare. A faster block time would make transactions clear faster but lead to more frequent blockchain forks, whereas a slower block time would decrease the number of forks but make settlement slower.

Bitcoin mining is an extremely competitive industry. Some years the growth has reflected a complete change of technology, such as in and when many miners switched from using CPU mining to GPU mining and field programmable gate array FPGA mining.

In the introduction of ASIC mining lead to another giant leap in mining power, by placing the SHA function directly on silicon chips specialized for the purpose of mining. The first such chips could deliver more mining power in a single box than the entire bitcoin network in The following list shows the total hashing power of the bitcoin network, over the first five years of operation:.

As you can see, the competition between miners and the growth of bitcoin has resulted in an exponential increase in the hashing power total hashes per second across the network. As the amount of hashing power applied to mining bitcoin has exploded, the difficulty has risen to match it. In the last two years, the ASIC mining chips have become increasingly denser, approaching the cutting edge of silicon fabrication with a feature size resolution of 22 nanometers nm.

Currently, ASIC manufacturers are aiming to overtake general-purpose CPU chip manufacturers, designing chips with a feature size of 16nm, because the profitability of mining is driving this industry even faster than general computing. Still, the mining power of the network continues to advance at an exponential pace as the race for higher density chips is matched with a race for higher density data centers where thousands of these chips can be deployed.

Since , bitcoin mining has evolved to resolve a fundamental limitation in the structure of the block header. In the early days of bitcoin, a miner could find a block by iterating through the nonce until the resulting hash was below the target. As difficulty increased, miners often cycled through all 4 billion values of the nonce without finding a block.

However, this was easily resolved by updating the block timestamp to account for the elapsed time. Because the timestamp is part of the header, the change would allow miners to iterate through the values of the nonce again with different results. The timestamp could be stretched a bit, but moving it too far into the future would cause the block to become invalid. The solution was to use the coinbase transaction as a source of extra nonce values.

Because the coinbase script can store between 2 and bytes of data, miners started using that space as extra nonce space, allowing them to explore a much larger range of block header values to find valid blocks. The coinbase transaction is included in the merkle tree, which means that any change in the coinbase script causes the merkle root to change. If, in the future, miners could run through all these possibilities, they could then modify the timestamp.

There is also more space in the coinbase script for future expansion of the extra nonce space. The likelihood of them finding a block to offset their electricity and hardware costs is so low that it represents a gamble, like playing the lottery. Even the fastest consumer ASIC mining system cannot keep up with commercial systems that stack tens of thousands of these chips in giant warehouses near hydro-electric power stations. Miners now collaborate to form mining pools, pooling their hashing power and sharing the reward among thousands of participants.

By participating in a pool, miners get a smaller share of the overall reward, but typically get rewarded every day, reducing uncertainty. At current bitcoin difficulty, the miner will be able to solo mine a block approximately once every days, or every 5 months.

He might find two blocks in five months and make a very large profit. Or he might not find a block for 10 months and suffer a financial loss. Even worse, the difficulty of the bitcoin proof-of-work algorithm is likely to go up significantly over that period, at the current rate of growth of hashing power, meaning the miner has, at most, six months to break even before the hardware is effectively obsolete and must be replaced by more powerful mining hardware.

The regular payouts from a mining pool will help him amortize the cost of hardware and electricity over time without taking an enormous risk. The hardware will still be obsolete in six to nine months and the risk is still high, but the revenue is at least regular and reliable over that period. Mining pools coordinate many hundreds or thousands of miners, over specialized pool-mining protocols.

The individual miners configure their mining equipment to connect to a pool server, after creating an account with the pool. Their mining hardware remains connected to the pool server while mining, synchronizing their efforts with the other miners. Thus, the pool miners share the effort to mine a block and then share in the rewards. Successful blocks pay the reward to a pool bitcoin address, rather than individual miners.

Typically, the pool server charges a percentage fee of the rewards for providing the pool-mining service. When someone in the pool successfully mines a block, the reward is earned by the pool and then shared with all miners in proportion to the number of shares they contributed to the effort. Pools are open to any miner, big or small, professional or amateur. A pool will therefore have some participants with a single small mining machine, and others with a garage full of high-end mining hardware.

Some will be mining with a few tens of a kilowatt of electricity, others will be running a data center consuming a megawatt of power. How does a mining pool measure the individual contributions, so as to fairly distribute the rewards, without the possibility of cheating? By setting a lower difficulty for earning shares, the pool measures the amount of work done by each miner.

Each time a pool miner finds a block header hash that is less than the pool difficulty, she proves she has done the hashing work to find that result. Thousands of miners trying to find low-value hashes will eventually find one low enough to satisfy the bitcoin network target. If the dice players are throwing dice with a goal of throwing less than four the overall network difficulty , a pool would set an easier target, counting how many times the pool players managed to throw less than eight.

Every now and then, one of the pool players will throw a combined dice throw of less than four and the pool wins. Then, the earnings can be distributed to the pool players based on the shares they earned. Similarly, a mining pool will set a pool difficulty that will ensure that an individual pool miner can find block header hashes that are less than the pool difficulty quite often, earning shares. Every now and then, one of these attempts will produce a block header hash that is less than the bitcoin network target, making it a valid block and the whole pool wins.

The owner of the pool server is called the pool operator , and he charges pool miners a percentage fee of the earnings. The pool server runs specialized software and a pool-mining protocol that coordinates the activities of the pool miners. The pool server is also connected to one or more full bitcoin nodes and has direct access to a full copy of the blockchain database. This allows the pool server to validate blocks and transactions on behalf of the pool miners, relieving them of the burden of running a full node.

For pool miners, this is an important consideration, because a full node requires a dedicated computer with at least 15 to 20 GB of persistent storage disk and at least 2 GB of memory RAM. Furthermore, the bitcoin software running on the full node needs to be monitored, maintained, and upgraded frequently. For many miners, the ability to mine without running a full node is another big benefit of joining a managed pool.

The pool server constructs a candidate block by aggregating transactions, adding a coinbase transaction with extra nonce space , calculating the merkle root, and linking to the previous block hash. The header of the candidate block is then sent to each of the pool miners as a template. Each pool miner then mines using the block template, at a lower difficulty than the bitcoin network difficulty, and sends any successful results back to the pool server to earn shares. Managed pools create the possibility of cheating by the pool operator, who might direct the pool effort to double-spend transactions or invalidate blocks see Consensus Attacks.

Furthermore, centralized pool servers represent a single-point-of-failure. If the pool server is down or is slowed by a denial-of-service attack, the pool miners cannot mine. In , to resolve these issues of centralization, a new pool mining method was proposed and implemented: P2Pool is a peer-to-peer mining pool, without a central operator. P2Pool works by decentralizing the functions of the pool server, implementing a parallel blockchain-like system called a share chain. A share chain is a blockchain running at a lower difficulty than the bitcoin blockchain.

The share chain allows pool miners to collaborate in a decentralized pool, by mining shares on the share chain at a rate of one share block every 30 seconds. Each of the blocks on the share chain records a proportionate share reward for the pool miners who contribute work, carrying the shares forward from the previous share block. When one of the share blocks also achieves the difficulty target of the bitcoin network, it is propagated and included on the bitcoin blockchain, rewarding all the pool miners who contributed to all the shares that preceded the winning share block.

P2Pool mining is more complex than pool mining because it requires that the pool miners run a dedicated computer with enough disk space, memory, and Internet bandwidth to support a full bitcoin node and the P2Pool node software. P2Pool miners connect their mining hardware to their local P2Pool node, which simulates the functions of a pool server by sending block templates to the mining hardware.

On P2Pool, individual pool miners construct their own candidate blocks, aggregating transactions much like solo miners, but then mine collaboratively on the share chain. P2Pool is a hybrid approach that has the advantage of much more granular payouts than solo mining, but without giving too much control to a pool operator like managed pools. Further development of the P2Pool protocol continues with the expectation of removing the need for running a full node and therefore making decentralized mining even easier to use.

As we saw, the consensus mechanism depends on having a majority of the miners acting honestly out of self-interest. However, if a miner or group of miners can achieve a significant share of the mining power, they can attack the consensus mechanism so as to disrupt the security and availability of the bitcoin network. It is important to note that consensus attacks can only affect future consensus, or at best the most recent past tens of blocks. While in theory, a fork can be achieved at any depth, in practice, the computing power needed to force a very deep fork is immense, making old blocks practically immutable.

A consensus attack cannot steal bitcoins, spend bitcoins without signatures, redirect bitcoins, or otherwise change past transactions or ownership records. Consensus attacks can only affect the most recent blocks and cause denial-of-service disruptions on the creation of future blocks. With sufficient power, an attacker can invalidate six or more blocks in a row, causing transactions that were considered immutable six confirmations to be invalidated.

In the first chapter, we looked at a transaction between Alice and Bob for a cup of coffee. Bob, the cafe owner, is willing to accept payment for cups of coffee without waiting for confirmation mining in a block , because the risk of a double-spend on a cup of coffee is low in comparison to the convenience of rapid customer service. In contrast, selling a more expensive item for bitcoin runs the risk of a double-spend attack, where the buyer broadcasts a competing transaction that spends the same inputs UTXO and cancels the payment to the merchant.

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Asked 6 years, 11 months ago. Active 1 year, 5 months ago. Viewed 18k times. Improve this question. Kozuch Kozuch 1, 3 3 gold badges 11 11 silver badges 26 26 bronze badges. Add a comment. Active Oldest Votes. Improve this answer. David Perry David Perry In what sense is using main memory a "loss of efficiency"? The goal of a memory-bound proof-of-work is not "to maximize hashrate". Hash-rate is just some arbitrary measure that's not comparable across different proofs-of-work.

Scrypt simply has to do a lot more work per hash. The same goes for a memory-bound pow that needs to do a lot of work accessing main memory. If anything,aA PoW dominated by main memory latency is more power efficient. By contrast, the verification only requires K and less than one 10th of a second Be warned, though, it also requires a fast CPU from same page: "it has a large AES component — chips with AES-NI instruction sets will fare much better". Joe Pineda Joe Pineda 2, 2 2 gold badges 15 15 silver badges 28 28 bronze badges.

John Tromp John Tromp 2 2 bronze badges. I don't think memory access time is what's meant by "memory-intensive mining". Usually that means the process uses a lot of memory space, not bus bandwidth. Cuckoo Cycle uses both; lots of memory space and bandwidth.

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Visual design changes to the review queues. Memory Coin is a new cryptocurrency that aims to empower the economically and financially marginalized. It allows individuals to participate in the internet economy even when they live in countries where credit card companies and PayPal refuse to operate. Individuals can store and transfer wealth with just a memorized pass phrase.

Below you will learn how to mine memory coin. For memorycoin each thread also takes 1GB of Memory. So if you use 10 Thread you need 10GB of memory in the system. I recommend disable it for 15min. If you Download the MemoryCoin wallet it will also show up as a Bitcoin Mining Virus, It is not a virus since you know you want to run the program.

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