中本聪致迈克·赫恩：比特币的可扩展性（2009 年 4 月 12 日）
首次公开证据
打开首次公开证据嗨，Mike：
我很乐意回答你的任何问题。如果有时间，我应该写一份 FAQ 来补充论文。
只有一条全局链。
现有的 Visa 信用卡网络每天在全球处理约 1500 万笔互联网购买。使用现有硬件，比特币已经可以以一小部分成本扩展到远超这一规模。它实际上不会碰到规模上限。如果你感兴趣，我可以详细说明它将如何应对极端规模。
根据摩尔定律，我们可以预期硬件速度在 5 年内提高 10 倍，在 10 年内提高 100 倍。即使比特币以疯狂的采用速度增长，我认为计算机速度也会领先于交易数量。
我预计近期内不会需要费用，但如果运行节点变得过于繁重，可以运行一个只处理包含交易费的交易的节点。节点所有者会决定他们接受的最低费用。现在这样的节点什么也得不到，因为没有人包含费用；但如果足够多的节点这样做，用户包含费用时就会更快被接受，不包含时就会更慢。市场最终确定的费用应该很低。如果节点要求更高的费用，它就会放弃所有费用较低的交易。它可以处理更多交易，并且通过尽可能多地处理付费交易，可能赚到更多钱。不过，这一转变不是由某个掌管系统的人控制的，而只是个人自行对市场力量作出反应。
最终，大多数节点可能由拥有多张 GPU 卡的专业人士运行。现在，任何拥有 PC 的人都可以参与，而不用担心自己的显卡，这很不错，希望这种情况能维持一段时间。如今发货的计算机中有相当不错的 GPU 的越来越多，所以以后我们也许会转向 GPU。
比特币的一个关键特点是，网络安全性会随着网络规模以及需要保护的价值数量增长而增长。缺点是它在规模很小时的初期容易受到攻击，不过能够被窃取的价值应该始终小于窃取它所需的努力。如果有人有其他动机想证明某个观点，那他们只是在证明我已经承认的观点。
我对币的数量和分配计划的选择是经过思考的猜测。这是一个困难的选择，因为网络一旦运行起来就会锁定，我们只能接受它。我想选一个能使价格接近现有货币的方案，但不知道未来，这非常困难。最后我选了一个中间值。如果比特币仍然只是一个小众领域，它每单位的价值会低于现有货币。如果你设想它被用于世界贸易的一部分，那么全世界只有 2100 万个币，所以每单位的价值会高得多。价值是带有 8 位小数的 64 位整数，因此 1 个币在内部表示为 100000000。如果典型价格变小，粒度也完全足够。例如，如果 0.001 的价值是 1 欧元，那么可能更容易改变小数点的显示位置：如果你有 1 个比特币，现在它会显示为 1000，而 0.001 会显示为 1。
Ripple 很有意思，因为除了把信任集中到中央服务器之外，它是唯一一个以其他方式处理信任的系统。
Satoshi
英文原文
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Hi Mike,
I'm glad to answer any questions you have. If I get time, I ought to write a FAQ to supplement the paper.
There is only one global chain.
The existing Visa credit card network processes about 15 million Internet purchases per day worldwide. Bitcoin can already scale much larger than that with existing hardware for a fraction of the cost. It never really hits a scale ceiling. If you're interested, I can go over the ways it would cope with extreme size.
By Moore's Law, we can expect hardware speed to be 10 times faster in 5 years and 100 times faster in 10. Even if Bitcoin grows at crazy adoption rates, I think computer speeds will stay ahead of the number of transactions.
I don't anticipate that fees will be needed anytime soon, but if it becomes too burdensome to run a node, it is possible to run a node that only processes transactions that include a transaction fee. The owner of the node would decide the minimum fee they'll accept. Right now, such a node would get nothing, because nobody includes a fee, but if enough nodes did that, then users would get faster acceptance if they include a fee, or slower if they don't. The fee the market would settle on should be minimal. If a node requires a higher fee, that node would be passing up all transactions with lower fees. It could do more volume and probably make more money by processing as many paying transactions as it can. The transition is not controlled by some human in charge of the system though, just individuals reacting on their own to market forces.
Eventually, most nodes may be run by specialists with multiple GPU cards. For now, it's nice that anyone with a PC can play without worrying about what video card they have, and hopefully it'll stay that way for a while. More computers are shipping with fairly decent GPUs these days, so maybe later we'll transition to that.
A key aspect of Bitcoin is that the security of the network grows as the size of the network and the amount of value that needs to be protected grows. The down side is that it's vulnerable at the beginning when it's small, although the value that could be stolen should always be smaller than the amount of effort required to steal it. If someone has other motives to prove a point, they'll just be proving a point I already concede.
My choice for the number of coins and distribution schedule was an educated guess. It was a difficult choice, because once the network is going it's locked in and we're stuck with it. I wanted to pick something that would make prices similar to existing currencies, but without knowing the future, that's very hard. I ended up picking something in the middle. If Bitcoin remains a small niche, it'll be worth less per unit than existing currencies. If you imagine it being used for some fraction of world commerce, then there's only going to be 21 million coins for the whole world, so it would be worth much more per unit. Values are 64-bit integers with 8 decimal places, so 1 coin is represented internally as 100000000. There's plenty of granularity if typical prices become small. For example, if 0.001 is worth 1 Euro, then it might be easier to change where the decimal point is displayed, so if you had 1 Bitcoin it's now displayed as 1000, and 0.001 is displayed as 1.
Ripple is interesting in that it's the only other system that does something with trust besides concentrate it into a central server.
Satoshi