Scalability

The current system where every user is a network node is not the intended configuration for large scale. That would be like every Usenet user runs their own NNTP server. The design supports letting users just be users. The more burden it becomes to run a node, the fewer nodes there will be. Those few nodes will be big server farms. The rest will be client nodes that only do transactions and don’t generate.

A block header with no transactions would be about 80 bytes. If we suppose blocks are generated every 10 minutes, 80 bytes * 6 * 24 * 365 = 4.2MB per year. With computer systems typically selling with 2GB of RAM as of 2008, and Moore’s law predicting current growth of 1.2GB per year, storage should not be a problem even if the block headers must be kept in memory.

The design outlines a lightweight client that does not need the full block chain.  In the design PDF it’s called Simplified Payment Verification.  The lightweight client can send and receive transactions, it just can’t generate blocks.  It does not need to trust a node to verify payments, it can still verify them itself.

The lightweight client is not implemented yet, but the plan is to implement it when it’s needed.  For now, everyone just runs a full network node.

I anticipate there will never be more than 100K nodes, probably less.  It will reach an equilibrium where it’s not worth it for more nodes to join in.  The rest will be lightweight clients, which could be millions.

At equilibrium size, many nodes will be server farms with one or two network nodes that feed the rest of the farm over a LAN.