The problem with IOCP is that it is more memory intensive as all memory for outstanding operations must be pre-allocated. With the readiness model, you can use

The problem with IOCP is that it is more memory intensive as all memory for outstanding operations must be pre-allocated. With the readiness model, you can use pools of memory instead for dramatically less overall memory usage. There is a hack to use 1B reads with IOCP to get around this, but it doesn't feel very clean.