Supporting the CPU were ten 12-bit 4 KiB peripheral processors (PPs), each with access to a common pool of 12 I/O channels, that handled input and output, as well as controlling what data were sent into central memory for processing by the CP. The PPs were designed to access memory during the times when the CPU was busy performing operations. This allowed them to perform input/output essentially for free in terms of central processing time, keeping the CPU busy as much as possible.