By allowing the CPU, peripheral processors (PPs) and I/O to operate in parallel, the design considerably improved the performance of the machine. Under normal conditions a machine with several processors would also cost a great deal more. Key to the 6600's design was to make the I/O processors, known as "peripheral processors" (PPs), as simple as possible. The PPs were based on the simple 12-bit CDC 160-A, which ran much slower than the CPU, gathering up data and transmitting it as bursts into main memory at high speed via dedicated hardware.