This was the first computer to use IBM's seminal and widely-used Microprocessor board. So called because of its use of microcode to reduce the amount of circuitry required, this was one of the first, and certainly the most popular implementations of the idea of implementing an entire CPU on a single board. The CPU was six-bit and shared some op-codes with the IBM 360 instruction set, though it was also optimised for FORTRAN. There was space inside the case for up to 4 Kw of RAM, the ROM being mapped onto a different memory area. There was a 5" CRT-based monitor built in with the option of using an external monitor, which could be switched between black on green and green on black, and a tape drive using IBM's seven track system.