19 Feb
2009
19 Feb
'09
6:27 p.m.
There was also the NEC V20, which was pin for pin compatible with the
8088. It was a CMOS part. There were a few instructions that the V20
executed in fewer clock cycles than the 8088 (multiply comes to mind),
causing some motherboard vendors to install a V20, and the sell a 10mhz
motherboard as a 12mhz motherboard.
The truly great feature of the V20 was the 8080 emulation mode. When a
special opcode was executed, the processor switched to 8080 mode, a very
fast 8080. I made several CP/M (80) systems using a V20 processor, with
a small prom to put the v20 into 8080 mode. I could then switch back
into 16 bit mode to implement a ram disk.
Les