CP/M Plus (CP/M Version 3.1)

Abstract

Now that memory is very cheaply and easily available for microcomputers it is noticeable that, as each year goes by, the size of memory commonly installed increases by a factor of two. At present 64K of RAM is the norm for the 8-bit micro and the step up to 128K has produced a problem. An 8-bit processor cannot address, directly at least, more than 64K. This is because the largest integer that can be stored in a Z80 processor address register of 16 bits is 65535 in decimal notation, or FFFF in hexadecimal. 65535 is in fact 64 times 1024 minus 1; 1K being, of course, 2 to the power 10, not 1000.