taylor (03/25/83)
As Bill W. said, the iAPX286 is downward compatible with the iAPX86 (please note that the 80286 is the CHIP and the iAPX286 is the SYSTEM. Same goes for the iAPX86 versus the 8086) However, according to the Intel literature that I have obtained, the iAPX series are ALL compatible downward; iAPX286 < iAPX86 < iAPX88 <? 8085A/Z80A/Z80H/... IE: the 286 can run just about anything that you give it, since it has two addressing modes; real and virtual. In the real addressing mode, it can address 16 Mbytes (A LOT!!!!) so the old iAPX series software can be run in this mode 'without recompilation'. The problem with this is that you lose the data/memory protection features of the 286 system (not to men- tion the multi-user multi-tasking!!!). The alternative addressing mode is called virtual, and supports (better sit down for this one!) 1 TERRABYTE of virtual address space, with full HARDWARE user/program space integrity checking. (1 Terrabyte!!!!) It is in this mode that multi-tasking can occur, and Intel claims that a re-compilation is usually enough to get the old software working under Virtual. (Of course, they suggest that the code is massaged to take advantage of the extra capabilities...like the iAPX287 numerical processor, which makes the 286 system VERY comparable to the 11/780 ... ) I hope this helps. -- Dave Taylor