hello, I see http://simh.trailing-edge.com but i can't work with similator of 2100. i have hp 2100S computer and hp 7900A disc drive. i haven't backup heads of 7900a and i want provide them. i have some program in exe format on 7900A disc,i want run them on pc but i don't know any way for run them on pc. i study about CPU,DMA,I/O system of hp 2100 and 7900A disc drive too. i doing work now to make my designed I/O circuit ,it input in pc's ISA and work like 7900A for 2100S 's I/O associate disc, but some work remain to complet this subject. i want write assemblly program (and input in memory of 2100) for read sector by sector data of 7900A with selected code 0 and write them on my I/O with selected code 1 and write another C program on pc for work with I/O and file this data. i think that if i can do it i shall write similator program and when decode I/O instruction with DMA,disc drive I/O selected code load addressed data in file to array (virtual RAM)in similator program. but i know that i need help very much. i don't know many things about your similator , i hope possible that i can work with your similator and run my 2100 program on similator. please send me any information that you think it is good. please help me. my name is mehdi . my email : oceanid987(a)yahoo.com __________________________________ Do you Yahoo!? Protect your identity with Yahoo! Mail AddressGuard http://antispam.yahoo.com/whatsnewfree