< I would _guess_ that MS-DOS was written and assembled on a CP/M system of < some sort, until it was self-hosting. Although, it's also quite possible < that MS-DOS was assembled on a QDOS system, since that's basically what < it was :) it could have been done under intel ISIS using the MDS-311 package or IRMX-80 or IRMX-86 along with ICE pods. the 8088/86 was a already a mature product by time IBM started the PC and there wre at least three second sources. Also 8086 development tools from Intel, AMD and HP to name a few were available. So developing 808x code was not a problem. I know that as we built a system using 8088 at 8mhz to play with the 7220 GDC which was the hottest thing for graphics on one chip for before the PC would escape into the world. Allison