One of my recent time sink-hole projects is de-compiling DOS 1.1. I figure that I needed a computing challenge :) Anyway, this plus a message from one of our own, results in an interesting question. How, in 1982 (or in 1980-81, when Project Acorn was in beta), would Microsoft have written and compiled DOS 1? I know that DOS as we know it was purchased from Tim Patterson of Seattle Computing Products (Is this the right name? I don't have a copy of one of my many Gates books handy.), so the source code in printed, magnetic, or paper tape form would have existed. Would they have used a PC simulator running on another computer (the same way they wrote BASIC for the Altair)? Would they have waited to receive a beta unit to test/develop it live after months of writing blind code based on IBM's specifications documents? Anyway, I digress. I've pretty much finished the boot sector code, and IBMBIO is done. So, now I'm working on IBMDOS. Does anyone know anything about how early DOS versions loaded? Looking at the DOS1 code and comparing it to DOS6 code, it seems like the DOS1 boot sector loads both BIO and DOS back-to-back in memory (producing a single image, if you will), and then jumps to BIO. DOS6, in comparison, the boot sector loads IO, which then loads DOS. Any thoughts? I felt this qualifies as "classic" since the file dates are May 7, 1982 <g> Rich Cini/WUGNET &lt;nospam_rcini(a)msn.com&gt; - ClubWin! Charter Member - MCP Windows 95/Windows Networking - Preserver of "classic" computers <<<< ========== reply separator ========== >>>>>