{"id":153,"date":"2024-01-05T18:39:00","date_gmt":"2024-01-05T18:39:00","guid":{"rendered":"https:\/\/thebrokenpipe.com\/blog\/?p=153"},"modified":"2026-04-26T12:30:32","modified_gmt":"2026-04-26T12:30:32","slug":"86-dos-0-11-ibm-pc-port","status":"publish","type":"post","link":"https:\/\/thebrokenpipe.com\/blog\/86-dos-0-11-ibm-pc-port\/","title":{"rendered":"86-DOS 0.11 – IBM PC Port"},"content":{"rendered":"\n
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<\/path><\/svg>Update<\/p>\n

This port is now outdated<\/u>. The latest ports of 86-DOS to the IBM PC are on GitHub<\/a> and binaries may be downloaded from there too.<\/p>\n<\/div>\n\n\n\n

This is not a writeup, the port is still WIP. I’m just dumping whatever I’ve done here for people to see, because xmas and new year holidays are now over and I don’t want to devote any more of my very limited free time to projects like this.<\/p>\n\n\n\n

A few days ago, Gene Buckle<\/a> uploaded 86-DOS 0.11<\/a> and 0.34<\/a> to the Internet Archive<\/a>. After about 2 hours of coding and debugging, perhaps the oldest surviving piece of x86 software booted on the (emulated) IBM PC:<\/p>\n\n\n

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\"\"<\/figure>\n<\/div>\n\n\n\n\n\n\n

I didn’t do anything too fancy – just modified the BIOS from my 86-DOS 1.14 port<\/a> to simulate 128-byte sectors. As with my 1.14 port, I patched the kernel to use PC-DOS’ special editing commands, patched RDCPM<\/code> to read CP\/M-86 disks and rewrote SYS<\/code>.<\/p>\n\n\n\n

Everything works, but it is slow as a sloth. To workaround the stack overflows, I made the BIOS switch to an internal stack for every single call. Also, I did not implement buffered I\/O – sequential reads are 4 times slower and sequential writes are 8 times slower (though I do have experimental buffered disk reading code).<\/p>\n\n\n\n

If you’re interested in improving my code or implementing proper buffered I\/O, drop a comment here and I can send you my BIOS source code.<\/p>\n\n\n\n

Random note: 86-DOS 0.11’s FCB search function returns a 16-byte directory entry, rather than an unopened FCB. This makes its COMMAND.COM<\/code> misbehave under later DOS versions.<\/p>\n\n\n

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\"\"<\/figure>\n<\/div>\n\n\n

Last thing – I have a plan to reconstruct the source code of 86-DOS 0.11, because this version is historically significant, it’s the earliest version of DOS (apart from QDOS 0.10, which was never released). I have already disassembled some binaries, but they’re really just the low hanging fruits like COMMAND.COM<\/code>, SYS.COM<\/code> and HEX2BIN.COM<\/code>. If you have experience reverse engineering 8086\/DOS code, please consider helping out, thanks!!<\/p>\n\n\n\n

Edit: It’s been a week, I’ve contacted a few people and nobody is willing to lend a hand. I’m just going to reup the binaries with IO.ASM<\/code> and SYS.ASM<\/code>. If you’d like to contribute, go ahead and use these sources!<\/p>\n\n\n\n

WIP PC port + COMMAND.COM<\/code>, SYS.COM<\/code> and HEX2BIN.COM<\/code> src: https:\/\/mega.nz\/file\/4EZ2kLCB#pNJ4iRM2DqsQ9YJ9oAZWTsn4DLy0dH3LpsRdJDCel6U<\/a>
<\/s><\/p>\n\n\n\n

Edit 2: With IO.ASM<\/code> and SYS.ASM<\/code>:<\/s> https:\/\/mega.nz\/file\/JZpUBRKL#0ANcb2NKVELClamu0kRZknhl4WrHhXn7r_df9NabPXY<\/s><\/a>
<\/p>\n\n\n\n

Edit 3: PC port<\/a> and source code reconstruction<\/a> are now on GitHub.<\/p>\n","protected":false},"excerpt":{"rendered":"

Update This port is now outdated. The latest ports of 86-DOS to the IBM PC are on GitHub and binaries may be downloaded from there too. This is not a writeup, the port is still WIP. I’m just dumping whatever I’ve done here for people to see, because xmas and new year holidays are now […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5,6],"tags":[],"class_list":["post-153","post","type-post","status-publish","format-standard","hentry","category-dos","category-reverse-engineering"],"_links":{"self":[{"href":"https:\/\/thebrokenpipe.com\/blog\/wp-json\/wp\/v2\/posts\/153","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/thebrokenpipe.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/thebrokenpipe.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/thebrokenpipe.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/thebrokenpipe.com\/blog\/wp-json\/wp\/v2\/comments?post=153"}],"version-history":[{"count":5,"href":"https:\/\/thebrokenpipe.com\/blog\/wp-json\/wp\/v2\/posts\/153\/revisions"}],"predecessor-version":[{"id":263,"href":"https:\/\/thebrokenpipe.com\/blog\/wp-json\/wp\/v2\/posts\/153\/revisions\/263"}],"wp:attachment":[{"href":"https:\/\/thebrokenpipe.com\/blog\/wp-json\/wp\/v2\/media?parent=153"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/thebrokenpipe.com\/blog\/wp-json\/wp\/v2\/categories?post=153"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/thebrokenpipe.com\/blog\/wp-json\/wp\/v2\/tags?post=153"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}