Unexpectedly, MS-DOS 2.0 included a /dev directory.

https://github.com/microsoft/MS-DOS/blob/main/v2.0/source/CO...

Traditional reference how Microsoft was doubling down on UNIX with Xenix, before having a change of heart.

The Future of Xenix, Bill Gates Interview on Unix World, back in 1985

https://archive.org/details/Unix_World_Vol02_10.pdf

I was teaching myself 8086 16-bit assembly a few nights ago on MS-DOS 5.0. It was so much fun getting a color block to display on CGA.

Nevertheless, writing system code in assembly was probably going to cause a lot of insomnia and other side effects, especially when Microsoft was far from the domination force on IBM PC.

This is enlightening. Growing up playing with Unix boxes (and XENIX, specifically, mostly writing shell scripts and playing in the filesystem) and programming MS-DOS in assembly I could often see strange parallels between how stuff worked in MS-DOS and his stuff was in Unix. I just assumed MSFT programmers had used Unix at some point and wanted to lift features and idioms from it to use in DOS. It never occurred to me, knowing XENIX was a MSFT-licensed Unic derivative, that there might be more direct inspiration in that vague Unix "flavor" in DOS.

I never did any CP/M programming, so the whole FCB-based file manipulation API in MS-dos just seemed like strange old cruft to me. Had I been exposed to CP/M the Unix inspiration behind the handle-based API would have been a lot more apparent. (I got in about the MS-DOS 3.3 timeframe...)

What a strange world it would have been in MSFT got IBM to buy into the Unix path separator.

I know this is software focused, but as much of the work done in DOS 2.0 was to support the introduction of hard disks, it would be worth mentioning what the hardware was in the PC/XT:

https://en.wikipedia.org/wiki/ST-506/ST-412

https://www.google.com/search?client=firefox-b-d&q=ST-212+ha...

>Even a scaled-down version of Unix was too demanding for the 8086 chip”.

Interesting. At my old job I got my hands on Wang IN/ix around 1985, a 16 bit UNIX.

It ran on an 8086 but needed 512k memory. It ran fine. I wonder if memory was the main issue ? But seems the issue was probably memory for IBM and MS

>"But it soon became clear that IBM was committed to keeping DOS 2.0 as close as possible to the eight thousand bytes [8K] used by DOS 1.1, so as not to disrupt their existing user base. [...] The first version of MS-DOS 2.0 shipped with IBM PC XT as PC-DOS 2.0 on March 8, 1983. It required about 20 KB of RAM, far more than MS DOS 1.0, so both versions continued to be sold simultaneously for a while."

And that approximate doubling, in RAM requirements, year by year (compare to Moore's Law for hardware!) for Microsoft's OS'es, has got us, fellow students of computer history, to where we are today -- with Microsoft OS'es being the size that they are and requiring the RAM that they do!

And it all started with upgrading (or "upgrading", take your pick of term!) an 8KB OS to a 20KB OS! :-)