HN Theater @HNTheaterMonth

DOS 2.0 was originally supposed to be a single-user version of Xenix. There were some undocumented options to make it more Unix-like, which were removed in later versions:

https://www.youtube.com/watch?v=Vo8NG8T4rWs

The connection with Xenix is also pretty clear from the file names and comments in the released source code:

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

⬐ PopAlongKid

I don't need to watch the video to know that two of these options were entries in CONFIG.SYS, one of them "SWITCHAR" as I recall. It would cause DOS to use forward slash instead of backslash for separating components of a pathname, and it would use hyphens instead of forward slashes for command line options, both just like Unix.

⬐ rep_lodsb

You are correct, and the other one is AVAILDEV. Set it to false, and device names like CON only refer to the device when prefixed with "/dev/".

Microsoft did have a reason to remove these features: compatibility with batch files.

"\dev\" actually remained special in all later versions, in that it can always be used to open a device, even if that directory doesn't exist. This could break a common idiom in batch files to test if a path is valid:

C:\> if exist \dev\nul echo Yup, still there

(I don't have a recent version of Windows to test this on, interested to see if it still works!)

⬐ ksaj

I didn't realize switchar was undocumented. I learned initially on QNX so the /args used to drive me nuts. So needless to say, I used that one.

I'm pretty sure though that I learned about it straight from the DOS manual, which was a 2-ring binder with a LOT of pages in it. I learned Assembler from its surprisingly detailed chapters on the DEBUG command. (Needless to say, MASM and TASM were godsends once I discovered them!)

AVAILDEV is completely new to me though. That one I'm pretty sure wasn't in the manual, because it also seems like one I would have naturally gravitated to.

Great video. Blast from the past with something "new" besides.

BTW: You could put CON in any directory name and it would reference the console just the same. It didn't matter if it was \DEV\CON or \BANANA\CON, it worked just the same. There were a few pranks played using this "device" quirk.

There was also that XEDOS, that never officially saw the light of day. But some of those feature apparently made it into MS-DOS 2.x and appear as those *nix-like features that DOS had from 2.0+.

https://youtu.be/Vo8NG8T4rWs

⬐ skissane

> There was also that XEDOS, that never officially saw the light of day

I wonder if XEDOS ever existed as actual code, as opposed to simply an item in a roadmap.