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Altered Dos 2.x (?) versions

Fox-1 / mnx

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Since lot's of years I've these unofficial DOS versions laying around. From the looks I'd say all of them are modified DOS 2.x ones. Many have probably encountered those but is there actually anyone know what the mods are all about? There must be a reason someone decided to modify them but since they came without docs I've no clue what they're trying to accomplish.


So, just out of curiosity, does anyone have some info about below versions?



DOS 2.1C




DOS 2.1P




DOS 2.6F




DOS 2.8F



post-3660-0-61998200-1454854461_thumb.jpg post-3660-0-96052500-1454854478_thumb.jpg

DOS 2.75






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I remember Long John's Dos - it came out fairly early on. One modification is that the Duplicate Disk function does a full copy rather than by allocation bitmap like most Dos-based duplicators.

That said of course it didn't really offer anything revolutionary though does have that RPM check which isn't exactly common.


K-Dos, fairly sure it's a standalone product, from K-Byte, the same software house that released games like Krazy Kritters.

The revolutionary thing about K-Dos is it's got a command wedge - you can issue commands from Basic or the active language processor simply by prefixing them with a comma. Not sure if any other Doses ever made had that feature (I imagine it's implemented by means of an E: redirect).


I don't think they ever continued development though... that's a common story with a lot of the 3rd party Doses. Once enhanced density came along a lot of them didn't upgrade their products to properly support it (to say nothing of lack of real DD support).

Edited by Rybags
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All the DOS 2 DUP versions with options A - T are (more or less) the same, DUP.SYS has a length of 76 sectors. Since DOS 2.0 did not copy boot sectors when duplicating a disk, this was the DOS (or tool) that did it back then. Its older than most sector copy programs - not sure who the original author was, but most others seem to have only changed the colour, title and version number, like e.g. DOS 2.1c, DOS 2.5f, DOS 2.6f, DOS 2.8f, DOS 4.0 (really!), DOS 8.0, etc. its always DOS.SYS with 39 sectors (DOS 2.0s) and then DUP.SYs with 76 sectors (one could also copy it onto a disk with DOS 2.5, so that DOS.SYS has 37 sectors and DUP.SYS has 76 sectors; the same was done with Rainbow DOS - copied on a DOS 2.0 or DOs 2.5 disk and then named DUP.SYS)...


DOS 2.75 was originally named DOS 2.71 and was a bug-fixed version from an east-german A8 user (former GDR). He fixed 13 or more serious DOS 2.5 bugs and named the result DOS 2.71, I simply changed it to DOS 2.75 to make clear that it originated from DOS 2.5 (and already have renamed it to DOS 2.5 again). It also supports a bigger ramdisk with up to 256k XRAM (320k total RAM) and a new ramdisk driver - this new RD driver does however not work with original DOS 2.5 by Atari, only with the fixed version. There is a german manual available that describes the bugs in detail. Think you can download it from the Abbuc PD library with the german docs on diskette...

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All the DOS 2 DUP versions with options A - T are (more or less) the same


"More or less", indeed, but it's those small differences that's makes it interesting (well, apart from just color changes).


Someone invested a bit of time to do the mod and likely had a reason to do so, so it's nice to know what the mods are actually doing.

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I very often used 2.6f due to the fact it could copy sectors. So when I had a bad disk, I tried copy it with this, mark down all bad sectors and retry those a lot. Sometimes I got lucky and all sectors copied, which I could never have done with a disk copy. Also did this on protected software, then tried to find the routine that checked the sectors and edited that. Hacked quite a few games like this. I never managed Alternate Reality or the English Software Smash Hits packs (still would love to find the routine for that bad sector check)

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