Category Archives: DOS

Another Myth Busted

Posted on January 19, 2022 by Michal Necasek

More than once I came across a story of a heroic MicroPro programmer who in an all-night session managed to port WordStar from CP/M to DOS by patching a single byte. This is how the legend was retold by Joel … Continue reading →

Posted in CP/M, DOS, PC history, WordStar | 5 Comments

Unidentified PC DOS 1.1 Boot Sector Junk Identified

Posted on January 7, 2022 by Michal Necasek

Anyone trying to disassemble the PC DOS 1.1 boot sector soon notices that at offsets 1A3h through 1BEh there is a byte sequence that just does not belong. It appears to be a fragment of code, but it has no … Continue reading →

Posted in Development, DOS, PC history | 24 Comments

DOS 2.11 From Scratch

Posted on September 21, 2021 by Michal Necasek

Warning: Long post! After having good luck with rebuilding core PC DOS 1.1 from source code, I thought I’d do the same with the DOS 2.11 source code released by the CHM. What follows is largely a collection of notes … Continue reading →

Posted in Development, DOS, Microsoft, PC history | 42 Comments

PC DOS 1.1 From Scratch

Posted on September 10, 2021 by Michal Necasek

A number of years ago, the Computer History Museum together with Microsoft released the source code for MS-DOS 1.25 (very close to PC DOS 1.1) and MS-DOS 2.11. I never did anything with it beyond glancing at the code, in … Continue reading →

Posted in Development, DOS, Microsoft, PC history | 24 Comments

PC-86-DOS

Posted on September 3, 2021 by Michal Necasek

A number of years ago, an 8″ disk containing Seattle Computer Products (SCP) 86-DOS 1.0 was successfully imaged. The newest files on the disk are dated April 30, 1981, making the disk the oldest complete release of what was soon … Continue reading →

Posted in Development, DOS, IBM, PC history | 18 Comments

How Not to Erase Data

Posted on August 16, 2021 by Michal Necasek

From past blog posts it is fairly obvious that the OS/2 Museum occasionally purchases used hard disks. Most of the time, the disks are either completely erased (overwritten with zeros) or don’t have anything very interesting on them. But sometimes … Continue reading →

Posted in DOS, PC hardware, Storage | 17 Comments

The IBM PC, 41 Years Ago

Posted on August 10, 2021 by Michal Necasek

No, the OS/2 Museum does not have either a time machine or difficulty doing basic math. As of this writing, it is August 2021 and the IBM PC was announced in August 1981, 40 years ago. But in August 1980, … Continue reading →

Posted in 8086/8088, BIOS, DOS, IBM, Intel, PC hardware, PC history | 60 Comments

DOS SMB Client Performance

Posted on May 20, 2021 by Michal Necasek

Recently I had the need to use several different DOS VMs that all used a SMB network client. Although I did not use networking heavily, I noticed that there are massive differences in performance between the VMs. Copying a circa … Continue reading →

Posted in DOS, IBM, Microsoft, Networking | 15 Comments

It Was a Problem Back in the Day

Posted on May 19, 2021 by Michal Necasek

Several years ago, I found out the hard way that old versions of DOS have trouble with hard disks with more than 17 sectors per track. To recap, DOS versions older than 3.3 may hang when booting from a hard … Continue reading →

Posted in Bugs, DOS, ESDI, Storage | 26 Comments

MS LAN Manager NDDK Anyone?

Posted on April 2, 2021 by Michal Necasek

For R&D purposes, I would very much like to get my hands on the circa 1991 Microsoft LAN Manager Network Device Driver Kit which was meant to support the development of NDIS 2.0 drivers. While it is obvious that some … Continue reading →

Posted in Development, DOS, Microsoft, Networking, OS/2 | 10 Comments