Disc Operating System, started as 16-bit OS for PC-AT/XT x86++ platforms

Operating system for PC-AT/XT x86++

  • mostly known was MS-DOS from Microsoft but also other clones surface's
  • manages first 1MB of memory (20bit segmentated addressing from i8086/8088++)
  • 640KB for programs
  • rest for system, drivers
  • memory above 640KB was accessible only by drivers
  • himem.sys - access to 640-1024 KB
  • emm386.sys or qemm386.sys - access to 1-64 MB (XMS memory)
  • support for 2 FDD FAT11
  • HDD with FAT16 support
  • natively it uses text video modes on CGA/EGA/VGA 80x25 characters
  • support these file extensions
  • *.sys - driver
  • *.com - executable fitted inside single 64KB segment
  • *.exe - executable with more segments