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
