Xenix was Microsoft's first operating system, it predates DOS.
Admittedly, Microsoft did not actually write Xenix. They bought a System3 source license from AT&T and used that as a base, Their main service model was to port it to various systems.
Fun Fact: Xenix was the main reason a partition table was included when the PC first got hard disk support.
During 1977 and 1978, Microsoft adapted both BASIC and Microsoft
FORTRAN for an increasingly popular 8-bit operating system called
CP/M. At the end of 1978, Gates and Allen moved Microsoft from
Albuquerque to Bellevue, Washington. The company continued to
concentrate on programming languages, producing versions of BASIC for
the 6502 and the TI9900.
During this same period, Marc McDonald also worked on developing an 8-
bit operating system called M-DOS (usually pronounced "Midas" or "My
DOS"). Although it never became a real part of the Microsoft product
line, M-DOS was a true multitasking operating system modeled after the
DEC TOPS-10 operating system. M-DOS provided good performance and,
with a more flexible FAT than that built into BASIC, had a better
file-handling structure than the up-and-coming CP/M operating system.
At about 30 KB, however, M-DOS was unfortunately too big for an 8-bit
environment and so ended up being relegated to the back room. As Allen
describes it, "Trying to do a large, full-blown operating system on
the 8080 was a lot of work, and it took a lot of memory. The 8080
addresses only 64 K, so with the success of CP/M, we finally concluded
that it was best not to press on with that."
I was always curious on why their original product, BASIC, did not evolve into a full operating system. Looking at it with the sensibility of a unix affectionado. basic is sort of analogous to the unix shell, a unified interactive user interface and scripting language. This would appear to be a far superior interface than the relatively crippled CP/M inspired DOS command interpreter.
My best guess, memory, on those early microcomputers that consideration trumped any user interface ergonomics and DOS(cough CP/M) used less memory than the BASIC interpreter.
Xenix was Microsoft's first operating system, it predates DOS.
Admittedly, Microsoft did not actually write Xenix. They bought a System3 source license from AT&T and used that as a base, Their main service model was to port it to various systems.
Fun Fact: Xenix was the main reason a partition table was included when the PC first got hard disk support.
They developed something called M-DOS or MIDAS in 1979, but by that time CP/M was already established, so they decided against releasing it.
This was news to me, so I went digging.
« M-DOS
»
https://www.pcjs.org/documents/books/mspl13/msdos/encycloped...
I was always curious on why their original product, BASIC, did not evolve into a full operating system. Looking at it with the sensibility of a unix affectionado. basic is sort of analogous to the unix shell, a unified interactive user interface and scripting language. This would appear to be a far superior interface than the relatively crippled CP/M inspired DOS command interpreter.
My best guess, memory, on those early microcomputers that consideration trumped any user interface ergonomics and DOS(cough CP/M) used less memory than the BASIC interpreter.
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