CP/M: The first multi-platform standard


CP/M (Control Program/Monitor) was the most universal
monitor/disk operating system for 8080/Z80 systems
before MS-DOS/PC-DOS took over the world.

The BIOS abstraction layer allowed binary only programs
to run on different hardware variations.

That led to killer apps such as
  1. Wordstar
  2. VisiCalc
  3. Multiplan
  4. Games & Entertainment

Of course, many made their own proprietory system such as
  1. Tandy/Radio Shack's TRS-DOS
  2. Zilog RIO, RIO/CP monitor
There are open source systems such as UZI.

CP/M was a world to itself
with advocates such as Sol Libes
and the ACGNJ: Amateur Computer Group of New Jersey
that created the the SIG/M Software Library.

User groups and shareware
(such as the ACGNJ SIG/M archive on The Walnut Creek CP/M archive)
was a BIG PART of CP/M's popularity and success.

Z80 add-on retrofit cards were a way to keep running CP/M on other platforms:

Micro Solutions UniDOS is an 8 bit ISA card with 8 Mhz z80, 64k ram running CP/M on the IBM-pc


Released on April 2, 1980 as Microsoft's first hardware product,
the Microsoft Z80 softcard ran CP/M natively on the Z80 albeit inside an Apple ][.
the Microsoft Softcard III for the Apple /// computer is very rare.