Concurrent CP/M - Multiplies the power of your microcomputer

Digital Research had been set up in 1976 to capitalise on the popularity of Gary Kildall's CP/M operating system - the popular and de-facto standard OS for most serious microcomputers during the 1970s.

The company suffered a major setback though when CP/M was cloned by Seattle Computer Products and eventually found its way to Microsoft, which sold it to IBM for its new 5150 IBM PC in 1981, where it was known as PC-DOS. Microsoft retained the rights to sell this to other companies, which it did as MS-DOS.

Although IBM offered CP/M as an option, it set the price to $240 (about [[160|1981]] in [[now]]), which didn't compare well to the $40 it was offering PC-DOS for[source: https://www.theregister.com/2022/08/04/the_many_derivatives_of_cpm/].

CP/M was originally written for Intel's 8080 processor, but was ported to the Z80 when that was released as a clone of the 8080. Being a lot cheaper, the Z80 became hugely popular and its success effectively dragged CP/M along for the ride.

After the advent of the IBM PC and its clones, which ran on the Intel 8086 or 8088, Digital ported its multi-user variant MP/M onto the new chip. It then merged this with the 8086 version of CP/M - CP/M-86 - to create Concurrent CP/M, the multi-user, multi-tasking OS of the advert.

This effectively turned the host PC into a minicomputer, capable of supporting several users connected via RS-232 terminals. Even without the multi-user aspect, Concurrent CP/M's multi-tasking ability was well ahead of MS-DOS, which didn't get proper multi-tasking support until MS-DOS 4.0 in 1986, three years later.

The OS's Achilles heal is mentioned in the advert where it states that it "lets you use all the CP/M compatible programs". This, unfortunately, didn't refer to the huge back-catalogue of Z80-based CP/M software, but only that written for CP/M-86, of which there wasn't a huge amount.

DR ended up having to develop a "PC Mode" which allowed MS-DOS 1 software to run on Concurrent CP/M. This was released the following year as Concurrent DOS.