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OS family CPM Working state Discontinued Source model Closed source Final release 7.22 R18 21 April 2005; 15 years ago ( 2005-04-21 ) (REAL32: 7.95) Available in English Platforms x86, 68000 Kernel type Monolithic kernel Default user interface Command-line interface ( COMMAND.COM ) License Proprietary Official website Various (see notes).

It was commercially unsuccessful as IBM s PC DOS 1.0 offered much the same facilities for a considerably lower price.

Like PC DOS, CPM-86 did not fully exploit the power and capabilities of the new 16-bit machine.

This turned a PC into a multiuser machine capable of supporting multiple concurrent users using dumb terminals attached by serial ports.

The environment presented to each user made it seem as if they had the entire computer to themselves.

Since terminals cost a fraction of the then-substantial price of a complete PC, this offered considerable cost savings, as well as facilitating multi-user applications such as accounts or stock control in a time when PC networks were rare, very expensive and difficult to implement.

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These machines had both 16-bit and 8-bit processors, because in the early days of 16-bit personal computing, 8-bit software was more available and often ran faster than the corresponding 16-bit software.

Concurrent CPM-8680 allowed users to run both CPM (8-bit) and CPM-86 (16-bit) applications.

When a command was entered, the operating system ran the corresponding application on either the 8-bit or the 16-bit processor, depending on whether the executable file had a.COM or.CMD extension.

It emulated a CPM environment for 8-bit programs by translating CPM system calls into CPM-86 system calls, which were then executed by the 16-bit processor.

Pedrizetti, Dave Brown and Gordon Edmonds teamed up to create PC-MODE, 12 an optional module for Concurrent CPM-86 3.1 13 14 (with BDOS 3.1) to provide basic compatibility with PC DOS 1.1 (and MS-DOS 1.1 ).

This was shown publicly at COMDEX in December 1983 12 and shipped in March 1984 as Concurrent DOS 3.1 (a.k.a.

CDOS with BDOS 3.1) to hardware vendors.

For example, although a console program such as PKZIP worked perfectly and offered more facilities than the CPM-native ARC archiver, applications which performed screen manipulations, such as the WordStar word processor for DOS, would not, and native Concurrent CPM (or CPM-86) versions were required.

Holsworth (using siglum FRH).

Concurrent DOS 68K 1.0 became available for OEM evaluation in early 1985.

The effort received considerable funding worth several million dollars from Motorola 20 and was designed for their 68000 68010 processors.

Like the earlier GEMDOS system for 68000 processors it initially ran on the Motorola VME 10 development system.

Concurrent DOS 68K 1.201.21 was available in April 1986, 22 23 24 offered for about 200 000 dollars to OEMs.

This system evolved into FlexOS 68K in late 1986.

This was based on MPM-286 and Concurrent CPM-286, on which Digital Research had worked on since 1982.

The release of Concurrent DOS 286 had been scheduled for late May, but was delayed until Intel could develop a new version of the chip.

In August, after extensive testing E-1 step samples of the 80286, Digital Research said that Intel had corrected all documented 286 errata, but that there were still undocumented chip performance problems with the prerelease version of Concurrent DOS 286 running on the E-1 step.

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Intel said that the approach Digital Research wished to take in emulating 8086 software in protected mode differed from the original specifications; nevertheless they incorporated into the E-2 step minor changes in the microcode that allowed Digital Research to run emulation mode much faster (see LOADALL ).

This ran on machines equipped with the Intel 80386 and later processors, using the 386s hardware facilities for virtualizing the hardware, allowing most DOS applications to run unmodified under Concurrent DOS 386, even on terminals.

The OS supported concurrent multiuser file access, allowing multiuser applications to run as if they were on individual PCs attached to a network server.

Concurrent DOS 386 allowed a single server to support a number of users on dumb terminals or inexpensive low-specification PCs running terminal emulation software, without the need for expensive workstations and then-expensive network cards.

It was a true multiuser system; several users could use a single database with record locking to prevent mutual interference.

It required its own special device drivers for much common hardware, as PC DOS drivers were not multiuser or multi-tasking aware.

Driver installation was more complex than the simple PC DOS method of copying the files onto the boot disk and modifying CONFIG.SYS appropriately it was necessary to relink the Multiuser DOS kernel (known as a nucleus ) using the SYSGEN command.

Although many of these were soon rectified for example, graphical terminals were developed, allowing users to use CGA, EGA and VGA software it was less flexible in this regard than a network of individual PCs, and as the prices of these fell, it became less and less competitive, although it still offered benefits in terms of management and lower total cost of ownership.

As a multi-user operating system its price was higher than a single-user system, of course, and it required special device drivers, unlike single-user multitasking DOS add-ons such as Quarterdecks DESQview.