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MS DOS Ver 1.0 did not have OS support for device drivers. DOS ver2 added support for device drivers in the config.sys file during boot with the "DEVICE=[path][filename][parameters]".

1. Did CP/M have OS support for device drivers?


2. Did DOS ver1 leave device drivers out, or was DOS v2 device support a new advancement over CPM?

The answer depends on the version.

CP/M 2.2 did not support any loadable device drivers. There simply was no provisioning to do that. Originally, the in-built device drivers were limited to storage, console, and serial drivers. The system vendor could extend the BIOS with new devices, but that was fixed during the system build and nothing was loadable on demand. (Some of the mechanisms described below were, however, back-ported into 2.2 and alike systems like MP/M)

CP/M 3.0 actually did support loadable system extensions (Resident System Extensions, RSX). These extensions were loaded resident into the computer and could extend the BDOS with new calls. A similar, but not identical expansion was GSX, a loadable extension to support graphical devices like terminals and printers, that itself relied on device-specific loadable drivers. These extensions implemented a standardized way of calling specific new vendor-defined system calls.

Some CP/M vendors, notably Amstrad/Sinclair (thus, Locomotive Software), implemented loadable system extensions on top of that - Amstrad/Sinclair CP/M 3.0 implemented a concept of FID (Field Installable Device drivers) that allowed extending the BIOS with support for new devices (hard disks or RAM disks, for example) without touching the original code. CP/M 3.0 for the ZX Spectrum 3 comes with a RAM disk driver as FID in source code, for example, that implements a drive M:.

Did CPM support custom hardware using device drivers?

Yes, of course, that's what the BIOS was for.

The title is somewhat misleading, as from the question body it seems you're asking about loadable device drivers, where loadable means that drivers where loaded at startup (or later) from separate binaries and linked into the system to offer their services. Further it seems as if the question is about CP/M prior to 1981, the time MS-DOS was introduced, thus CP/M 2.2 and MP/M. Right?

Did CPM have OS support for device drivers?

• Yes, as part of the customized BIOS.




• No, CP/M did not have loadable device drivers (*1).

All drivers where a part of the BIOS (Assembly) code. DR supplied sample code to customize the BIOS for system builders (Buyers of a non dedicated CP/M licence).

Adding new devices worked much the same way on CP/M and MS-DOS 1.x. In both cases new devices had to fit the existing structure of BIOS calls (17 for CP/M 2.2) (*2). New devices must be compiled into the BIOS (*3)

Did DOS ver1 leave device drivers out, or was DOS v2 device support a new advancement over CPM?

Loadable drivers where newly added to MS-DOS 2.0. To some degree it was part of the step toward a unixoid system structure for DOS, like adding subdirectories even including a virtual /dev directory for devices.

Except, it never went fully that way. Much was added (including IOCTRL), but device drivers still had to fit for most parts the existing structure, which wasn't always up to task. For the CD-ROM driver this meant that it had to hook itself as a network driver (introduced with DOS 3.1) and present the disk as a remote directory assigned to a drive letter instead of simply a disk.

*1 - There's a 'yes but' part: With GSX CP/M introduced loadable device drivers, much like MS-DOS 2.0, but that's after MS-DOS was created.

*2 - Another 'but': With MP/M and later CP/M 3.0 (CPM-Plus), the Character Device Table was introduced. Here an arbitrary number of character devices could be added by system builders, using 6 character names to identify them. Assignment to the logical devices was done using the DEVICE utility and controlled by according BIOS calls.

So while for block devices system builders had to assign a hard disk number to a new device, they could use sounding names for character devices. The default table size was 12 entries for each (In/Out), enabling limited run time extension within the existing structure.

*3 - It was possible (and done) to add new devices during run time by hooking the BIOS entry table and catching/redirecting calls for a drive. Unlike MS-DOS, CP/M did not provide a TSR functionality, so everything dynamic was up to detailed system knowledge and patching.

CPM 2.2, the most widely used and generally the progenitor of MS-DOS, supported only a few predefined devices via its BIOS.

These were:

• console input and output


• a listing device (printer) output


• a punch (presumable paper tape) output


• a reader (also paper tape) input


• various calls to control a mass storage device (floppy disk)

and that was that.

No loadable device drivers, even though there were a few terminate and stay resident style things, I have no references for those.

Generally, memory was so tight on these old machines that nobody wanted to load anything extra.

More info on the BIOS can be found here: CPM 2.2 Alteration Guide