CP/M pages
Home -> CP/M -> DOS Plus mini-howto

DOS Plus mini-howto

The files

DOS Plus 1.2 (CP/M-86 v4.1) is available for download from the Web.

Its boot floppy is here; if you want to boot it from a hard drive you will also need this zipfile of utilities.

How to install

DOS Plus 1.2 does not understand floppies bigger than 360k, and the only hard drive partitions it supports are DOS-formatted ones smaller than 32Mb. So, if you want to install it on your hard drive you may well have to do some serious partitioning.

It will boot in the Linux DOS emulator as long as you have two or fewer emulated hard drives. It will crash on booting if there are three or more.

I have written a modified XIOS which adds support for 720k and 1.4Mb floppies, and hard drive partitions up to 512Mb or so. It also works on a system with more than two hard drives.


DOS Plus 1.2 was one of Digital Research's first DOS clones. It supports:

The documented APIs of PCDOS 2.11.
Documented is the operative word. None of the internal calls is supported (retrieve the InDOS flag etc.) and only programs which are written in a well-behaved manner will work. GEM does; so do Anadisk and Teledisk. PKZIP (and many other programs in .EXE format, including any compiled with Pacific C) won't even run - see DOS Plus EXE Loader for the full details.
The DOS emulation works by making CP/M-86 API calls. The CP/M part will run happily without the DOS part - see CP/M-86 versions for more details.
The complete CP/M 4.1 API. Limited preemptive multitasking for CP/M-86 programs.
The multitasker allows up to three CP/M-86 programs to be run in the background, with one CP/M-86 or DOS program in the foreground.
The CP/M 4 API is similar to CP/M 3, with the addition of dynamic linking of RSXs, the ability to set a file's date stamps, and proper memory allocation code.
Transparent access to CP/M and DOS filesystems
Both CP/M and DOS programs can access the supported CP/M and DOS filesystems. Exact file lengths are supported on both media, but passwords only on CP/M media. Subdirectories can be used by CP/M-type and DOS-type programs.
Dual-boot support.
Supports dual-booting with other DOS versions. Rename the supplied COMMAND.COM to DOSPLUS.COM, and use the %OS% variable in AUTOEXEC.BAT. DOS Plus does not use CONFIG.SYS. Instead of the two system files IBMBIO.COM / IBMDOS.COM, there is one file (DOSPLUS.SYS) which is in CP/M-86 .CMD format. The dual-boot program is FIXLDR.COM, and should be run from the root of C:.

Return to archive listing