CBIOS Technology from the Early Days

CP/M is organized into three parts: The CCP, the BDOS, and the CBIOS. The CCP is the Console Command Processor. This is the command line interface for CP/M. The BDOS is the Basic Disk Operating System, the heart of the disk file management part of the operating system. The CBIOS is the Customized Basic I/O System. It is the interface between the operating system and the microprocessor hardware.

There were 3 major releases of CP/M, and other than the changes that were incorporated for these different releases, the CCP and BDOS have remained fairly consistent. The functionality of the BDOS was expanded somewhat as CP/M evolved. Non-proprietary "drop-in" replacements for both have become available: most notably, ZCPR for the CCP, and ZRDOS for the BDOS.

The CBIOS is the most interesting part of CP/M because it contains everything necessary to make the local hardware congifuration function with the more standard CCP and BDOS. It is the interface between the microprocessor hardware and CP/M. In more current terms, it would probably be considered a collection of "drivers". But it also has the capability to start up, and restart, CP/M. Every vendor, that sold a CP/M system, had their own BIOS that was customized for their hardware. One of the biggest sources of variability in CBIOSes is the disk drive (usually two, or more, floppies). It is not uncommon to find 128-, 256-, 512-, or 1024-byte floppy disk sector sizes, and there are literally hundreds of CP/M diskette formats. The CBIOS has to translate the BDOS's requests for 128-byte logical "records" to physical disk parameters for the local disk drive, and serve as a buffer to aggregate these 128-byte "records" into physical disk sectors and unpack physical disk sectors into 128-byte "records".

The more astute CP/M hackers modified and customized their own CBIOS code, and in some cases, built their own homemade systems running with one-of-a-kind CBIOSes. So, the CBIOS reflects much of the creativity that was embodied in CP/M.

This part of the site is under construction and will change with time. I plan to put source code for old CBIOSes out here, as I have access to them.

What's Here

• Columbia M64 CBIOS from the CP/M CDROM.
• Generic BIOS as published by Andy Johnson-Laird in "The Programmer's CP/M Handbook"
• SVI-738 CBIOS kindly donated by Luis Claudio Grosso
• Montezuma Micro CBIOS (for TRS 80 mod. 4/4p running CP/M 2.2) kindly donated by Luis Claudio Grosso
• complete Montezuma Micro CP/M (thanks to Jeff Post)
• Otrona 500 CBIOS for CP/M 2.2
• S.D. Systems Stuff:
  • S.D.Systems ROM Monitor (2K).
  • S.D.Systems "Firmware" (2K).
  • Custom CBIOS that uses the "Firmware" above.
• Xerox Stuff:
  • XPro Software for the Emerald DD mod. for the Xerox 820-1 SBC.
  • Plus2 Firmware for the Emerald DD mod. for the Xerox 820-1 SBC.
  • Xerox CBIOS.
  • Macro library for CBIOS above.
• BIOS for the A.D.C. "Super Six" SBC (a single S-100 CPU card @ 6MHz).
• Spectravideo Stuff (thanks to Tomas Karlsson):
  • SVI-328 CP/M 2.24 CBIOS.
  • SVI-328 CP/M 2.2 A.P.
  • SVI-328 CP/M 2.2 C.U.C.
• CP/M for the MAI "luggable" CP/M box.
  • Entire CP/M O.S., including BIOS.
• Cromemco Stuff.
  • RDOS 2.52 ROM Monitor and Firmware.
  • CP/M System Generator (uses the following four files that contain CBIOS "drivers").
  • Console drivers for CP/M System Generator.
  • 3355 terminal drivers for CP/M System Generator.
  • Floppy drivers for CP/M System Generator.
  • Hard disk drivers for CP/M System Generator.
  • Cromemco screen editor for CDOS.
  • Cromemco disk/diskette formatter for CDOS.
  • Z80 Assembler (ver. 2.15) for CDOS.
  • Z80 Assembler (ver. 3.07) for CDOS.
  • Z80 Assembler (ver. 3.10) for CDOS.
  • Cromemco Asembler Manual. and manual cover
• CBIOS for the Disk Jockey 2D Controller.
• CBIOS for CP/M Plus (DJ2D cntrlr) Beta V1.2 11/1982 (thanks Howard!).
• CompuPro Stuff.
  • ROM based boot loader for a DISK1.
  • Disk based boot loader for a DISK1.
  • Sorcim CompuPro DISK1 CBIOS ver. 2.2J.
  • CBIOS for CompuPro CP/M 2.2q (thanks Howard!).
• Kaypro Stuff.
  • prelim. disassemb. of Kaypro II EPROM 81-149.
  • disassemb. of Kaypro II EPROM 81-232.
  • prelim. disassemb. of Kaypro 2 EPROM 81-292.
  • prelim. disassemb. of Advent TurboROM.
• ZDT debugger.
• AMPRO floppy disk formatter for CP/M.
• Digitex monitor for the Super6 SBC with disk image (thanks Howard!).
• A better dump CP/M app. (run with no args. to see all the goodies!).

Roger Hanscom

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