ZSOS (Z80 SBC OS) is a CP/M 3 distribution with a BIOS customized for the S100Computers.com Z80 Single Board Computer. John Monahan of the S100Computers.com website designed this board in late 2015 as a “starter board” for new users to “bootstrap” a new S-100 system from scratch. The S-100 Z80 SBC contains a Z80 CPU, ROM, RAM, an interface for an IDE drive or IDE→CF adapter, and a USB-based terminal. Typically in the past, these functions would have required a set of 3 S-100 boards - the Z80 CPU (w ROM socket), a RAM card, and a Serial I/O card.

For a complete description of the board including build instructions visit the S100Computers.com Z80 SBC Page.

For questions or discussion about this board or ZSOS, please visit the S100Computers Google Group - which John M. has kindly asked we used for all discussion related to the S100Computers.com boards.


These images are based on John Monahan's original CP/M 3 BIOS for the S100Computers Z80 CPU & IDE boards, with the addition of contributions by David Fry for the LBA addressing code, Dave Mehaffy (aka yoda) for details of image creation, and testing by the members of the S100Computers Google Group.


Latest/Current Version

ZSOS v0.11 (11-MAR-2016)

  • Non-banked CP/M 3
  • 44K Transient Program Area (updated!)
  • Includes support for a single drive on the CF card (A:)
    • User Area 0: CP/M 3 Base Files
    • User Area 1: <Reserved for future S100Computers board utilities folder>
    • User Area 2: SuperSoft Utilities
    • User Area 3: DDTZ Debugger (will need to be built from source)
    • User Area 4: BDS Tiny C
    • User Area 5: Games (new!)
    • User Area 6: Turbo Pascal 3.0 (new!)
    • User Area 7: Development Utilities updated!
    • User Area 8: <Available for additional user files> (updated!)
    • User Area 9: <Available for additional user files> (updated!)
  • Additional Changes
    • CPM3.SYS set to Read Only/System
    • CP/M 3 Base Files in User Area 0 set to System
    • Console Character I/O Routines (CHARIO3.ASM) updated to output all ASCII characters to the DLP USB Device. This fixes VT100 programs.
  • Latest Windows cpmtools included in the .zip, along with batch files and linux script to load User Areas 8 & 9

Old Versions

Writing to a CF Card

Extract the contents of the .zip to a new directory/folder. Write the 'zsos-0.10-02feb2016-base.img' file to a CF card - or alternately follow the instructions below to create an image with additional user files.

  • Windows: Win32DiskImager is the recommended way to write the image to a CompactFlast Card in Windows
  • Linux: The Linux dd command is the recommended way to write an image to a cf card in linux.


ZSOS is setup to be used with the DLP USB adapter on the Z80 SBC board, with the IOBYTE DIP switches set such that the Monitor ROM output goes to the USB device. Insert the CF card in your IDE→CF adapter, and press 'P' at the Monitor prompt to boot CP/M.

Adding additional files to the image

To add additional files to the image in User Area 5 and/or 6:

  • Windows: Add the files to be added the folders '5' and/or '6'. Run 'addusersfiles.bat'.
  • Linux: Ensure you have the cpmtools package installed. Add the text in the diskdef-s100ide file to the top of the file /etc/cpmtools/diskdefs. Add the files to be added to the directories '5' and/or '6'. Run 'adduserfiles.sh'.

A new files named 'zsos-0.10-02feb2016-extended.img' will be created. Write this image to a CF card.

Where to get additional CP/M Software

There is a huge archive of CP/M software at http://www.classiccmp.org/cpmarchives/

Forward Steps

Planned next steps for the ZSOS distribution include:

  • Add support for additional logical CP/M drives on a single physical CF card, to expand storage beyond 8MB.
  • Include additional software based on user feedback.
  • Create a banked version with a larger available TPA.

Source Code & Development Environment

The ZSOS .zip file includes copies of all files that were modified from John M's original CP/M 3 files. For a description of the tools used to create these image files (without even having access to the Z80 SBC hardware!) see the ZSOS Development Environment page


software/firmwareos/zsos/start.txt · Last modified: 2016/03/12 02:59 by admin
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