Osborne Model 1

ROMs

• [2732] Original Osborne BIOS vers. 1.40 (from my Osborne)
• [2732] Original Osborne BIOS vers. 1.43
• [2732] Original Osborne BIOS vers. 1.44 (latest)
• [2732] 3rd party Micro Management OZROM 1E (thanks to user nelgin on VCFED Forums)
• OZROM manual (cleaned up version thanks to VCFED user booboo)
• [2764] Combined OCC v1.44 & OZROM (requires daughterboard below)
• [2716] Original Osborne character generator ROM (from my Osborne)
• [2716] Original Osborne Screen Pac BIOS Rev. A

Differences between ROM v1.4 and v1.44 include:

; CBOOT - added seek 10 tracks and home drive
; GKEY - fixed bell bug
; SENDEN - changed the number of retrys to NRETRY
; PSEKC - added disk head settle delay
; SELDRV - changed start up delay to 500 ms

OCC v1.4 ROM

OCC Character Generator ROM

Micro Management OZROM

Daughterboard

[29-Aug-2024: tested successfully]
ROM daughterboard to accomodate 28-pin 2764 (8KByte) EPROM in the Osborne's 24-pin 2732 (4KByte) BIOS socket. Idea is to allow switching between the official Osborne ROM and the 3rd party OZROM.

Address pin A12 is pulled high by the 10KΩ resistor (so default is upper ROM address range 0x1000 to 0x1FFF) or can be switched to ground via a strapping or switch connected to the A12 pin header (so lower ROM address range 0x0000 to 0x0FFF).

Using A Gotek

Big thanks to Dave Dunfield for the original ImageDisk-format (IMD) disk images.

How to tell if an Osborne 1 disk image is single density (SD) or double density (DD)?

Both disk formats have 40 tracks:

• SD disks have ten 256 byte sectors per track (2560 bytes/track) -> 92KByte formatted capacity
• DD disks have five 1024 byte sectors per track (5120 bytes/track) -> 184KByte formatted capacity

Example output of fsed.cpm info command on an IMG disk image:

              Sector length: 1024
           Number of tracks: 40
          Sectors per track: 5

EXMON Video Output

Photos of the EXMON video output shunt.

• Sullins MP-0100-10-DS-4 card edge connector
• Hyko K688-DI - this appears to combine horizontal & vertical sync with the video output, powered by +12V

Double Density Upgrade

Photos of the original Osborne DD upgrade board and details of a modern reproduction board.

Screen Pac Upgrade

Photos of the Screen Pac board.