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L > LITTON - MONROE > OC-8880   

Litton - Monroe

Info needed about this obscure CP/M computer!

Monroe - a subsidary of Litton Inc. - used to produce and sell calculators for years from 1912.

Very little is known about this CP/M system. To use the floppies you had to type in OPEN FPY0:


Thanks to Jan Söderberg for the pictures.

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Hi again all. The teledisk images have 16 sectors per track this makes them 360K. This makes them DD (Double Density) which is why I could write them on a PC with a 1.2MB drive.
The Micropolis 1015-5 in The OC-8880 is a QD 400K it seems to spin at 300 RPM but should have 20 sectors per track and 80 tracks. I thought 5,25" QD would rotate at 360 RPM similar to 8" so clock would be double of DD. I don''t know if it has two speeds and actually boots at DD and 300 RPM but can also do 360 RPM and QD.
I wonder if QD would be similar to HD and use a significantly higher current to write (bias) like PC 1.2MB does.
I will proceed to look at the floppies on another computer to see if there is anything sensible there. Also check frequencies on FDC and CPU to see if that makes sense.
The drive seems OK, though rotating speed may be a little off, if other things are OK I will try to adjust that.

Saturday 6th June 2020
Knut Roll-Lund (Norway)

I tried the TeleDisk images Alejandro Daniel Perez found. Unfortunately no success yet.

I created real media with ms-dos on a 1.2MB 5.25" drive (has 80 track) and used DD 360K media, though it is not certified for 80 track. This seemed to go well, so far so good.

The OC-8880 did respond with some more messages so it was trying. Loading, but didn''t like the floppy. From the sounds the drive may be bad.

I will try to find out if the floppies are ok on a different old computer. I will try to find out if the drive is bad, if it is an 80 track drive etc. In 1981/1982 80 track wasn''t that common. Two years later it was pretty common.

BTW I will try mesuring what frequency the CPU has, and confirm if signals match Z80.

Thursday 28th May 2020
Knut Roll-Lund (Norway)

Hi everyone! I believe that I have found a disk image to check with this computer here:

The image name is monroe.td0 and monroe88.tdo, if anyone can check it I would like to know if the images are working fine. I have a Monroe OC-8820 but it still under repair

Thursday 16th April 2020
Alejandro Daniel Perez (Argentina)


NAME  OC-8880
MANUFACTURER  Litton - Monroe
TYPE  Professional Computer
YEAR  1981
KEYBOARD  Full stroke keyboard with function keys and numeric keypad. 93 keys.
CPU  Z80
SPEED  Unknown
RAM  16 KB (128 KB max)
ROM  Unknown
COLORS  Unknown
SOUND  Unknown
SIZE / WEIGHT  Unknown
I/O PORTS  External disk drive, expansion bus, composite video output (monochrome), AUX serial I/O, COMM I/O, parallel printer interface
BUILT IN MEDIA  One 5.25'' disk drive (300 KB)
PRICE  Unknown

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