Osborne 1


  • Type: Portable computer
  • Manufacturer: Osborne Computer Corp.
  • Released: 1981
  • OS: CP/M 2.2
  • CPU:  Z80 @ 4 MHz
  • Memory: 64 KB RAM
  • Sound: 1 bit beeper
  • Video: 52 character x 24 line text mode
  • Monitor: 5″ monochrome CRT (external 12″ monitor available)
  • Ports: RS-232 compatible serial port, parallel port configurable as an IEEE-488 port
  • Storage: 2 x 5.25″ single-sided, single-density (dual-density upgrade available)
  • Weight: 10.7 kg (24.5 lb)
  • Dimensions: W:51 cm x D:32,5 cm x H:22,5 cm
  • Successor: Osborne Executive

Released 1981: The Osborne 1 is an early portable microcomputer, released on April 3, 1981 by Osborne Computer Corporation. However it’s not the very first portable computer, for example the IBM 5100 Portable Computer was introduced in September 1975, and predates it with almost six years.

It weighs 10.7 kg (24.5 lb), costed US$1,795 at introduction, and runs the CP/M 2.2 operating system. It’s powered from a wall socket as it has no internal battery. However, an external battery was later available and gave it an operational time for around one hour.

The computer shipped with a large bundle of software that was close in value to the machine itself, a practice adopted by other CP/M computer vendors. Competitors quickly appeared, such as the Kaypro II.

The Osborne 1 was developed by Adam Osborne and designed by Lee Felsenstein, first announced in early 1981. Osborne, an author of computer books decided that he wanted to break the price of computers. The computer’s design was based largely on the Xerox NoteTaker, a prototype developed at Xerox PARC in 1976 by Alan Kay. It was designed to be portable, with a rugged ABS plastic case and a handle. The Osborne 1 is about the size and weight of a sewing machine and was advertised as the only computer that would fit underneath an airline seat. It is now classified as a “luggable” computer.

Osborne 1 in my collection
Osborne 1 with boot screen, as seen in my collection

The Osborne 1 was described as “a cross between a World War II field radio and a shrunken instrument panel of a DC-3”, and Felstenstein admitted that carrying two of them to a trade show “nearly pulled my arms out of their sockets”. The computer nonetheless amazed observers; InfoWorld reported that “By far the most frequently asked question at” the West Coast Computer Faire “was, ‘What do you think of the new Osborne computer?'” BYTE Magazine wrote: “it will cost $1795, and it’s portable!” The word processing, spreadsheet, and other bundled software alone was worth $1,500; as InfoWorld stated in an April 1981 front-page article on the new computer after listing the included software, “In case you think the price printed above was a mistake, we’ll repeat it: $1795”.

West Coast Computer Faire attendees stated, InfoWorld said, that the Osborne 1 “represented an advancement of the price/performance ratio for microcomputers”. Adam Osborne agreed but emphasized the price, stating that its performance was “merely adequate”: “It is not the fastest microcomputer, it doesn’t have huge amounts of disk storage space, and it is not especially expandable.” Beyond the price, advertisements emphasized the computer’s portability and bundled software. The company sold 11,000 units in the first eight months of sales, and sales at their peak reached 10,000 units per month.

The Osborne 1’s principal deficiencies are a tiny 5 inch display screen, use of single-sided, single-density floppy disk drives which store 90KB per disk, and considerable unit weight. Adam Osborne decided to use single-sided disk drives out of concern about double-sided drives suffering head damage from rough handling. A single-density disk controller was used to keep costs down.

In September 1981, Osborne Computer Company had its first $1 million sales month. Sales were hurt by the company’s premature announcement of superior successor machines which replaced the Osborne 1’s 40 character screens with an 80 character screen such as the Osborne Executive, a phenomenon later called the Osborne effect. From 1982 to 1985, the company published “The Portable Companion”, a magazine for Osborne users.

My Osborne 1

These machines got a RIFA filter capacitor on the AC inlet that is notorious for exploding when you turn the computer on. Luckily the previous owner had already replace the filter capacitor as he is a retro computer enthusiast himself. After I got the machine, the previous owner also found all of the original manuals, import papers, receipt, license for CP/M and the diskettes that came with the machine when it was new. He was kind to send me all this in a separate package.

Screen-Pac: It came with an internal “graphic card” upgrade that let you switch between original 52 column, 80 column and 104 column modes. It have an RCA jack installed on the front panel to allow users to connect to an external composite monitor. I didn’t got any display on an external monitor at first, but this turned out to be caused by the cable from the Screen-Pac card to the RCA jack had loosened inside the machine, an easy fix.

Double Density floppy drives: Turned out, my machine was sold new with DD 180 KB drives installed instead of the usual 90 KB SD drives. Also the bundled software disks that came originally with my unit was in DD format. This makes it easy to write out disks from image files using a regular PC computer with a 5.25″ floppy drive. Usually PC’s struggles with writing single density 90 KB disks.

Osborne 1

Remi Jakobsen

I'm collecting classic computers and video games, stretching from the 70's into the 90's. Restoration, history, usage ...

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2 thoughts on “Osborne 1

  1. Hi we’re going through my father’s things. His Osborne computer and the dotmatrix printer as well as the owners guide and the start pack have been found in the garage. And we were wondering what to do with it and if you might be interested.

    1. Thanks for letting me know, I’m interested.

      Garage might not be the best place for storage over the years do to temperature climate.

      How does it look condition wize? Where do you live? How much do you want?

      Maybe you could send me an email at remi@remimedia.com ?

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