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The 3B1 (also known as the PC7300, or Unix PC) was a Unix workstation computer originally developed by Convergent Technologies (later acquired by Unisys), and marketed by AT&T in the mid- to late-1980s. Despite the name, the 3B1 had little in common with AT&T's other 3B-series computers.

3B1 / PC7300 / Unix PC
Atandt unix pc.jpg
AT&T Unix PC
ManufacturerConvergent Technologies
TypeProfessional Computer
Release date1985 (1985)
Media5¼-inch floppy disks, optional quarter-inch cartridge tapes
Operating systemAT&T Unix v3.51
CPUMotorola MC68010 with custom Memory management unit clocked at 10Mhz
Memory512KB to 4MB RAM
StorageOptional 10MB, 20MB, 40MB, and 67MB hard drives
Display720x348 pixel resolution
InputKeyboard, 3-button Mouse


Hardware configurationEdit

Exterior of the AT&T 3B1
  • 10 MHz Motorola MC68010 (16 bit external bus, 32 bit internal) with custom, discrete MMU
  • Internal MFM hard drive, originally 5 MB, later models with up to 67 MB
  • At least 512K RAM on main board, expandable via expansion cards
  • 3 expansion slots
  • Monochrome green phosphor 10-inch (250 mm) monitor
  • Internal 300/1200 bit/s modem


The initial PC7300 model offered a modest 512 KiB of memory and a small, low performance 5 MB hard drive. This model, although progressive in offering a Unix system for desktop office operation, was underpowered and produced considerable fan and drive bearing noise even when idling. The modern-looking "wedge" design was innovative, and in fact the machine gained notoriety appearing in many movies as the token "computer."[citation needed]

AT&T 3B1Edit

A later enhanced model was renamed "3B1". The cover was redesigned to accommodate a full-height 67 MB hard drive. This cover change added a 'hump' to the case, expanded onboard memory to 1 or 2 MB, as well as added a better power supply.

Operating systemEdit

Video of an AT&T PC7300 booting
AT&T PC7300 compiling and running a C program

The operating system is based on Unix System V Release 2, with extensions from 4.1 and 4.2 BSD, System V Release 3 and Convergent Technologies. The last release was 3.51.

Programming languagesEdit

Application softwareEdit

Word processorsEdit



The StoreEdit

The Store is a public domain software repository which was available for all 3B1 users.[4]

Expansion CardsEdit

  • DOS-73 8086 co-processor card running MS-DOS, which could be fitted with an 8087 math co-processor chip. This board was designed and built for AT&T by Alloy Computer Products of Framingham MA.
  • RAM card could be added using 1 or 2 MB RAM cards (up to a maximum of 4 MB)
  • EIA/RAM combo cards contained extra RAM and two RS-232 serial ports.
  • Dual EIA port card
  • StarLAN 1Mbit/s LAN card
  • Ethernet 10 Mbit/s LAN card
  • VoicePower card allowed for the capture and digital recording of voice conversations.
  • Tape drive card provided interface for 23 MB MFM Tape Cartridge Drive.
  • Expansion chassis card was hard-wired to Expansion Chassis (with five added slots)


See alsoEdit

External linksEdit