The IBM 7080 was a transistorized variable word length BCD computer in the IBM 700/7000 series commercial architecture line, introduced in August 1961, that provided an upgrade path from the vacuum tube IBM 705 computer. Assorted transistors A transistor is a semiconductor device that uses a small amount of voltage or electrical current to control a larger change in voltage or current. ... In computing and electronic systems, Binary-coded decimal (BCD) is an encoding for decimal numbers in which each digit is represented by its own binary sequence. ... The IBM 700/7000 series was a series of incompatible large scale (mainframe) computer systems made by IBM through the 1950s and early 1960s. ... August is the eighth month of the year in the Gregorian Calendar and one of seven Gregorian months with the length of 31 days. ... 1961 (MCMLXI) was a common year starting on Sunday (the link is to a full 1961 calendar). ... In electronics, a vacuum tube (U.S. and Canadian English) or (thermionic) valve (outside North America) is a device generally used to amplify, or otherwise modify, a signal by controlling the movement of electrons in an evacuated space. ...

After the introduction of the IBM 7070, in June 1960, as an upgrade path for both the IBM 650 and IBM 705 computers, IBM realized that it was so incompatible with the 705 that few users of that system wanted to upgrade to the 7070. That prompted the development of the 7080, which was fully compatible with all models of the 705 and added many improvements. IBM 7070 was a Decimal Architecture intermediate data processing system that was introduced by IBM in 1960. ... June is the sixth month of the year in the Gregorian calendar, with a length of 30 days. ... Year 1960 (MCMLX) was a leap year starting on Friday (the link is to a full 1960 calendar). ... IBM 650 front panel, showing bi-quinary indicators IBM 650 front panel, rear view The IBM 650 was one of IBM’s early computers, and the world’s first mass-produced computer. ...

IBM 705 compatibility modes

For backward compatibility with the IBM 705 the machine had two switches on the operator's control panel, 705 I-II and 40K memory, that selected the mode the machine started in. In technology (especially computing), backward compatibility has several related but differing meanings: A system is backward compatible if it is compatible with earlier versions of itself, or sometimes other earlier systems, particularly systems it intends to supplant. ...

• 705 I mode — 20,000 characters (705 I-II On, 40K memory Off)
  • Indirect addressing is disabled
  • Communication channels are disabled
• 705 II mode — 40,000 characters (705 I-II On, 40K memory On)
  • Indirect addressing is disabled
  • Communication channels are disabled
• 705 III mode — 40,000 characters (705 I-II Off, 40K memory On)
  • Indirect addressing is enabled
  • Communication channels are enabled
• 705 III mode — 80,000 characters (705 I-II Off, 40K memory Off)
  • Indirect addressing is enabled
  • Communication channels are enabled

Software can then command the 7080 to enter full 7080 mode from any 705 startup mode.

• 7080 mode — 160,000 characters
  • Indirect addressing is disabled
  • Communication channels are enabled

Regardless of mode, the 7080 operates at full 7080 speed.

External link

• IBM 7080 documents on Bitsavers.org