IBM 7080

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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.

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.

[edit] 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.

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