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I > IBM  > AN/FSQ-7   


The AN/FSQ-7 was by far the largest computer ever built, and is expected to hold that record. It consisted of two complete Whirlwind II computers installed in a 4-story building (See the impressive diagram in the 'More Pictures' section).

Each AN/FSQ supported more than 100 users. IBM had about 60 employees at each site for round-the-clock maintenance.
Keeping one unit operating and one on hot standby (to allow for switchover when vacuum tubes failed) resulted in better than 99% uptime. The roles of the two units were reversed at regular intervals, allowing diagnostics and maintenance to be carried out on the standby unit.

There were usually several hundred tube failures each day, replaced by workers racing up and down the tube racks with shopping carts full of replacements. Automated tests run by the computer itself would cycle the voltage to the tube racks down and back up to induce marginal tubes to fail early, so that the computer would normally run correctly for the rest of the day. Without this process, the MTBF would have been a few minutes.

By the time SAGE was deployed (22 or 23 stations in the period 1959-1963; sources disagree) it was nearly obsolete, since it was designed to detect bombers, not the new ICBMs. Nevertheless it was operational until 1979, when the ROCC (Regional Operations Control Centers) system took over, using much higher-speed computers. One SAGE station continued operating until 1983. This last unit was donated to the Boston Computing Museum, since relocated to Moffett Field in Mountain View, California. The museum also has a tube panel from the Whirlwind I. Whirlwind II consoles turned up in the TV series Battlestar Galactica.
In spite of its limited military value, the SAGE system served as an excellent prototype for an air-traffic control system. The FAA operated its own AN/FSQ-7 systems for many years after SAGE was shut down. IBM's experience with these systems had a great deal to do with its later success in computer systems, and its dominance of the market for large computers. The IBM 7090 was essentially a solid-state version of the AN/FSQ-7/8. (The 7090 has its own rich history, including hosting the first-ever multiuser APL system.)

• First CRT-based real-time user interface,
• First use of light gun to pick an item on the screen,
• First wide-area modem communications (1300 bps),
• First hot standby system for maximum uptime,
• First ground control of interceptor aircraft,
• The first in line microfilm fast processed 35 mm projection displays, preceding printer/plotters. A screen capture could be displayed within 30 seconds, • First two-pass assembler, permitting symbolic addresses.

Thanks to Edward Cherlin, Simputer Evangelist, for all this information.

The photo (from Mitre) shows the rear panel wiring of FSQ-7 arithmetic element frame.

We need more info about this computer ! If you designed, used, or have more info about this system, please send us pictures or anything you might find useful.
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I joined IBM in Kingston in 1959 and after 20 weeks of training I was assigned to the Duluth ADS SAGE location as a Central Computer Field Engineer. I was there for five years. I never saw anyone racing the aisles with replacement pluggable units (PUs). Nor did I witness large numbers of tubes failing daily. Most of the tubes were in the pluggable units which were repaired in the PU lab. A great time.

Sunday 12th June 2022
Richard Wayne (United States)

Unfortunately my own father''s experiences directly contradict Glen Crandall''s statement. He absolutely witnessed people running up and down the aisles of tubes, replacing them with shopping carts, while he was an operator on the AN/FSQ-7 in Michigan. My assumption is that the load they were under simply wasn''t enough to trigger that many failures, because they deliberately induced them twice a day and still managed to need people running up and down the aisles replacing them.

Wednesday 15th December 2021
Jacob Coleman (Unites States)

I programmed the AN/FSQ-7 computer to play music in 4-part harmony. I was a student in the USAF Command $ Control Computer Programming course at Keesler AFB in Mississippi in 1965.. I was a 2nd lieutenant at the time, later becoming an instructor. I have a recording of four pieces of music I programmed that was played at the Montgomery Air Defense Sector site in Mobile, Alabama in 1965. I can send you a copy of the music if you email me requesting it ( I had heard some previously written tunes that had been written with one and two parts. I speculated that if played at the proper speed, I could program an accumulator bit to repeat four notes of a chord to simulate four part harmony. I wrote a test program to do that. After I picked the proper speed, I then programmed these four pieces of music.

Monday 23rd August 2021
Henry Spencer (United States)


TYPE  Professional Computer
YEAR  1958
KEYBOARD  IBM consoles
CPU  55,000 vacuum tubes in each unit
SPEED  75 KIPS (KiloInstructions Per Second)
RAM  Core 8892-word
ROM  Unknown
GRAPHIC MODES  256 x 256
COLORS  Monochrome
SOUND  Speaker (see the ''Read more'' page)
SIZE / WEIGHT  2000 square meters / 275 tons
I/O PORTS  Tape, punched cards, modem
OS  None
PRICE  $238 million, printer around $200,000 to $250,000

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