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
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.