What kind of error did a 404 code signify within the operating system of the Apollo Guidance Computer, the first embedded system ever put to practical use, and the computer that accompanied the first human beings to land on the moon?
One of the prevailing criticisms of the U.S. space shuttle program is that it is comprised of antiquated equipment. Designed in the 1970s, built in the 1980s, and with two decades of operational fatigue on the fleet, Discovery, Endeavor, and Atlantis aren't cutting edge technology in any respect — especially their computer systems. The space program is an exercise in proven, cost-effective, work-horse tech, rather than the latest and greatest innovations.
We've come a long way since the days of Apollo.
When Apollo 11 set forth for the moon in 1969, it carried with it what were then arguably the two most advanced computers ever built. The Apollo Guidance Computer — two of which went on every manned moon mission — was the first computer to use integrated circuitry and was thus the first modern embedded computer system ever put to use. Custom-designed by MIT and purpose-built by Raytheon, the Apollo Guidance Computer was the basis for the world's first fly-by-wire systems, which in turn directly influenced the design of the space shuttle's flight control systems.
Not bad for a 2 MHz, 16-bit system with a four kilobit RAM allotment and 32K of fixed memory. (And that was the Block II advanced model; earlier Apollo shakedown missions used an even more limited Block I design.) The Apollo Guidance Computer had a 19-key calculator-style keyboard that astronauts used to program the system with two-digit commands. Bear in mind, the first commercially available pocket calculator wasn't sold until 1967, when Texas Instruments debuted a basic function model (add, subtract, multiply, and divide) for about $100. A calculator-esque interface was cutting edge for 1969.
That isn't to say the Apollo Guidance Computer — advanced as it was for its era — was error free. The AGC that ran the Apollo 11 lunar module's Primary Navigation, Guidance, and Control System (PNGCS, pronounced pings) malfunctioned during the first lunar descent. Fortunately, the error codes 1201 and 1202 didn't faze Buzz Aldrin and Neil Armstrong when they popped up, informing the astronauts of a critical buffer overflow. (Two radar systems were feeding the Apollo Guidance Computer data simultaneously due to an error in flight protocol.) The Apollo Guidance Computer simply popped into a failover mode and — because the system was designed with 15 percent spare memory capacity in case of error — the mission went off without a hitch. If the Apollo Guidance Computer had thrown a 404 error, it might have been a different story.
WHAT DID A 404 ERROR CODE SIGNIFY IN THE APOLLO GUIDANCE COMPUTER SOFTWARE SYSTEM?Get the answer.