How powerful was the Apollo 11 computer?

When the IBM PC “XT” was released in 1981, the lowest end configuration had 8 times more memory than Apollo’s Guidance Computer — 16k, vs the Apollo’s 2k. The read-only storage of the AGC was 32k,

The IBM PC XT also ran at a dizzying clock speed of 4.077MHz. That’s 0.004077 GHz. The Apollo’s Guidance Computer was a snail-like 1.024 MHz in comparison, and it’s external signaling was half that — actually measured in Hz (1/1000th of 1 MHz, much as 1 MHz is 1/1000 of 1 GHz).

Internally, the 8086 had 8 16-bit registers available to work with — for those not familiar with the internals of a processor, a register is much like the numbers you’d keep in your head while doing math, and “memory” is more like scratch paper where you write things down for later use. The 8086 could keep track of 8 of those, the Apollo Guidance Computer held just 4. (The AGC also had a host of other non-general purpose registers, ranging from 1 to 16 bits in width, but it’s difficult to compare those with the architecture of the 8086)

Regardless, we’ve established that we’re dealing with some pretty archaic hardware. In many ways, the AGC was half the IBM PC XT you could buy off the shelf just a decade or so later. What’s so incredible about that? The part that blew me away when reading up on the Apollo Guidance Computer wasn’t so much the hardware, as the software they wrote to exploit it.


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