The computer technology didn't exist in the 1960s to make the Apollo guidance computer.

This goes along with the general discussion about the state of technology available to NASA in the 1960s, but since I have special expertise in computer technology, I'll treat it separately.

As with the general level of technology, conspracists often try to compare the availability and sophistication of consumer computing equipment with that available to NASA. Computer companies of the 1950s and 1960s had to produce general purpose computers at a cost that would attract business and scientific customers. NASA had to solve only one problem -- guidance -- and could easily afford to have a custom system designed and built for them using cutting edge components and techniques.

We could today, if we wanted, produce very fuel-efficient automobiles that would go for hundreds of thousands of miles without any regular service or mechanical breakdown. Unfortunately that car would cost well over a million dollars a unit, and would therefore be out of reach of most consumers. And so automobile companies produce vehicles more tailored to the economy of their intended customer. As a result the level of technology lags behind what would be achievable if money was no object.

The question to ask is not what kinds of computers were available in IBM's color brochures, but what kind of computer was available to NASA with its bottomless pockets.

The Apollo guidance computer had the computer power equivalent only to today's kitchen appliances, far less than what would be required to go to the moon.

It always amuses me to hear this from people who sit at gigahertz computers and can't imagine that anything less was ever remotely usable for anything.

This is a good example of a mental technology trap. People believe that because we use a particular technology to solve a particular problem today, that problem wasn't solvable before the technology was available.

As a matter of fact, John Glenn flew his spacecraft to earth orbit without any onboard computer whatsoever. Yet the trajectory was precisely controlled, and his capsule could have operated completely automatically if necessary. (In fact, the original design called for it to be completely automated, but the astronauts demanded the ability to pilot the capsule.)

Computer chips weren't invented in 1969, so there's no way NASA could have built the Apollo computers.

It all depends on what you mean by "computer chips". Today a modestly priced Intel Pentium series microprocessor has registers, memory cache, floating-point processor, and graphics accleration built right into the chip. Not so long ago those added functions had to be provided by additional chips. Putting a complete CPU on a single chip was indeed a breakthrough, but microchips performing simple tasks were available in the early 1960s and these could be built up into processors.

Electronics hobby stores carry project kits that use simple integrated circuits. With patience, even these very simple chips (e.g., a quad NAND gate) can be combined to make a simple computer. In fact this is often an assignment for advanced digital design classes in college. These simple chips are not "computer chips" in the sense that they contain a computer on a single chip, but they are computer chips in that they can be used to build a computer.

Fairchild Camera and Instrument Corporation released a commercially available integrated circuit, an SR flip-flip, in 1961. The rest of the RTL integrated circuit product line appeared later that year. By 1963 Fairchild had doubled the density of its chips. Philco produced the Apollo ICs to the same density and had perfected them by 1966.[Hall96]

RCA introduced the Spectrum 70 computer in 1965 using Fairchild-type integrated circuits. IBM introduced the System/360 that same year using miniscule diodes and transistors potted on microscopic circuit boards -- its own version of integrated circuits. The System/360 was the workhorse of the commercial computing industry for more than a decade.

Computers in the 1960s were huge, heavy machines that took up entire rooms in air-conditioned buildings.

Some were and some weren't. Recall that the Apollo computer was not a general purpose computer. It didn't have to run games or spreadsheets, or do payrolls, or store inventory databases. It only had to navigate the spacecraft to the moon. There were no printers or disk drives required. No tape drives, no card readers or card punches. And so it was a pretty lean computer.

Calling the Apollo guidance system a computer is probably a bit of an exaggeration. It's more closely related to what we call a microcontroller today, or perhaps a digital autopilot. Most of the number-crunching was done on at Mission Control on several mainframe computers. The results were transmitted to the Apollo guidance computer which acted on them. The onboard computer could only compute a small number of navigational problems itself.

There is a big difference between computers intended for general use and digital guidance systems such as those built for aerospace. General purpose computers have to be reasonably priced so that enough of them can be sold to make it worthwhile as a product. This means they can be bulkier and consume more electricity if that makes them cheaper to produce. Aerospace computers need to be light and small, even if that makes them very expensive to produce.

The maker of a general purpose computer doesn't know or care what the customer will use it for. This requires him to provide the computer with mostly RAM memory that can store whatever program the customer chooses to run. And since many, like the IBM System/360, were designed as time-sharing systems, they had to have the capacity to change programs very easily and rapidly. But guidance systems only have to run one program, so it's best to put that program in some kind of ROM and provide only enough RAM to hold the temporary results of guidance calculations.