Von Neumann: The Computer: Characteristics of Modern Digital Machines (The Computer and the Brain, 1958)

computerbrainComprises “active” and “memory” organs (he’s including “input” and “output” as part of “memory).

Active organs: perform basic logical actions, sense coincidences and anticoincidences, and combine stimuli, regenerate pulses to maintain pulse shapes and timing via amplification of the signals.

These functions were performed by (in historical succession): relays, tubes, crystal diodes, ferromagnetic cores, transistors, or by combinations of those.

A modern machine will contain 3,000-30,000 active organs, of which 300-2,000 are dedicated to arithmetic, and 200-2,000 to memory. Memory organs require further organs to service and administer them—the memory parts of the machine being around 50% of the whole machine.

Memory organs are classed by their “access time”—the time to store a number, removing the number previously stored, and the time to ‘repeat’ the number upon ‘questioning’ (that is, write/read times, respectively). To classify the speed, you could either take the larger of those two times, or the average of them. If the access time doesn’t depend on the memory address, it is called “random access” (RAM).

Memory registers can be built of active organs—which, while fastest, are also most expensive (i.e,. built out of vacuum tubes). Thus, for large-memory operations, it’s cost-prohibitive. Previously, relays were used as the active organs, and relay registers were used as the main form of memory.

It is possible, however, to reduce the required memory to solve a problem by considering not the total numbers needed in memory, but the minimum needed in memory at any given time. And if that can be determined, numbers can be distributed between faster memory, and slower memory, based on when they are needed—that is, perhaps all the numbers can be stored on the slower memory, while the necessary numbers of the moment are stored on the faster memory. I assume this is how computers now function—everything is stored on the hard drive, while the absolutely necessary things to the current operations are stored in the RAM.

Magnetic drums and tapes are currently (1950s) in use, while magnetic discs are being explored (and now, 2015, becoming obsolete in favor of SSDs).

Inputs are punched cards or paper tapes, outputs are printed or punched paper—that is, means for the machine to communicate with the outside world.

Words are saved directly to named numerical addresses within the memory of the machine—the address is never ambiguous.


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