For a bit of mid-week cheer, let me share a *fantastic* techno-archaeologist photo essay Ken did on my core memory module from the LVDC (Launch Vehicle Digital Computer). It holds the flight program for Apollo, guiding the huge Saturn V rocket from launch to low-Earth orbit to trans-lunar injection. This triple-redundant autopilot system saved the Apollo 12 mission when lighting struck the rocket twice early in the launch, knocking out displays and controls for the astronauts.
I love the wrap-around electronics design — not yet a fully planar mindset. The outer wrap consists of timing, drive, inhibit and sensing circuits for the magnetic memory array. Built by IBM for NASA, it is festooned hybrid ceramic modules, not integrated circuits. At this point in 1966, the Apollo program consumed 60% of global semiconductor output. (It was also the year that my dad entered the semiconductor manufacturing business, immigrating to Arizona for a job at Motorola, and that is I why I am a U.S. citizen.)
This module stores 106k bits (4096 words of 26 bits + 2 parity bits, across 14 planes) in a five-pound block. More interesting still is the ghost in the machine. The little iron rings within still hold whatever program they had when powered down (the magnetic memory does not fade). Since there are no tapes or archives of the code saved anywhere by NASA, it is possible that the only remaining copy of the Saturn V flight program is in cores like this.
Ken opens with “This memory module was technologically advanced for the mid-1960s, using surface-mount components, hybrid modules, and flexible connectors that made it an order of magnitude smaller and lighter than mainframe core memories (of the day). Even so, this memory stored just 4096 words of 26 bits.”
On the inside, a stack of woven iron core planes like this one:
"This plane has 128 X wires running vertically and 64 Y wires running horizontally, with a core at each intersection. For reading, a single sense wire runs through all the cores parallel to the Y wires. For writing, a single inhibit wire (explained below) runs through all the cores parallel to the X wires. The sense wires cross over in the middle of the plane; this reduces induced noise because noise from one half of the plane cancels out noise from the other half."
"the inhibit board is on the underside of the core module and holds the inhibit drivers that are used for writing to memory. There are 14 inhibit lines, one for each plane in the core stack. To write a 0 bit, the corresponding inhibit driver is activated and the current through the inhibit line prevents the core from flipping to a 1. Each line is driven by an ID-1 and ID-2 (Inhibit Driver) module and a pair of transistors. The high-precision 20.8Ω resistors at the top and bottom of the board regulate the inhibit current. The 14-wire flex cable on the right connects the drivers to the 14 inhibit wires in the core stack."
"The photo below shows the internal components of a ULD module. On the left, the circuit traces are visible on the ceramic wafer, connected to four tiny square silicon dies. While this looks like a printed circuit board, keep in mind that it is much smaller than a fingernail. On the right, the black rectangles are thick-film resistors printed onto the underside of the wafer."
Circuit diagram as an INV module, as an example:
"Closeup of X diode matrix showing diodes mounted vertically using cordwood construction between two printed circuit boards. The two X driver boards are above the diode board, separated from it by foam. Note how the circuit boards are packed very closely together."
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