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Core Memory for PDP-8/I, PDP-8/L and PDP-12


Core Memory Assembly for PDP-8/I and PDP-8/L S M L XL

The boards were damaged, and some of the inter-board wiring was damaged as well, making repair (by mere humans) just about impossible. That's why I chose to disassemble this particular core memory.

Core Memory Assembly for PDP-8/I and PDP-8/L S M L XL

This is the complete (disassembled) core memory "stack". There are 3 boards of core memory, two diode boards (with 256 diodes each), and two paddle boards for additional connections.

Core Memory for PDP-8/I and PDP-8/L S M L XL

This is what the main core planes for the PDP-8/I, PDP-8/L, and PDP-12 look like. Here you can see 4 planes of 64x64 (4096) bits.

In total, the 3 core memory boards give a total of 12 planes of 4096 bits (4096 x 12 is the core memory size, so 49,152 individual cores).

Back of Core Memory for PDP-8/I and PDP-8/L S M L XL

This is the reverse side of the core board, showing how the 4 planes are interconnected.

PDP-8/I and PDP-8/L core memory lattice S M L XL

This is the main lattice of the core plane.

PDP-8/I and PDP-8/L core memory edge of lattice S M L XL

This is at the edge of the lattice, and gives a good view of the winding of the sense/inhibit wires.

PDP-8/I and PDP-8/L core memory wiring join S M L XL

The little blob in the center of the picture shows where wires were joined. (Pity about all the dirt on the core! -- to the naked eye, the core looked fairly clean.)

PDP-8/I and PDP-8/L extreme closeup S M L XL

And finally, an extreme closeup of the core.


A note about the last four (microscope) slides.

Relatively speaking, the subject matter is extremely deep compared to most flat objects that are typically placed under a microscope. This means that the pictures you see above are not exactly what you'd see if you looked through the microscope; they are a composite of many pictures. Basically, the topmost feature of the core was brought into focus and photographed. Then, the focus was changed downwards slightly, and another picture was taken. This continued (an average of 20 shots for the first three, and 94 shots for the high resolution bottom pictures) until the bottom of the feature was in focus. Then, software was used to extract only the "in focus" parts of the image, resulting in the composites you see above.

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