Ferrite Core Memory Plate manufactured in the USSR in 1974
Plate size (approx):14 x 14 cm (5.5 x 5.5 inch in US unit of
ferrite toroid = 1 bit
A 64 x 64 core memory plate stores 4096 bits of data
CONDITION: excellentcondition without broken wires
plate is one of 14 plates forming a ferrite core memory block that has been removed from the control computer -- Soviet minicomputer, clone of DEC
PDP-8/M but more bulky
capacity of the whole block is 57344 bits or 4096 twelve-bit words (4 Kwords). Ferrite cube is
shown on 11 (opened) -12 (unopened) pictures. There were 8 ferrite core memory cubes in minicomputer. Total memory was
Legend reads as clone was made from minicomputer PDP-8/M that has been
acquired from US
made in Central Research Institute of measuring equipment (ЦНИИИА), the city ofSaratov
Offered storage core plate is an example of magnetic-core storage — devices consisting of an array of magnetic cores.
Up to the beginning of 1970th in the USSR ferrite core memory plates have been woven manually. That painstaking work requiring much rapt attention and perseverance was entrusted to young women with sharp eyesight.
Magnetic-core memory was the predominant form of random-access computer memory for 20 years (circa 1955-75).
Magnetic core — a tiny ferrite toroid of a hard magnetic material that can be magnetized in either of two directions formerly used in a random access memory to store one bit of data; now superseded by semiconductor memories.
The most common form of core memory, X/Y line coincident-current – used for the main memory of a computer, consists of a large number of small ferrite (ferromagnetic ceramic) toroids — cores— held together in a grid structure (each grid called a plane), with wires woven through the holes in the cores' middle. On a given plane there are four wires, X, Y, Sense and Inhibit. Each toroid stores one bit (a 0 or 1). One bit in each plane could be accessed in one cycle, so each machine word in an array of words was spread over a stack of planes. Each plane would manipulate one bit of a word in parallel, allowing the full word to be read or written in one cycle.
To read a bit of core memory, the circuitry tries to flip the bit to whatever polarity the machine regards as the 0 state, by driving the selected X and Y lines that intersect at that core.
If the bit was already 0, the physical state of the core is unaffected.
If the bit was previously 1, then the core changes magnetic polarity. This change, after a delay, induces a voltage pulse into the Sense line.
Detecting such a pulse means that the bit contained 1. Absence of the pulse means that the bit contained 0.
Following any such read, the bit contains 0. This illustrates why core memory features destructive reads: Any operation that reads the contents of a core erases those contents.
To write a bit of core memory, the circuitry assumes there has been a read operation and the bit is in the 0 state.
To write a 1 bit, the selected X and Y lines are driven, with current in the opposite direction as for the read operation. As with the read, the core at the intersection of the X and Y lines changes magnetic polarity.
To write a 0 bit (in other words, to inhibit the writing of a 1 bit), the same amount of current is also sent through the Inhibit line. This reduces the net current flowing through the respective core to half the select current, inhibiting change of polarity.
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