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Core Stack

Technical Information

Catalogue No: C1059
Category: Unknown
Object Type: Module/Sub-Assembly/Component
Object Name: Core Stack
Part No: P259 Issue 8
Serial No: 44-082
Manufacturer: GEC Computers
Division: Unknown
Year of Manufacture: Unknown
Width (mm):
Height (mm):
Depth (mm):
Weight (g):
Location: Main Object Store

Manufactured by
GEC-Comupters Limited
Core Stack
322 Purch 259
Serial No:- 44-082
P259 Issue 8
IGV 044254
Made in UK
Plessey Core Store
Type No. 73'1556'A
Serial No. 44082
Ref. No. P259 Issue 8
Towcester England


This is a low-density early stacked 8k x 18-bit core memory array, made by Plessey Components Ltd, Towcester, England. Plessey made core memories for a number of computer companies, and for example made 48-bit core memories for the Ferranti Atlas and for the English Electric KDF9. This type of stack was also used in the Elliott 903,and 920B computers in the mid 60’s.
Magnetic-core memory was the predominant form of random-access computer memory for 20 years between about 1955 and 1975. Such memory is often just called core memory, or, informally, core.
Core uses tiny magnetic toroids (rings), the cores, through which wires are threaded to write and read information. Each core represents one bit of information. The cores can be magnetized in two different ways (clockwise or counterclockwise) and the bit stored in a core is zero or one depending on that core's magnetization direction. The wires are arranged to allow for an individual core to be set to either a one or a zero and for its magnetization to be changed by sending appropriate electric current pulses through selected wires. The process of reading the core causes the core to be reset to a zero, thus erasing it. This is called destructive readout. When not being read or written, the cores maintain the last value they had, even when power is turned off. This makes them nonvolatile.

The cores in the stack However the robust construction of the unit and its colour suggests a military application, and probably from the Integrated Fire Control System (IFCS) for the Challenger Mk1Tank. The Challenger Mk1 went into service in 1983 but development of the Fire Control System was underway in the previous decade. The system activity was at Marconi Space and Defence Systems on the but the 12/12 computer and Power Supply were produced at Rochester. The gunnery control system was accurate but slow and it was replaced in the Challenger Mk2.

The stack is marked on the top:
TOWCESTER, PLESSEY COMPONENTS, ENGLAND with the Plessey ‘Oscilloscope’ mark. Another label on the top has:
Yet another label also on the top has:
Manufactured by GEC Computers Limited, CORE STACK 322 PURCH 259,
Serial No. 44082, P259 Issue B. Borehamwood England. A subsidiary of the General Electric Company.

The Core Stack dates from about 1973 and many items at that time in the 903 Computers were marked with"322 PURCH" numbers, (most transistors are 322 PURCH 100 and diodes were 101).

322 might be the divisional number of Mobile Computing, and Airborne Computing Division (ACD) had the Divisional number 363 in Borehamwood then 263 in Rochester.

The length of the two Flexi-PC interconnections are 105mm.
The length of the two wired interconnections are 125mm.

Click to enlarge Click to enlarge
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