Associative Storage with a Small Computer

Use of the zone selection technique has allowed efficient use of a small computer (PDP8) as an associative analyser. The 4096 word 12 bit store operates associatively with 128 zones of 16 channels. This total of 2048 counting channels, each of 18 bits, means that 75% of the store is directly occupied with experimental data. The input 20 bit descriptor, giving a field of 1,048,576 channels, may be compounded from one, two or more parameters provided that the bits of the full descriptor are in approximate order of significance. The most significant 16 bits form the zone descriptor which is disposed in a zone descriptor store by a quasi-hash routine which also reduces the word length to 12 bits. Each zone accepted is allocated a 16 word block in the counts store which is identified by a start address held in the adjacent location in the zone descriptor store. Individual channels are then selected by the remaining 4 least significant bits of the full descriptor. A small input buffer gives a pair resolution of 10 ¿sec, while the mean input data rate is more than 10,000 descriptors per second. Live map and isometric displays are incorporated, and both display and data collection may be confined to selected areas of the data field. Separate programs, which may be introduced without disturbing the stored data, allow printout and other facilities.