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744 Part 3 ½ Computer Classes Section 4 ½ Maxicomputers

The printed circuit board used in the CRAY-1 is a 5-layer board with the two outer surfaces used for signal runs and the three inner layers for - 5.2V, - 2.0V, and ground power supplies. The boards are six inches wide, 8 inches long, and fit into the chassis, as shown in Fig. 3.

All integrated circuit devices used in the CRAY-1 are packed in 16-pin hermetically sealed flat packs supplied by both Fairchild and Motorola. This type of package was chosen for its reliability and compactness. Compactness is of special importance; as many as 288 packages may be added to a board to fabricate a module (there are 113 module types), and as many as 72 modules may be inserted into a 28-inch-high chassis. Such component densities evitably lead to a mammoth cooling problem (to be described).

Main Memory Speed

CRAY-1 memory is organized in 16 banks, 72 modules per bank. Each module contributes 1 bit to a 64-bit word. The other 8 bits

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