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IBM History

Hardware Detail

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  Card Capacitor Read Only Storage
  This is the Card Capacitor ROS used in System/360 Model 30. The storage card looks like an IBM punched card except it is made of Mylar and has metal lines etched on it. Each card has 12 word lines corresponding to the 12 rows on a standard punched card. The contacts for the word lines are on the right in the picture. Each word line attaches to 60 bit "pads" (again corresponding directly to the punch positions in a standard IBM card). The metal pad can be eliminated by punching that position with a standard card punch. Thus, bits in the microcode word for each word line are defined by the metal pad being present or absent.

The ROS cards were placed in a frame where bit lines ran vertically aligned with each of the 60 columns. A thin sheet of Mylar went between the card and the bit lines to form the capacitive coupling between the metal pad and the word line. The cards were mounted on a 20x12" board with four cards on each side. The mechanics of the boards (ground planes, pressure on the card, insulator thickness, etc.) were such that the coupling ratio between a punched and unpunched pad is at least 10:1. The boards were assembled into a module to form the complete ROS. The Model 30 ROS used 43 boards for a capacity of 4032 60-bit words (with one spare board). The access time for this ROS was 0.75 microsecond.

(Much more about this storage design can be found in J.W.Haskell,Design of a Printed Card Capacitor Read-Only Store, IBM Journal, March 1966.)
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On Display - HLG03 Commissioned By: Museum Until: