IBM NORC - Technology

Technology

The machine originally used electrostatic tubes (CRT or Williams tube) for memory which stored 2000 words, with an access time of 8 microseconds. Each word consisted of 16 decimal digits, using four bits to represent each digit, plus two modulo-4 error-checking bits. A word could store a 13-digit number with sign and 2-digit index, or one instruction. NORC used four sets of 66 electrostatic tubes in parallel for memory. Each of the tubes in a set of 66 stored one bit of each of 500 words, so each of the four sets of 66 tubes stored 500 words. An upgrade to the addressing circuitry for the Williams tubes allowed memory per tube to be expanded from 500 bits to 900 bits, expanding the total memory to 3600 words without needing to add any more Williams tubes.

At some point the Williams tube memory was replaced with 20,000 words of magnetic core memory, with an access time of 8 microseconds.

The speed of the NORC was 15,000 operations per second. An addition took 15 microseconds, a multiplication took 31 microseconds, and a division took 227 microseconds, not counting memory access time and checking. It had the capacity to do double precision arithmetic, which was used occasionally.

The main hardware consisted of 1982 pluggable units, each of which typically had several vacuum tubes plus supporting electronics. There were 62 types of pluggable units, but half of the circuitry used only six of the types and 80% of the circuitry used only 18 of the types. A total of 9800 vacuum tubes and 10,000 crystal diodes were used.

The NORC had eight magnetic tape units which were similar to the tape drives on the IBM 701 system. The reels were 8 inch diameter and somewhat similar in appearance to a metal 16mm film reel.Unlike the 701 series tape drives, there was no operator control panel on the face of the machine, instead there were buttons placed on the top front of the machines that were used to initiate tape loading, rewinding, unloading, etc. The drives could read or write 71,500 characters per second. It had two printers that could print 150 lines per minute, although only one printer could be used at a time. It also had a card reader which could read 100 cards per minute, with four words stored per card. It also had a display unit which consisted of a CRT tube and a 35mm film camera which photographed the face of the tube and then sent the film through a develop and fix process before it was projected on a rear projection screen approximately 12 frames after the initial exposure. High volume data could also be recorded as text on the film, and employees of the Naval Weapons Laboratory would often work overtime in a darkened room scanning the films for obvious recording failures in critical data.