UNIVAC Solid State

The UNIVAC Solid State was a magnetic drum-based solid-state computer announced by Sperry Rand in December 1958 as a response to the IBM 650. It was one of the first computers to be (nearly) entirely solid-state, using 700 transistors, and 3000 magnetic amplifiers (FERRACTOR) for primary logic, and 20 vacuum tubes largely for power control. It came in two versions, the Solid State 80 (IBM-style 80 column cards) and the Solid State 90 (Remington-Rand 90 column cards). In addition to the "80/90" designation, there were two variants of the Solid State -- the SS I 80/90 and the SS II 80/90. The SS II series included two enhancements -- the addition of 1,280 words of core memory and support for magnetic tape drives. The SS I had only the standard 5,000-word drum memory described in this article and no tape drives.

Both variants included a card reader, a card punch, and the line printer described in this article. The only "console" was a 10-key adding machine-type keypad, from which the operator would enter the commands to boot the computer. That keypad was also used by programmers in the debugging process. There was no Operating System as we have come to know them in recent years; every program was completely self-contained, including the boot loader that initiated execution. All programs were loaded from punched cards; even on the SS II, with its tape drives, there was no ability to launch programs from those drives.

The UNIVAC Solid State was a 2-address, bi-quinary coded decimal computer using signed 10 digit words. Main memory storage was provided by a 5000-word magnetic drum spinning at 17,667 RPM in a helium atmosphere. For efficiency, programmers had to take into account drum latency, the time required for a specific data item, once written, to rotate to where it could be read.

The Solid State was one of the first computers to use some solid-state components. However, much of the computer's logic was made out of magnetic amplifiers, not transistors. The decision to use magnetic amplifiers was made because the point-contact germanium transistors then available had highly variable characteristics and were not sufficiently reliable. The magnetic amplifiers were based on tiny (about 1/8" ID) toroidal stainless steel spools wound with two or so layers of 1/32" wide 4-79 moly-permalloy magnetic material to form magnetic cores. These cores had two windings of #60 copper wire surrounding the 4-79 molypermalloy.

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