IBM 3081

The IBM Model 3081 Processor Complex was a mainframe computer which was announced November 12, 1980 and withdrawn August 4, 1987. It introduced the System/370 Extended Architecture. (IBM c. 1982) It consisted of a 3081 Processor Unit and supporting units; the 3083 and 3084 were in the same family. (IBM 1982; Pittler, Powers, and Schnabel 1982).

Some key technological features of the 3081—compared to the previous most powerful processor, the 3033—were the following:

• About 800,000 circuits implemented in large scale integration, using up to 704 logic circuits per chip, which provided the required performance, reliability, and serviceability that were design goals
• "Elimination of one complete level of packaging—the card level" (p. 2)
• Water cooling, which provides heat removal from chips beyond the ability of conventional air cooling
• A machine cycle time of 26 nanoseconds (38 MHz equivalent CPU)
• Reduced power consumption, 23 kilowatts for a 3081-D16 versus 68 kilowatts for a 3033-U16
• Approximately double the instruction-execution rate of the 3033
• Two central processor components (Pittler, Powers, and Schnabel 1982, 2, 3, 8)

Both central processors have access to channels (as many as 24), and main memory (up to 32 megabytes). (Pittler, Powers, and Schnabel 1982, 3, 4)

The elimination of a layer of packaging was achieved through the development of the Thermal Conduction Module (TCM), a flat ceramic module containing about 30,000 logic circuits on up to 118 chips. The TTL chips (which were not compatible with the TTL chips sold on the open market by many manufacturers) were joined face-down (sometimes called "flip chip") to the TCM with an array of 11 × 11 solder pads. The TCM contains 33 metalized layers which distribute signals and power. "A module is connected to the next level of packaging through 1800 pins (1200 are available for signals, 500 pins are available for power, and 100 pins are spare)." (p. 7) The module is fitted with a helium-filled metal cap, which contains one piston per chip; the piston presses against the back of each chip to provide a heat conduction path from the chip to the cap. A water-cooled cold plate is attached to the cap; the water temperature is approximately 24 °C. This arrangement provides cooling of the module heat flux on the order of 10⁵ watts per square meter, which is about a tenfold increase over the 3033 processor. (Pittler, Powers, and Schnabel 1982, 4–8)

The internal code name of the 3081 was Adirondack. (Congressional Record 1989)