IBM 1620
The IBM 1620 was IBM's inexpensive "Scientific Computer" that was introduced in 1960.
It was a variable "word" length decimal (BCD) computer with a memory size that could be 20,000 to 60,000 decimal digits in 20,000 decimal digit increments. While the 5-digit addresses could have addressed 100,000 decimal digits, no machine larger than 60,000 decimal digits was ever built.
Instructions were fixed length (12 decimal digits), consisting of a 2-digit "OP Code", a 5-digit "P Address", and a 5-digit "Q Address".
Fixed point data "words" could be any size from 2 decimal digits up to all of memory not used for other purposes.
Floating point data "words" (using the hardware floating point option) could be any size from 4 decimal digits up to 102 decimal digits (2 digits for the exponent and 2 to 100 digits for the mantissa).
The machine had no programmer accessible registers: all operations were memory to memory (including the index registers of the 1620 II).
There were two models of the 1620:
Available peripherials were:
- IBM 1621 - Paper tape reader
- IBM 1622 - Punch card reader/punch
- IBM 1624 - Paper tape punch
- IBM 1627 - Plotter
- IBM 1311 - Disk drive
- IBM 1443 - Printer, flying type bar
A modified version of the 1620 was used as the CPU of the IBM 1710 Industrial Process Control System.
Development History
The 1620 went through several "Levels" as the implementation changed:
- Model I
- Level A; prototype. All flip flops in the design were transistorized versions of the original Eccles-Jordan trigger circuit. The capacitor coupling used in these proved troublesome in the noisy signal environment of relays and timing cam driven switches used to drive the console typewriter. This necessitated a complete redesign of the machine to use S-R flip flops instead (except for two triggers used to generate clocks for the S-R flip flops). However usage of the term Trigger was retained in all the documentation when referring to a flip flop.
- Level B; first production. This is the only level using a burnished aluminum control panel, later levels finished this panel with white.
- Level C; introduction of 1622 card reader/punch.
- Level D; introduction of 1311 disk drives.
- Level E
- Level F; introduction of Floating Point option.
- Level G; final version of the Model I
- Model II