UNIVAC 1100

The UNIVAC 1100/2200 series is a series of compatible 36-bit computer systems, beginning with the UNIVAC 1107 in 1962, initially made by Sperry Rand. The series continues to be supported today by Unisys Corporation as the ClearPath Dorado Series. The solid-state 1107 model number was in the same sequence as the earlier vacuum-tube computers, but the early computers were not compatible with the solid-state successors. The model numbers are based on the binary number system.

Instructions are 36 bits long with the following fields:

The 128 registers of the high-speed "general register stack" ("integrated circuit registers" on the UNIVAC 1108 and UNIVAC 1106 models), map to the current data space in main storage starting at memory address zero. These registers include both user and executive copies of the A, X, R, and J registers and many special function executive registers.

The table on the right shows the addresses (in octal) of the user registers.

There are 15 index registers (X1 ... X15), 16 accumulators (A0 ... A15), and 15 special function user registers (R1 .. R15). The 4 J registers and 3 "staging registers" are uses of some of the special function R registers.

One interesting feature is that the last four index registers (X12 ... X15) and the first four accumulators (A0 ... A3) overlap, allowing data to be interpreted either way in these registers. This also results in four unassigned accumulators (A15+1 ... A15+4) that can only be accessed by their memory address (double word instructions on A15 do operate on A15+1).

Prior to the UNIVAC 1107, UNIVAC produced several vacuum-tube-based machines with model numbers from 1101 to 1105. These machines had different architectures and word sizes and were not compatible with each other. They all used vacuum tubes and many used drum memory as their main memory. Some were designed by Engineering Research Associates (ERA) which was later purchased and merged with the UNIVAC company.

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