Instructions are 36 bits long with the following fields:
|014||X12/A0||Overlap (X or A)|
|...||...||Overlap (X or A)|
|017||X15/A3||Overlap (X or A)|
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 4 index registers (X12 ... X15) and the first 4 accumulators (A0 ... A3) overlap, allowing data to be interpreted either way in these registers. This also results in 4 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).
In 1996 Unisys introduced the ClearPath IX series. The ClearPath machines are a common platform that implement either the 1100/2200 architecture (the ClearPath IX series) or the Burroughs large systems architecture (the ClearPath/MCP series). Everything is common except the actual CPUs, which are implemented as ASICs. In addition to the IX (1100/2200) CPUs and the MCP (burroughs large systems) CPU, the architecture had Xeon (and briefly Itanium) CPUs. Unisys' goal was to provide an orderly transition for their 1100/2200 customers to a more modern architecture.
US Patent Issued to International Business Machines on Sept. 14 for "Method, System, and Computer Program Product for Path-Correlated Indirect Address Predictions" (Minnesota, New York Inventors)
Sep 15, 2010; ALEXANDRIA, Va., Sept. 20 -- United States Patent no. 7,797,521, issued on Sept. 14, was assigned to International Business...
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Feb 20, 2012; ALEXANDRIA, Va., Feb. 20 -- United States Patent no. 8,117,347, issued on Feb. 14, was assigned to International Business...