Xerox 500 series

The Xerox 500 series was a line of computers from Xerox Data Systems (XDS) introduced in the early 1970s as backward-compatible upgrades for the Sigma series machines. The systems had failed to gain traction by the time Xerox sold its Data Systems Division in 1975. The buyer, Honeywell, Inc., continued to support existing 500-series systems until 1984 but discontinued manufacturing.

The Xerox 530 system was a 16-bit computer aimed at upgrading the 16-bit Sigma 2 and 3 systems. The 530 was the first system of the line introduced in early 1973. The Xerox 550 and Xerox 560 systems were 32-bit computers introduced in 1974. The 550 was aimed at real-time applications and intended as an upgrade for the Sigma 5. The 560 was aimed at the general-purpose Sigma 6, 7, and 9 upgrade market. A 590 system was designed but never built.

The systems were microprogrammed and constructed using large-scale and medium-scale integration (LSI and MSI) and magnetic-core memory. They featured independent Input/Output Processors (IOP), and "Direct Control" instructions for direct input/output of a single word via a parallel interface

The 530 supported memory sizes of 8 K to 64 K 16-bit words (16 KB to 128 KB) with a cycle time of 800 ns. The memory protection feature protected the foreground (real-time) program from the background tasks.

The 550 and 560 supported 16 K to 256 K 32-bit words (64 KB to 1 MB) . Main memory cycle time was 645 ns. Virtual memory and memory protection were standard features.

Binary integer arithmetic was standard on all models; floating-point was optional on the 530, and standard on the 550 and 560. The 560 also supported decimal arithmetic. The 550 and 560 included one or more "system control processors" (CPs) to handle interrupts, diagnostics, clocks, direct I/O, and operator communications. Systems were clusterable, with multiple "basic processors" (BPs), I/O processors (IOPs), and "system control processors" (CPs) sharing busses and memory.

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