FPS AP-120B

The FPS AP-120B was a 38-bit, pipeline-oriented array processor manufactured by Floating Point Systems. It was designed to be attached to a host computer such as a DEC PDP-11 as a fast number-cruncher. Data transfer was accomplished using direct memory access.

Processor cycle time was 167 nanoseconds, giving a speed of 6 MHz. Since it could present two floating point results per cycle, one from the adder and the other from the multiplier, a capacity of 12 Megaflops was claimed for the processor.

Architecture

The processor was designed around the concept of multiple parallel processing units operating in synchronization. A single 64-bit instruction word was divided into fields, each of which instructed a particular module under the control of the CPU. The modules were as follows:

• 16-bit Arithmetic and Logic unit (ALU)
• 38-bit Floating Point Adder (FADD) (two stages)
• 38-bit Floating Point Multiplier (FMUL) (three stages)
• Two Data Pad registers for receiving data from memory.

The processor had access to dual-interleaved core memory in which odd numbered addresses were stored in one physical bank, and even numbered addresses were stored in the other. This represented an attempt to take advantage of typical sequential fetching of memory words. Fetching sequentially from one physical bank would result in a latency of two instruction cycles before the data was loaded into the destination data pad. Interleaving allowed a sequential access to occur immediately after...
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