Array Processors in Computer Architecture

Array Processors in Computer Architecture – An array processor or a computer/processor that has an architecture designed for processing a number of arrays. The architecture includes a number of processors (say 64 by 64) working simultaneously, each handling one element of the array, so that a single operation can apply to all elementsof the array in parallel.

To obtain the same effect in a conventional processor, the operation must be applied to each element of the array sequentially, and so consequently much more slowly. An array processor may be built as a self-contained unit attached to a main computer via an I/O port or internal bus; alternatively, it may be a distributed array processor where the processing elements are distributed throughout, and closely linked to, a section of the computer’s memory.

Types of Array Processors

There are basically two types of array processors:

1. Attached Array Processors
2. SIMD Array Processors

Attached Array Processors

An attached array processor is a processor that is attached to a general-purpose computer, and its purpose is to enhance and improve the performance of that computer in numerical computational tasks. It achieves high performance by means of parallel processing with multiple functional units.

In the figure below, the interconnection of an attached array processor to a host computer. A host computer is a general-purpose commercial computer, and the attached processor is a back-end machine driven by the host computer. The array processor is connected through an input-output controller to the computer, and the computer treats it like an external interface. The data for the attached processor are transferred from main memory to a local memory through a high-speed bus.

SIMD Array Processors

SIMD (Single instruction and multiple data) is the organization of a single computer containing multiple processors operating in parallel. The processing units are made to operate under the control of a common control unit. thus providing a single instruction stream and multiple data streams. It contains a set of identical processing elements (PEs), each having a local memory M. Each processor element includes an ALU, a floating-point arithmetic unit, and working registers.

The master control unit controls the operations in the processor elements. The main memory is used for the storage of the program. The function of the master control unit is to decode the instructions and determine the low instruction is to be executed. Scalar and program control instructions are directly executed within the master control unit. Vector instructions are broadcast to all PEs simultaneously.

Each PE used operands stored in its local memory. Vector operands are distributed to the local memories prior to the parallel execution of the instruction. The best-known SIMD array processor is the ILLIAC IV computer developed by the Burroughs Corporation. CM-2, MP-1 is another example of SIMD processors. SIMD processors are highly specialized, and they are not suitable for other types of computations.

Why use the Array Processor

1. Array processors increase the overall instruction processing speed.
2. As most of the Array processors operate asynchronously from the host CPU, it improves the overall capacity of the system.
3. Array Processors has its own local memory, hence providing extra memory for systems with low memory.