Array Processor

Array Processor

• An array processor is synchronous parallel computer with multiple arithmetic logic units. These arithmetic logic units are also known as processing elements (PE), which can operate in parallel in a lock step fashion. By replication of ALUs the array processors can achieve the spatial parallelism. As PEs are synchronized to perform the same function at the same time, the array processor can handle single instruction and multiple data streams. Because of this reason, array processors are also known as SIMD processors.

1. SIMD Array Processor

• Fig. 10.7.1 shows the typical functional structure of an SIMD array processor. As shown in Fig. 10.7.1, all PEs are synchronized and controlled by single control unit. Each PE is an ALU with attached working registers and local memory. The PEs are interconnected by a data–routing network. The control unit (CU) consists of control processor (CP) and control memory (CM). The system and user programs are executed under control of CU. The user programs are loaded into CU memory from an external source.

• The function of CU is to decode all the instructions and determine where the decoded instructions should be executed.

■ Scalar instructions – Executed directly inside the CU

■ Vector instructions – They are broadcast to PEs for through duplicate arithmetic units (PEs)

• All the PEs perform the same function synchronously in a lock step fashion under the command of CU. Vector operands are distributed to PE memories before parallel execution in the array of PEs. The distributed data can be loaded into PE memories from an external source via system data bus or via CU in a broadcast mode using control bus. Masking schemes are used to control the status of each PE during execution of vector instruction. A masking vector is used to control the status of all PEs. In other words not all PEs need to participate in the execution of vector instruction.

2. Attached Array Processor

• To enhance the performance of conventional computer and to provide vector processing capability for complex scientific applications, the array processor can be attached to a conventional computer as a peripheral. Due to such attachment the performance of conventional computer improves a lot because of parallel processing support given by array processor with multiple functional units.

• Fig. 10.7.2 shows the interface between the attached array processor and the conventional computer. The array processor is connected to the conventional computer through an input output controller. Usually, a local memory is available for array processor. The data for array processor is transferred to local memory from the main memory through high speed bus.

Review Questions

1. What is an array processor ?

2. Draw and explain the typical functional structure of a SIMD array processor.

3. Write a short note on attached array processor.

4. What is an array processor? Explain the different types of array processor.

5. What is array processors? Explain attached array processors and SIMD array processors.