Types of Microprocessors:

To know about the types of microprocessor lets know what is a microprocess its use and feature evolution. Part 1: Introduction to Microprocessor Evolution with features. Some of the types are discussed with real time use examples:

Vector Processors

For vector computations this kind of processor was designed. A vector is an array of operands of the same type. Consider the following vectors:

Vector A (a1, a2, a3, ……., an)
Vector B (b1, b2, b3,……., bn)
Vector C = Vector A + Vector B
= C(c1, c2, c3, …….,cn), where c1 = a1+ b1, c2 = a2 + b2, …..,Cn= an + bn.

A vector processor adds all the elements of vector A and Vector B using a single vector instruction with hardware approach.

Examples:

DEC’s VAX 9000, IBM 390/VF,CRAY Research Y-MP family, and Hitachi’s S-810/20, etc.

Array Processors or SIMD Processors:

This Array processors are also designed for vector computations. The key difference between an array processor and a vector processor is  a vector processor uses multiple vector pipelines, on the other hand an array processor deploys a number of processing elements to operate in parallel. An array processor contains multiple numbers of ALUs. Each ALU is provided with the local memory. The ALU together with the local memory is called a Processing Element (PE). An array processor is a SIMD (Single Instruction Multiple Data) processor. So using a single instruction, the same operation can be performed on an array of data which makes it suitable for vector computations.

Types of Microprocessors

Scalar and Superscalar Processors:

A processor  executes scalar data is called scalar processor. The simplest scalar processor makes processing of only integer instruction using fixed-points operands. A powerful scalar processor makes processing of both integer as well floating- point numbers. It contains an integer ALU and a Floating Point Unit (FPU) on the same CPU chip.

A scalar processor may be RISC processor or CISC processor.

Examples of CISC processors are:  Intel 386, 486; Motorola’s 68030, 68040; etc.
Examples of RISC scalar processors are: Intel i860, Motorola MC8810, SUN’s SPARC CY7C601, etc.

A superscalar processor has multiple pipelines and executes more than one instruction per clock cycle. Examples of superscalar processors are: Pentium, Pentium Pro, Pentium II, Pentium III, etc.

Other Three Types of Microprocessors namely, CISC, RISC, and EPIC.

They are as follows:

1. CISC (Complex Instruction Set Computer)

As the name suggests, the instructions are in a complex form. It means that a single instruction can contain many low-level instructions. For example loading data from memory, storing data to the memory, performing basic operations, etc. Besides, we can say that a single instruction has multiple addressing modes. Furthermore, as there are many operations in single instruction they use very few registers.

Examples of CISC are: Intel 386, Intel 486, Pentium, Pentium Pro, Pentium II, etc.

2. RISC (Reduced Instruction Set Computer)

As per the name, in this, the instructions are quite simple, and hence, they execute quickly. Moreover, the instructions get complete in one clock cycle and also use a few addressing modes only. Besides, it makes use of multiple registers so that interaction with memory is less.

Examples are IBM RS6000, DEC Alpha 21064, DEC Alpha 21164, etc.

3. EPIC (Explicitly Parallel Instruction Computing)

It allows the instructions to compute parallelly by making use of compilers. Moreover, the complex instructions also process in fewer clock frequencies. Furthermore, it encodes the instructions in 128-bit bundles. Where each bundle contains three instructions encoded in 41 bits each and a 5-bit template. This 5-bit template contains information about the type of instructions and that which instructions can be executed in parallel.

Examples are IA-64 (Intel Architecture-64), etc.

Characteristics of CISC are as follows:

• As the instructions are complex hence, the decoding of instructions is also complex.
• The size of instructions is greater than the one-word size.
• Instruction can take more than one clock cycle to execute.
• The number of registers is less since most of the operations are performed in memory itself.
• The address modes are also complex.
• Data types are more in number.

Characteristics of RISC are as follows:

• As the instruction is simple hence, the decoding of instructions is also simple
• The size of instructions is under the one-word size.
• Instruction takes one clock cycle to execute.
• The number of registers is more.
• The address modes are also simple.
• Here, Data types are less in number.
• It Can be used for pipelining.

Advantages of CISC are as follows:

Microprogramming in CISC is as easy as the assembly language implementation. The number of instructions for performing operations is less in number. Hence, the memory usage is low. Moreover, time consumption is also less.

Advantages of RISC are as follows:

Instructions are simple hence easy to understand and decode. The instructions complete in one clock cycle therefore, CPU can handle multiple instructions at a time. Designing the RISC processors is easier in comparison to the CISC processors.

Key difference between RISC and CISC

Digital Signal Processors (DSP):

DSP microprocessors specifically designed to process signals. They receive some digitized signal information, perform some mathematical operations on the information and give the result to an output device. They implement integration, differentiation, complex fast Fourier transform, etc. using hardware.

Examples of digital signal processors are:

Texas instruments’ TMS 320C25, Motorola 56000, National LM 32900, Fujitsu MBB 8764, etc.

Symbolic Processors

Symbolic processors are designed for expert system, machine intelligence, knowledge based system, pattern-recognition, text retrieval, etc. The basic operations which are performed for artificial intelligence are: Logic interference, compare, search, pattern matching, filtering, unification, retrieval, reasoning, etc. This type of processing does not require floating point operations. Symbolic processors are also called LISP processors or PROLOG processors.

Bit-Slice Processors:

The processor of desired word length is developed using the building blocks. The basic building block is called Bit-Slice where the building blocks include 4-bit ALUs, micro programs sequencers, carry look-ahead generators, etc. The word ‘slice’ was used because the desired number of ALUs and other components were used to build an 8-bit, 16-bit or 32-bit CPU.

Examples of Bit-Slice Processors were:

AMD-2900, AMD 2909, AMD 2910, AMD 29300 series, Texas instrument’s SN-74AS88XX series, etc.

Transputers

In a multiprocessor system, a transputer is a specially designed microprocessor to operate as a component processor. Transputers were introduced in late 1980’s. They were built on VLSI chip and contained a processor, memory and communication links. The communication link was to provide point-to-point connection between transputers. A transputer contains FPU, on-chip RAM, high-speed serial link, etc.

Examples of transputers are: INMOS T414, INMOS T800, etc. Where, T414 was a 32-bit processor with 2 KB memory. The T800 was FPU version of 32-bit transputer with 4 KB memory.

Graphic Processors

Graphics Processors are specially designed processors for graphics. Intel has developed Intel 740-3D graphics chip. It is optimized for Pentium II PCs, using a hyper pipelined 3D architecture with additional 2D acceleration. Like most 3D graphics chips, the I-740 will be marketed in performance, not the main stream category. It is designed mostly for such heavy multimedia uses as games and movies.