Microprocessor Basics


Microprocessor Basics:
A microprocessor is a semiconductor chip, which is manufactured using the Large Scale integration
(LSI) or Very Large Scale Integration (VLSI), which comprises Arithmetic Logic Unit, Control unit and
Central Processing Unit (CPU) fabricated on a single chip.


Instruction Set: It is the set of instructions that the microprocessor executes

Word Length: The number of bits processed in a single instruction is called word length or word size. The word size is directly proportional to the processing power of the CPU. During the processing, the internal general purpose registers hold data. So if internal registers can hold data upto 8 bits, the word length is 8 bits. If it can process 16 bits at a time, then the internal registers can hold upto 16 bits at a time and so on. Hence a 32 bit processor is about 4 times faster than an 8 bit processor. Examples of word lengths are 16 bit, 32 bit, 64 bit. The terms 16-bit CPU, 32-bit CPU, 64-bit CPU are used very often while talking about CPUs. Now  we know that these terms mean the maximum number of bits a given CPU can handle at a time.

Registers: A register is a very small amount of very fast memory that is built into the CPU (central
processing unit) in order to speed up its operations by providing quick access to commonly used values. All data must be represented in a register before it can be processed. For example, if two numbers are to be multiplied, both numbers must be in registers, and the result is also placed in a register.

A collection of wires through which data is transmitted from one part of a computer to another. You can think of a bus as a highway on which data travels within a computer. When used in reference to personal computers, the term bus usually refers to internal bus. This is a bus that connects all the internal computer components to the CPU and main memory. All buses consist of two parts — an address bus and a data bus. The data bus transfers actual data whereas the address bus transfers information about where the data should go. The control bus is used by the CPU to direct and monitor the actions of the other functional areas of the computer. It is used to transmit a variety of individual signals (read, write, interrupt, acknowledge, and so forth) necessary to control and coordinate the
operations of the computer. The size of a bus, known as its width, is important because it determines how much data can be transmitted at one time. For example, a 16-bit bus can transmit 16 bits of data, whereas a 32-bit bus
can transmit 32 bits

Clock speed: Also called clock rate, the speed at which a microprocessor executes instructions. Every computer contains an internal clock that regulates the rate at which instructions are executed and synchronizes all the various computer components. The CPU requires a fixed number of clock ticks (or clock cycles) to execute each instruction. The faster the clock, the more instructions the CPU can execute per second. Clock speeds are expressed in megahertz (MHz) or gigahertz ((GHz).

16 bit Microprocessor: It indicates the width of the registers. A 16-bit microprocessor can process data and memory addresses that are represented by 16 bits. Eg. 8086 processor

32 bit Microprocessor: It indicates the width of the registers. A 32-bit microprocessor can process data and memory addresses that are represented by 32 bits. Eg. Intel 80386 processor, Intel 80486

64 bit Microprocessor: It indicates the width of the registers; a special high-speed storage area within the CPU. A 32-bit microprocessor can process data and memory addresses that are represented by 32 bits. Eg. Pentium dual core, core 2 duo.

128 bit Microprocessor: It indicates the width of the registers. A 128-bit microprocessor can process data and memory addresses that are represented by 128 bits. Eg. Intel core i7

Classification of Microprocessors

RISC (Reduced Instruction Set Computing):

It stands for Reduced Instruction Set Computer. It is a type of microprocessor architecture that uses a small set of instructions of uniform length. These are simple but primitive instructions which execute in one clock cycle. For
this reason, RISC chips are less complex and also less expensive to produce. The instructions are of uniform length which interface with about 32-36 registers. The program size in case of RISC architecture is more but more memory cycles are needed to access data. To reduce the number of memory cycles, RISC keeps the necessary data in the processor itself. The drawback of RISC design is that the computer must combine or repeat operations to complete a large program consisting of many processing operations. Since instructions are simple , RISC processors are relatively simple to design. Examples of RISC processor is SPARC, POWER PC etc.

CISC (Complex Instruction Set Computing):
It stands for Complex Instruction Set Computer. A CISC chip such as Intel Pentium provides programmers with hundreds of instructions of variable sizes, and the processing circuitry includes many special purpose circuits that carry out these instructions at high speeds. These instructions interface with memory in multiple mechanisms with complex addressing modes. In this case the program size is reduced and hence lesser number of memory cycles are required to execute

EPIC (Explicitly Parallel Instruction Computing):
It is a 64-bit microprocessor instruction set, jointly defined and designed by Hewlett Packard and Intel,
that provides up to 128 general and floating point unit registers and uses speculative loading,
predication, and explicit parallelism to accomplish its computing tasks. By comparison, current 32-bit
CISC and RISC microprocessor architectures depend on 32-bit registers, branch prediction, memory
latency, and implicit parallelism, which are considered a less efficient approach in microarchitecture

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