Primary & Secondary Memory, Lecture notes of Computer Science

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• Ref Page Chapter 7: Processor and Memory Slide 1/

Ref Page Chapter 7: Processor and Memory Slide 2/

In this chapter you will learn about:

§ Internal structure of processor

§ Memory structure

§ Determining the speed of a processor

§ Different types of processors available

§ Determining the capacity of a memory

§ Different types of memory available

§ Several other terms related to the processor and

main memory of a computer system

Learning Objectives Learning Objectives

Ref Page Chapter 7: Processor and Memory Slide 4/

§ The brain of a computer system

§ Performs all major calculations and comparisons

§ Activates and controls the operations of other units of a

computer system

§ Two basic components are

§ Control Unit (CU)

§ Arithmetic Logic Unit (ALU)

§ No other single component of a computer determines

its overall performance as much as the CPU

Central Processing Unit (CPU) Central Processing Unit (CPU)

Ref Page Chapter 7: Processor and Memory Slide 5/

§ One of the two basic components of CPU

§ Acts as the central nervous system of a computer

system

§ Selects and interprets program instructions, and

coordinates execution

§ Has some special purpose registers and a decoder to

perform these activities

Control Unit (CU) Control Unit (CU)

Ref Page Chapter 7: Processor and Memory Slide 7/

§ CPU has built-in ability to execute a particular set of machine instructions, called its instruction set § Most CPUs have 200 or more instructions (such as add, subtract, compare, etc.) in their instruction set § CPUs made by different manufacturers have different instruction sets § Manufacturers tend to group their CPUs into “families” having similar instruction sets § New CPU whose instruction set includes instruction set of its predecessor CPU is said to be backward compatible with its predecessor

Instruction Set Instruction Set

Ref Page Chapter 7: Processor and Memory Slide 8/

§ Special memory units, called registers, are used to

hold information on a temporary basis as the

instructions are interpreted and executed by the CPU

§ Registers are part of the CPU (not main memory) of a

computer

§ The length of a register, sometimes called its word

size , equals the number of bits it can store

§ With all other parameters being the same, a CPU with

32-bit registers can process data twice larger than

one with 16-bit registers

Registers Registers

Ref Page Chapter 7: Processor and Memory Slide 10/

§ Computer has a built-in system clock that emits millions of regularly spaced electric pulses per second (known as clock cycles) § It takes one cycle to perform a basic operation, such as moving a byte of data from one memory location to another § Normally, several clock cycles are required to fetch, decode, and execute a single program instruction § Hence, shorter the clock cycle, faster the processor § Clock speed (number of clock cycles per second) is measured in Megahertz (10^6 cycles/sec) or Gigahertz (10^9 cycles/sec)

Processor Speed Processor Speed

Ref Page Chapter 7: Processor and Memory Slide 11/

Mostly used in workstations

§ Small instruction set § Fixed-length instructions § Reduced references to memory to retrieve operands

RISC (Reduced Instruction Set Computer)

Mostly used in personal computers

§ Large instruction set § Variable-length instructions § Variety of addressing modes § Complex & expensive to produce

CISC (Complex Instruction Set Computer)

Type of Features Usage Architecture

Types of Processor Types of Processor

(Continued on next slide)

Ref Page Chapter 7: Processor and Memory Slide 13/

Mostly used in high-end servers and workstations

§ Processor chip has multiple cooler-running, more energy- efficient processing cores § Improve overall performance by handling more work in parallel § can share architectural components, such as memory elements and memory management

Multi-Core Processor

Type of Features Usage Architecture

Types of Processor Types of Processor

(Continued from previous slide..)

Ref Page Chapter 7: Processor and Memory Slide 14/

§ Every computer has a temporary storage built into

the computer hardware

§ It stores instructions and data of a program mainly

when the program is being executed by the CPU.

§ This temporary storage is known as main memory,

primary storage, or simply memory.

§ Physically, it consists of some chips either on the

motherboard or on a small circuit board attached to

the motherboard of a computer

§ It has random access property.

§ It is volatile.

Main Memory Main Memory

Ref Page Chapter 7: Processor and Memory Slide 16/

Addresses of a memory

The words of a memory (total N words)

N-

N-1 Each word contains the same number of bits = Bit 1 Bit 2 word length

Main Memory Organization Main Memory Organization

(Continued on next slide)

Ref Page Chapter 7: Processor and Memory Slide 17/

§ Machines having smaller word-length are slower in

operation than machines having larger word-length

§ A write to a memory location is destructive to its previous

contents

§ A read from a memory location is non-destructive to its

previous contents

Main Memory Organization Main Memory Organization

(Continued from previous slide..)

Ref Page Chapter 7: Processor and Memory Slide 19/

B O M B A Y

0025 0026

0027

0028

0029 0030

0031

4096

D

E

L

H

I

0051

0052

0053 0054

0055

0056

4096

§ Each memory location can store only a single character

§ Slower in speed of calculation than fixed world-length memory

§ Used in small business computers for optimizing the use of storage space

Note: With memory becoming cheaper and larger day-by-day, most modern computers employ fixed-word-length memory organization

Variable Word-length Memory Variable Word-length Memory

Address Numbers

Address Numbers

Ref Page Chapter 7: Processor and Memory Slide 20/

§ Memory capacity of a computer is equal to the number

of bytes that can be stored in its primary storage

§ Its units are:

Kilobytes (KB) : 1024 (2^10 ) bytes

Megabytes (MB) : 1,048,576 (2^20 ) bytes

Gigabytes (GB) : 1,073,741824 (2^30 ) bytes

Memory Capacity Memory Capacity