Invitation to Computer Science 6th Edition

Chapter 5

Computer Systems Organization

Invitation to Computer Science, 6th Edition 2

Objectives

In this chapter, you will learn about:

• The components of a computer system

• The Von Neumann architecture

• Non-Von Neumann architectures

Introduction

• Computer organization– Branch of computer science that studies computers

in terms of their major functional units and how they work

• Concept of abstraction – Used throughout computer science– Without it, it would be virtually impossible to study

computer design or any other large, complex system

Figure 5.1 The Concept of Abstraction

The Components of a Computer System

• Von Neumann architecture is based on the following three characteristics– Four major subsystems called memory, input/output,

the arithmetic/logic unit (ALU), and the control unit– The stored program concept– The sequential execution of instructions

Figure 5.2 Components of the Von Neumann Architecture

Memory and Cache

• Memory – Functional unit of a computer that stores and

retrieves the instructions and the data being executed

• Random access (RAM)– Access technique used by computer memory

• Read-only memory (ROM)– Information is prerecorded during manufacture

Memory and Cache (continued)

• With a cell size of 8 bits:– The largest unsigned integer value that can be

stored in a single cell is 11111111 (255)

• [0 . . (2N – 1)]– Range of addresses available on a computer

• When dealing with memory:– Distinguish between an address and the contents

of that address

Figure 5.3 Structure of Random Access Memory

Figure 5.4 Maximum Memory Sizes

• Basic memory operations – Fetching and storing

• Memory access time– Typically about 5 to 10 nsec

• Memory registers– Used to implement the fetch and store operations

• Memory Address Register (MAR) – Holds the address of the cell to be fetched or stored

• Memory Data Register (MDR)– Contains data value being fetched or stored

• Two-dimensional structure– Memory organization

• Memory locations – Stored in row major order

• Selection lines– Row selection line– Column selection line

Figure 5.5 Organization of Memory and the Decoding Logic

Figure 5.6 Two-Dimensional Memory Address Organization

• Fetch/store controller– Determines whether we put contents of a memory

cell into the MDR or put the contents of the MDR into a memory cell

• Cache memory– Principle of Locality: when the computer uses

something, it will probably use it again very soon, and it will probably use the “neighbors” of this item very soon

Figure 5.7 Overall RAM Organization

Input/Output and Mass Storage

• Input/output (I/O) units – Devices that allow a computer system to

communicate and interact with the outside world as well as store information

• Volatile memory– Information disappears when power is turned off

• Nonvolatile storage– Role of mass storage devices such as disks and

Input/Output and Mass Storage (continued)

• Input/output devices come in two basic types– Those that represent information in human-readable

form for human consumption– Those that store information in machine-readable

form for access by a computer system

• Disk – Stores information in units called sectors

• Fixed number of sectors are placed in a concentric circle on the surface of the disk, called a track

Figure 5.8 Overall Organization of a Typical Disk

• Seek time– Time needed to position the read/write head over the

correct track

• Latency – Time for the beginning of the desired sector to rotate

under the read/write head

• Transfer time – Time for the entire sector to pass under the

read/write head and have its contents read into or written from memory

• Sequential access storage device (SASD) – Does not require that all units of data be identifiable

via unique addresses

• Direct access storage devices– Much faster at accessing individual pieces of

information

• I/O controller– Has small amount of memory (I/O buffer)– I/O control and logic: ability to handle mechanical

functions of the I/O device

Figure 5.9 Organization of an I/O Controller

The Arithmetic/Logic Unit

• Subsystem that performs addition, subtraction, and comparison for equality

• Components– Registers, interconnections between components,

and the ALU circuitry

• Register – Storage cell that holds the operands of an arithmetic

operation and holds its result

• Bus– Path for electrical signals

Figure 5.10 Three-Register ALU Organization

Figure 5.11 Multiregister ALU Organization

Figure 5.12 Using a Multiplexor Circuit to Select the Proper ALU Result

Figure 5.13 Overall ALU Organization

The Control Unit

• Stored program– Sequence of machine language instructions stored

as binary values in memory

• Control unit– Tasks: fetch, decode, and execute

Machine Language Instructions

• Instructions that can be decoded and executed by the control unit of a computer

• Operation code field – Unique unsigned integer code assigned to each

machine language operation recognized by the hardware

• Address field(s) – Memory addresses of values on which the operation

will work

Figure 5.14 Typical Machine Language Instruction Format

Machine Language Instructions (continued)

• Instruction set– Set of all operations that can be executed by a

processor

• Reduced instruction set computers or RISC machines– Include as little as 30–50 instructions

• Complex instruction set computers (CISC machines)– Include 300–500 very powerful instructions

• Classes of machine language instructions– Data transfer– Arithmetic– Compare– Branch

• Data transfer operations– Move values to and from memory and registers– Instruction Examples: Load X: Load register R with the contents of memory cell X

STORE X: Store the contents of register R into memory cell X

MOVE X Y: Copy the contents of memory cell X into memory cell Y

• Arithmetic/logic operations– Move values to and from memory and registers– Instruction Examples:

ADD X, Y, Z (Three – address instruction)

CON(Z) = CON(X) + CON(Y)

ADD X, Y (Two – address instruction)

CON(Y) = CON(X) + CON(Y)

ADD X (One – address instruction)

R = CON(X) + R

• Compare operations– Compare two values and set an indicator on the basis of

the results of the compare; set status register (or we call condition register, special register) bits

– Instruction Examples: COMPARE X, Y

CON(X) > CON(Y) set GT = 1, EQ = 0, LT = 0

CON(X) = CON(Y) set GT = 0, EQ = 1, LT = 0

CON(X) < CON(Y) set GT = 0, EQ = 0, LT = 1

• Branch operations– Jump to a new memory address to continue processing

– Instruction Examples: JUMP X (unconditionally)

JUMPGT X / JUMPEQ X / JUMPLT X

JUMPGE X / JUMP LE X

Control Unit Registers and Circuits

• Program counter (PC)– Holds the address of the next instruction to be

executed

• Instruction register (IR)– Holds a copy of the instruction fetched from memory

• Instruction decoder– Determines what instruction is in the IR

Figure 5.15 Examples of Simple Machine Language Instruction Sequences

Figure 5.16 Organization of the Control Unit Registers and Circuits

Figure 5.17 The Instruction Decoder

Putting All the Pieces Together–the Von Neumann Architecture

• Program execution phases– Fetch, decode, and execute

• Von Neumann cycle– The repetition of the fetch/decode/execute phase

Figure 5.18 The Organization of a Von Neumann Computer

Figure 5.19 Instruction Set for Our Von Neumann Machine

Non-Von Neumann Architectures

• Problems that computers are being asked to solve – Have grown significantly in size and complexity

• Important limit on increased processor speed – Inability to place gates close together on a chip

• Slowing down– Rate of increase in performance of newer machines

• Von Neumann bottleneck– Inability of the sequential one-instruction-at-a-time

Von Neumann model to handle today’s large-scale problems

Figure 5.20 Graph of Processor Speeds, 1945 to the Present

Non-Von Neumann Architectures (continued)

• Parallel processing– Building computers not with one processor, but with

tens, hundreds, or even thousands

• SIMD parallel processing– ALU is replicated many times– Each ALU has its own local memory where it may

keep private data

• MIMD parallel processing– All processors are replicated– Every processor is capable of executing its own

separate programInvitation to Computer Science, 6th Edition 46

Figure 5.21 A SIMD Parallel Processing System

Non-Von Neumann Architectures (continued)

• Scalability – It is possible to match the number of processors to

the size of the problem• Massively parallel MIMD machines

– Have achieved solutions to large problems thousands of times faster than is possible using a single processor

• Grid computing – Enables researchers to easily and transparently

access computer facilities without regard for their location

Summary of Level 2

• Chapter 4 – Looked at the basic building blocks of computers:

binary codes, transistors, gates, and circuits

• Chapter 5– Examined the standard model for computer design,

called the Von Neumann architecture

• System software– Intermediary between the user and the hardware

components of the Von Neumann machine

Summary

• Computer organization – Examines different subsystems of a computer:

memory, input/output, arithmetic/logic unit, and control unit

• Machine language – Gives codes for each primitive instruction the

computer can perform and its arguments

• Von Neumann machine– Sequential execution of a stored program

• Parallel computers– Improve speed by doing multiple tasks at one time

Invitation to Computer Science 6th Edition

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