02 inside the computer

8/12/2019 02 Inside the Computer

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INSIDE THE COMPUTER


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Some important terminology

Amounts of memory

Bit A binary digit that can have the value 0 or 1

Byte Defined as 8 bits

Nibble Half a byte

4 bits

Word Two bytes

16 bits


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Kilobyte (K)

bytes

1024 bytes

Megabyte (M) bytes

Over 1 million bytes

1,048,576 Gigabyte (G)

bytes

Over 1 billion

102

202

302


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Terabyte (T)

bytes

Over 1 trillion

Example:

16 megabyte of memory

= 16 x

= x

= bytes

402

202

42

202

242


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Two types of memory

RAM

Random Access Memory

Read / Write memory

Temporary storage of programs that it is running

Data is lost when the computer is turned off

Volatile memory


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Two types of memory

ROM

Read-Only Memory

Contains program and inform essential to

operation of the computer

Information stored is permanent / cannot be

change by the user / not lost when the power is

turned off

Nonvolatile memory


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Internal organization of computers

Internal parts of the computer

Central Processing Unit (CPU)

Execute (process) information stored in memory

Memory

Information is stored

Input / Output

Provide a means of communicating with the CPUe.g. keyboard and video monitor


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Three types of buses:

Address bus

Data bus

Control bus

Memory Address

For a device (memory or I/O) to be

recognized by the CPU, it must be assignedan address

Address in a given device must be unique

Uses the address bus


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Control Bus

Used to provide read or write signals to the

device to indicate if the CPU is asking for

information or sending it information


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More about the data bus

Used to carry information in and out of aCPU, the more data buses available, thebetter but more expensive the CPU

Average size of data buses in CPU 8(Apple 2) and 64 (Cray) / bidirectional

The processing power of a computer is

related to the size of its busesExample:

8 bits can send 1 byte at a time

16 bits can send 2 bytes at a time


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More about the address bus

Used to identify the devices and memory

connected to the CPU, the more address

buses available, the larger the number of

devices that can be addressed

The number of locations is equal to

where x is the number of address lines,

regardless of the size of the data bus

x

2


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More about the address bus

Example:

A CPU with 16 address lines

= 65,536 bytes= bytes

= 64K bytes

Each location can have a maximum of 1byte of data (byte addressable)

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CPU and its relation to RAM and

ROM

ROM

Provide information that is fixed and

permanent

Tables for character patterns to be displayed onthe video monitor

Programs that are essential to the working of the

computer

Programs for testing and finding the total amount of RAMinstalled in the system

Programs to display information on the video

monitor


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ROM

RAM

Used to store information that is not

permanent and can change with time

Various versions of the operating system

Application packages

Word processing

Tax calculation packages


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ROM


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Inside CPUs

Registers

Used to store information temporarily

Data / Instructions

Memory Address

8-bit, 16-bit, 32-bit, and 64-bit

ALU (arithmetic / logic unit)

Responsible for performing Arithmetic functions such as add, subtract,

multiply, and divide

Logic functions such as AND, OR, and NOT


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Inside CPUs

Program Counter

It point to the address of the next instruction to be

executed. As each instruction is executed, the

program counter is incremented to point to the

address of the next instruction to be executed

IBM (Instruction Pointer)

Instruction Decoder

It interpret the instruction fetched into the CPU Like the dictionary, it stores the meaning of each

instruction and what steps the CPU should take upon

receiving a given instruction


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Internal working of computers

Example:

Imaginary CPU has registers A, B, C, and D

Has 8-bit data bus and 16-bit address bus

CPU can access memory from 0000 to FFFF

Assume the CPU will put 21H into register A,

and then add to register A values 42H and 12H

Assume that the code for moving a value toregister A is 1011 0000 (B0H)

Adding a value to register A 0000 0100 (04H)


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Example:

Equivalent Code:

Action Code Data

Move value 21H into register A B0H 21H

Add value 42H to register A 04H 42H

Add value 12H to register A 04H 12H


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Example:

If the program to perform the actions is stored in

memory locations starting at 1400H

Memory Address Contents of memory address

1400 (B0) the code for moving a value to register A

1401 (21) the value to be moved

1402 (04) the code for adding a value to register A

1403 (42) the value to be added

1404 (04) the code for adding a value to register A

1405 (12) the value to be added

1406 (F4) the code for halt


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Example:

CPU Actions

1. IP = 1400H

2. 1400H -> address busREAD signal is activated

B0H -> data bus

3. B0H is decoded using decoder dictionary

1401H -> address busREAD signal is activated

21H -> data bus -> register A


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4. IP = 1402H

READ signal is activated

04H -> data bus

04H is decoded using decoder dictionary1403H -> address bus


42H -> data bus

ALU performs addition 42H + 21H = 63H

63H -> register A


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5. IP = 1404H


04H -> data bus

04H is decoded using decoder dictionary

1405H -> address bus


12H -> data bus

ALU performs addition 63H + 12H = 75H

63H -> register A


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6. IP = 1406


F4H -> data busF4H is decoded using decoder dictionary

IP will stop incrementing


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END


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BRIEF HISTORY OF THE

CPU(Next Topic)


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Exercises

1. How many bytes is 24 kilobytes?

2. What does RAM stand for? How is it

used in computer system?

3. What does ROM stand for? How is it

used in computer system?

4. Why is RAM called volatile memory?

5. List the three major components of a

computer system.


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Exercises

6. What does CPU stand for? Explain its function in acomputer.

7. List three types of buses found in computer systemsand state briefly the purpose of each type of bus.

8. State which of the following is unidirectional and whichis bidirectional.

a) Data bus

b) Address bus

9. If an address bus for a given computer has 16 lines,then what is the maximum amount of memory it canaccess?

10. What does ALU stand for? What is its purpose?


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Exercises

11.How are registers used in computer

systems?

12.What is the purpose of the program

counter?

13.What is the purpose of the instruction

decoder?

02 inside the computer

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