Computer Organization

Prepared by: Anh Q. VuCourse: CS-147Professor: Sin-Min LeeDate: Summer - 2001

Computer Organization

Contents (Text Book: page 142 – 158)

1. Overview2. Computer Organization3. Definitions - Buses4. Computer Organization Diagram5. CPU organization Diagram6. Memory7. Memory Chip Organization8. The Instruction Cycle9. Supporting Diagrams

(25 minutes)

Computer Organization“Overview”

The Intel Microprocessor Evolution Microprocessor Year introduced # of

Transistors 8008 1972 3000 8080 1974 4500 8085 1976 6500 8086 1978 29,000 8088 1979 29,000 80286 1982 130,000 80386 1985 275,000 80486 1989 1.2 million Pentium 1992 3.1 millionPentium Pro 1995 5.5 millionPentium III 1999 9.5 millionPentium 4 2000 42 million

Computer Organization

Computer Organization

• A computer is organized into 3 internal parts:

1. CPU2. Memory3. I/O (Input/Output)

Computer Organization

1. CPU – It is the Central Processing Unit of the

computer.– Its function is to execute or process the

information stored in memory.– The CPU is connected to memory and I/O

through strips of wire called bus.

Computer Organization

2. Memory – Memory is the big store house of data located

within the main computer outside of the Microprocessor.

Computer Organization

3. I/O (Input/Output)

– Input devices provide signals to the CPU.» Keyboard, Sensors, Switches, etc.

– Output devices take signals from the CPU and perform required actions.

» Printers, Monitor, Lights, etc.

Computer OrganizationBUS

• Bus– Bus is a set of wires that connects the CPU to

memory and I/O– It carries information from place to place just as a

street bus carries people from place to place. – There are 3 types of bus

» Address bus» Data bus» Control bus

Computer OrganizationBUS cont.

a) Address bus– Address bus is the set of wires that carries addresses

of memory or I/O only.– For a memory or I/O to be recognized by the CPU it

must be assigned an address.– The assigned address must be unique; no two devices

are allowed to have the same address.– The CPU puts the address on the address bus, and the

decoding circuitry finds the device.

Computer OrganizationBUS cont.

b) Data bus– Data bus is a set of wires that carries data only.– After finding the device through the address

bus, the CPU uses the data bus either to get data or to send data to the device.

Computer OrganizationBUS cont.

c) Control bus– Control bus is a set of wires that carries control

signals only.– The control buses are used to provide read or

write signals to the device to indicate if the CPU is asking or sending information.

Computer OrganizationDiagram

CPURAM ROM Disk Keyboard

Read/Write

Data bus

Address bus

Control bus

Printer/Monitor

CPU Internal OrganizationDiagram

Control Unit

ALU

Program Counter

Instruction Register

REGISTERS

Register ARegister BRegister C

Etc.

Address busControl bus signals Data bus

Control signals

Control signals

Data Values

Data values (operands)

Data values (results)

MEMORY

Memory

Types of Memory Chips

1. ROM• Read Only Memory, Not able to write to it.• Non Volatile; Retains data when power is turned-off

2. RAM• Random Access Memory, able to read and write to it.

MemoryTypes of ROM Chips• MROM (Masked Read Only Memory)

– Set by manufacturer and cannot be changed– Mostly used on consumer appliances where large quantities are produced.

• PROM (Programmable Read Only Memory)

– Programmable but only once– Programmed by blowing internal fuses– Mostly used for prototypes

MemoryTypes of ROM Chips cont.

• EPROM (Erasable & Programmable ROM)

» Totally erasable by exposing it to ultra violet light for over 20 minutes.

» Programmable outside the circuit.• EEPROM (Electrically Erasable & Programmable ROM)

» Electrically erasable. » Able to erase a portion of the memory. » Can be re programmed while in circuit.» Mostly used for computer BIOS

• FLASH Memory» Electrically erased, but it erases the entire memory.

MemoryTypes of RAM Chips• DRAM (Dynamic Random Access Memory)

» Widely used as main computer memory• SRAM (Static Random Access Memory)

» Faster than DRAM» More expensive than DRAM» Mostly used in Cache memory

• NVRAM (Non Volatile Random Access Memory)

» Does not lose data in memory when turned off.» Contains an internal Lithium battery to retain power

Memory Chip Organization

• The internal organization of ROM and RAM chips are similar.• There are two organizations

1. Linear Organization2. Two-Dimensional organization

Memory Chip Organization

• Linear Organization» It is a simpler form of organization» Used if few number of memory locations are needed

Memory Chip Internal Linear Organizationof an 8 x 2 ROM chip

3 to 8 Decoder

01

11

21

31

41

51

61

71

00

10

20

30

40

50

60

70

A2

A1

A0

E

1

0

2

4

5

3

6

7

CEOE

D1 D0

0 0 0 0

0 0 1 1

0 1 0 2

0 1 1 3

1 0 0 4

1 0 1 5

1 1 0 6

1 1 1 7

A2 A1 A0 Loc#

Memory Chip Organization

• Two-dimensional Organization» Used to manage a large number of memory

locations» Allows large memory locations using fewer chips

Memory Chip Internal two-dimensional Organization of an 8 x 2 ROM chip

2 to 4 Decoder

01

21

41

61

11

31

51

71

00

20

40

60

10

30

50

70

A2

A1

A0

E

1

0

2

3

CE

OE

D1 D0

1 to 2 Decoder

0

1E

Instruction Cycle

The Instruction Cycle

1. The Fetch cycle• Fetch an instruction from memory, then go to the

decode cycle

2. The Decode cycle• Decode the instruction – determine which

instruction has been fetched –go to execute cycle for that instruction.

3. The execute cycle• Execute the instruction, then go to fetch cycle and

fetch the next instruction.

The Instruction Cycle

• The Fetch cycle» The CPU puts an address of instruction on the address bus.» The memory decodes the address to access the desired

memory location.» The CPU allows sufficient time for the memory to decode the

address and sends a READ control signal.» The READ signal is a signal on the Control bus which the

CPU sends when it’s ready to read data from memory or I/O device.

» When the READ signal is asserted, the memory puts the instruction code to be fetched on to the data bus.

» The CPU inputs the data and stores it in one of its internal registers.

» The fetch cycle is completed.

The Instruction Cycle

• The Decode cycle» The CPU decodes the instruction.» Each instruction may require a different sequence of

operations to execute the instruction.» The CPU determines which instruction it is in order to

select the correct sequence of operation to perform.» This is done entirely within the CPU, it does not use

the system buses.

The Instruction Cycle

• The Execute cycle» The CPU executes the instruction.» The execution may be:

1. Read/write data to/from memory.2. Read/Write data to/from an I/O device.3. Perform only operations within the CPU.4. Perform some combination of the above.

Sample Diagrams

Fetch, Decode & Execute Cycles2+3=5 operation

Fetch, Decode & Execute Cycles2+3=5 operation

Fetch, Decode & Execute Cycles2+3=5 operation

Fetch, Decode & Execute Cycles2+3=5 operation

The End

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