Computer Structure and Function

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Questions and Answers

What is the primary function of the Arithmetic and Logic Unit (ALU)?

To provide storage internal to the CPU

To perform the computer's data processing functions (correct)

To sequence the logic of the computer's operation

To control the operation of the CPU and hence the computer

What is the role of the Control Unit in the CPU?

To perform data processing functions

To sequence the logic of the computer's operation

To provide storage internal to the CPU

To control the operation of the CPU and hence the computer (correct)

What is the function of the Registers in the CPU?

To provide storage internal to the CPU (correct)

To sequence the logic of the computer's operation

To control the operation of the CPU and hence the computer

To perform data processing functions

What is the purpose of the Instruction Register (IR)?

To hold the instruction loaded from memory Signup and view all the answers

What occurs during the Fetch Cycle?

The processor loads the instruction from memory Signup and view all the answers

What is the purpose of the Program Counter (PC)?

To hold the address of the next instruction to fetch Signup and view all the answers

What type of interrupt occurs when an I/O controller requests service from the processor?

I/O interrupt Signup and view all the answers

What is the purpose of the CPU interconnection?

To provide for communication among the control unit, ALU, and registers Signup and view all the answers

What is the purpose of the Memory Address Register (MAR)?

To specify the address for read and write operations Signup and view all the answers

What happens when the Interrupt Cycle is triggered?

The MBR is loaded with the saved address of the PC Signup and view all the answers

What is the purpose of the Instruction Register (IR)?

To hold the instruction after Fetch Signup and view all the answers

What is the difference between Direct and Indirect Addressing modes?

Direct Addressing specifies the address of the operand in the second part of the instruction, while Indirect Addressing uses an address of a memory word Signup and view all the answers

What is the purpose of the Program Counter (PC)?

To hold the address of the next instruction Signup and view all the answers

What happens during the Fetch Cycle?

The IR is loaded with the instruction from memory, and the PC is incremented Signup and view all the answers

What is the purpose of the Memory Buffer Register (MBR)?

To hold the data to be read or written from memory Signup and view all the answers

What is the difference between Computer Instructions and I/O Instructions?

Computer Instructions specify the address of the operand, while I/O Instructions specify the type of I/O operation Signup and view all the answers

Study Notes

Computer Structure

The computer structure consists of four main components: Main Memory, I/O devices, System BUS, and CPU
CPU consists of ALU, Internal BUS, Registers, and Control Unit
Control Unit controls the operation of the CPU and hence the computer
Arithmetic and logic unit (ALU) performs the computer's data processing functions
Registers provide storage internal to the CPU
CPU interconnection provides communication among the control unit, ALU, and registers

Creating a Program

A program is a sequence of steps
Instruction Interpreter: a device that accepts instruction codes and turns them into control signals for the arithmetic and logic hardware
Encoding Instructions: unique binary patterns identify the operation to be performed

CPU Operations

Fetch Cycle: Processor fetches an instruction from memory location pointed to by the Program Counter (PC)
PC holds the address of the next instruction to fetch
Instruction loaded into the Instruction Register (IR)
Processor interprets the instruction and performs required actions

Execution Cycle

Execute Cycle: the processor performs the required actions based on the instruction
Processor-memory: data transfer between CPU and main memory
Processor-I/O: data transfer between CPU and I/O module
Data processing: some arithmetic or logical operation on data
Control: alteration of sequence of operations, e.g., jump

Interrupts

Types of Interrupts:
- Program: "illegal instructions" (arithmetic overflow, divide by zero, or memory handling error)
- Timer: "processor can perform some time-scheduled task"
- I/O: "generated by an I/O controller to request service from the processor" (e.g., keyboard, mouse, NIC, disk drive)
- Hardware failure: "signifies some error condition with the hardware"

Instruction Cycle

Calculate Address Instruction
Instruction Fetch
Decode instruction
Calculate operand address
Fetch operand
Operand operation
Operand address calculation
Operand store
Check interrupt

I/O Modules

Transfer data back and forth with the device as if it were memory
Alternatively, the processor can grant the I/O module permission to write directly to memory - Direct Memory Access (DMA)
Interrupt occurs when DMA is complete

Registers

Program Counter (PC): holds the address of the next instruction
Memory Address Register (MAR): connected to the address bus, specific address for read and write operation
Memory Buffer Register (MBR): connected to the data bus, specific data to read or write last data
Instruction Register (IR): holds the instruction after fetch

Micro-operations

Transfer data between registers
Transfer data from register to external
Transfer data from external to register
Perform arithmetic or logical operations

Flowchart of Instruction Cycle

Fetch Cycle:
- T1: MAR <- PC
- T2: MBR <- Memory[PC]
- T3: IR <- MBR
Indirect Cycle:
- T1: MAR <- IR
- T2: MBR <- Memory
- T3: IR <- MBR
Interrupt Cycle:
- T1: MBR <- PC
- T2: MAR <- Saved Address
- T2: Memory <- MBR

Addressing Modes

Direct Addressing (MODE 0): the instruction code specifies the address of an operand
Indirect Addressing (MODE 1): the bits of the second part of the instruction designate an address of a memory word in which the address of the operand is found

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Description

This quiz covers the components of a computer system, including main memory, I/O devices, system bus, CPU, ALU, registers, and control unit. It explains their functions and how they interact with each other.