4.7.3 Structure and Role of the Processor and all its Components

Central Processing Unit (CPU)

the overall brain of a computer that executes instructions to run programs

Arithmetic Logic Unit(ALU)

part of the CPU that performs all the arithmetic and logic operations

Control Unit (CU)

part of the CPU that manages CPU activities and co-ordinates the fetch-execute cycle

Registers

they are small high-speed storage locations for temporary data during processing.

Program Counter (PC)

a type of register that holds the memory address of the next instruction to execute

Current Instruction Register (CIR)

a type of register that stores the instruction currently being executed

Memory Address Register (MAR)

a type of register that contains the memory address of the location to be read from from or written to

Memory Data Register (MDR)

a type of register that holds the data read from or written to memory

Status Register (SR)

a type of register that holds status bits that indicate system states, such as interrupts

Clock

part of the CPU that generates timing signals at a regular frequency allowing for instructions to be processed

CPU Buses

they are communication channels between the CPU and other PC components

The Fetch-Execute Cycle

a continuous process the CPU uses to execute instructions.

The Fetch Stage

a stage of the fetch-execute cycle where the instruction from memory is retrieved

The Decode Stage

part of the fetch-execute-cycle where the retrieved instruction is converted to binary

The Execute Stage

part of the fetch-execute cycle where the decoded instruction is carried out

The Instruction Set

defines all operations a processor can perform and are stored in machine code

Opcode

this specifies the action to be performed on the operands

Operands

data or memory location that the opcode is performed on

Immediate Addressing

the type of addressing where the operand contains the actual value

Direct Addressing

the type of addressing where the operand specifies a memory address

Logical Shift

this is a binary operation that shifts all bit either left or right

Interrupts

a signal where another part of the computer is requesting the attention of the CPU

Detection of an Interrupt

this is the process where the control unit identifies the changes in the status register during the fetch-execute cycle

Handling of an Interrupt

this is the process where the CPU halts its current task, saves the volatile environment and executes an Interrupt Service Routine to process the interrupt

Vectored Interrupt Method

this is where the ISR is specific to the type of interrupt

Cores

a part of the CPU which can independently run its own fetch-execute cycle

Cache

small high-speed memory built into the CPU that stores frequently used data to reduce access

Clock Speed

this factor determines the number of cycles per second measured in GHz

Word Length

this is the number of bits processed by the CPU as a single unit

Address Bus width

this type of bus width determines the range of memory addresses the CPU can access

Data Bus Width

this type of bus width determines how much data can be transferred in one cycle

Von Neuman Architecture

this CPU architecture uses a single memory for instructions and data which can cause a bottleneck; used in most traditional computers

Harvard Architecture

this CPU architecture separates memory for instructions and data improving speed; mostly used in embedded systems and DSPs