A02

 Fetch, Execution, and Input/Output

The central processing unit (CPU) is the heart of the computer.

Data is stored in bits.

- One byte is equal to eight bits.

- A bit is the smallest unit of data measurement.

- It can be either 0 or 1.

- Computers interpret our intentions and process information by converting data into binary forms.

Functional Units

Primary Memory:

- Also known as the main memory.

- Organized into words of typically 32 bits.

- 32 bits contain four 8-bit bytes.

- Programs and their data must be stored in this memory to be executed.

Cache Memory:

- An adjunct to the main memory, fabricated on the processor chip.

- It is smaller and faster memory.

Processor:

- Consists of logic circuits, timing and control circuits, and registers.

Arithmetic and Logic Unit (ALU):

- Most computer operations are executed in the ALU of the processor.

- It performs arithmetic or logic operations.

Control Unit:

- Coordinates the operations of the memory, ALU, and I/O to store and process information.

Computer:

- Accepts information in the form of programs and data through an input unit and stores it in memory.

- The information is fetched under program control into an ALU where it is processed.

- The processed information leaves the computer through an output unit.

- All these operations are directed by the control unit.

Instruction Cycle:

- The computer system can run very complex programs, but its basic operation is simple.

- It repeats basic operations billions of times per second.

- A single cycle of operation is called the instruction cycle.

Instructions and Programs:

- An instruction specifies an operation and the locations of its data operands.

- A 32-bit word holds one encoded instruction.

- A sequence of instructions executed one after another constitutes a program.

- Both the program and its data are stored in the main memory.

Instruction Types:

- Load

- Store

- Operate

Processor Components:

- The program counter register holds the memory address of the instruction.

- The instruction register holds the current instructions.

- General-purpose registers hold data and addresses.

- Control circuits and the arithmetic and logic unit (ALU) fetch and execute instructions.

Program Counter (PC):

- As each instruction is fetched, the program counter increases its stored value by 1.

- After each instruction is fetched, the program counter points to the next instruction in the sequence.

- When the computer restarts or is reset, the program counter normally reverts to 0.

Handling I/O Devices:

An application program can:

- Read data from an input device.

- Write data to an output display screen.

- Sense the readiness of an input or output (I/O) device to perform a transfer.

Performance

How quickly can a program be executed?

Factors include:

- Speed of the electronic circuits in the processor.

- Access time to the cache and the main memory.

- Design of the instruction set.

- Number of operations that can be done at the same time.

Technology:

Improvements in transistor materials allow for faster execution of instructions.

Performance - Parallelism

Multicore Processors (across multiple cores):

- Multiple processing units can be fabricated on a single chip.

- Each of these processors is called a core.

- The term processor is used for a complete chip.

- There are various processors for chips, such as dual-core, quad-core, and octo-core.