Processors: ALU, CU, and the FDE Cycle

Study Notes

Processors: ALU, CU, Registers, and Buses

A processor, the "brain" of a computer, performs calculations and manages data.
The Arithmetic Logic Unit (ALU) performs arithmetic and logical operations.
The Control Unit (CU) fetches instructions, decodes them, and controls the execution of operations.
Registers are high-speed storage locations within the processor holding data.
- Examples include general-purpose registers and special-purpose registers like the program counter and accumulator.
Buses are communication pathways connecting different components.
- Data buses transfer data, address buses specify memory locations, and control buses send control signals.
- These buses enable flow of information between components.

Fetch-Decode-Execute (FDE) Cycle

The FDE cycle is the fundamental process a processor uses to execute instructions.
Fetch: The CU fetches the next instruction from memory.
- Instruction's address is in the program counter.
Decode: The instruction is broken down into smaller parts to understand what operations to perform.
Execute: The ALU performs the necessary operations.
- Data is retrieved from registers or memory, and the result is stored in a register or memory.

CPU Performance

CPU performance is measured by various factors.
- Clock speed (in GHz) which is the frequency at which the processor's internal clock ticks.
- Number of cores (multi-core processors can process multiple instructions concurrently).
- Cache memory (higher cache capacity can reduce read times from RAM).
- Instruction set architecture (ISA): the instructions a CPU understands. Complex Instruction Set Computer (CISC) vs Reduced Instruction Set Computer (RISC).
- Instruction pipeline depth (number of stages).
Higher clock speed, more cores, and larger cache typically improve performance.
CPU, memory, and I/O speed interact to impact overall system speed.

Pipelining

Pipelining is a technique used to improve the performance of a processor.
It overlaps stages of the instruction cycle which allows different instructions to be processed concurrently.
A pipeline consists of several stages that execute in sequence.
- An instruction might be in a different stage of execution than another instruction.
Improved throughput, but latency may increase due to longer instruction flow length and potentially more complex circuitry.

Computer Architecture

Architecture defines the logical structure of a computer system.
Different architectures exist, each with various design choices.
Underlying components and operations are determined by the architecture.
Important design considerations include instruction complexity, parallelism and memory access.
Examples:
- Von Neumann architecture is the traditional way memory and instructions reside in the same address space.
- Harvard architecture separates the memory spaces for instructions and data.
Various factors affect architectural choices, including cost, performance, and design constraints.

Description

This quiz explores the essential components of a processor, including the Arithmetic Logic Unit (ALU), Control Unit (CU), registers, and buses. It also covers the Fetch-Decode-Execute (FDE) cycle, which is fundamental to instruction execution in processors. Test your knowledge on how these elements work together to make computing possible.