Computer Architecture Fundamentals: CPU, Memory, Buses, and Addressing

Core Computer Architecture Components

CPU Registers Explained

CPU registers are small, high-speed storage locations within the central processing unit (CPU) that hold data and instructions for immediate processing.

Accumulator Register

The Accumulator Register stores the results of executed operations. It connects to input registers for feedback in chained operations and also connects to the data bus for sending results to main memory or the control unit.

Program Counter (PC)

The Program Counter (PC) stores the memory address of the next instruction to be executed.

Instruction Register (IR)

The Instruction Register (IR) contains the instruction currently being executed.

Understanding Computer Buses

A bus is a channel or set of parallel connections that links two or more computer devices, facilitating communication between them.

• Data Bus

  The Data Bus is used for data transmission between components.

• Address Bus

  The Address Bus is used to transmit memory addresses for data access.

• Control Bus

  The Control Bus transmits control signals to manage access of various devices to the buses and to coordinate operations within microcomputers.

Main Memory & Associated Registers

Main Memory Function

Main Memory is the component responsible for storing information for access. It generally stores programs and data that the CPU needs to access quickly.

Memory Data Register (MDR)

The Memory Data Register (MDR) contains the data to be written to memory or the data read from memory.

Memory Address Register (MAR)

The Memory Address Register (MAR) holds the memory address of the cell where a read or write operation is to be performed.

Machine Language Addressing Modes

When coding in machine language, different addressing modes determine how the operand (the data or the address of the data) is specified within an instruction.

Immediate Addressing

In Immediate Addressing, the operand value is directly included within the instruction itself.

Direct Addressing

In Direct Addressing, the operand field directly specifies the memory address where the data is located.

Indirect Addressing

In Indirect Addressing, the address specified in the instruction is not the data itself, but rather the address of another memory location where the actual data resides.

Relative Addressing

In Relative Addressing, the effective address is calculated by adding an index value (displacement), typically found in a CPU register, to the base address specified in the instruction.

Memory Access Methods

Sequential Access

In Sequential Access, the access time to a memory location depends on its physical position or address within the memory.

Direct (Random) Access

In Direct (Random) Access, the access time to any memory location is uniform, regardless of its physical position.

Cache Memory Fundamentals

Cache Memory is a small, high-speed memory located between the main memory and the processor. It stores frequently accessed data and instructions to reduce access times to slower main memory.