The Central Processing Unit (CPU) & Primary Memory

The Central Processing Unit (CPU), housed on the motherboard as a microprocessor, interprets and executes all software instructions, performs calculations, and coordinates all peripheral hardware components. • The Three Fundamental Internal Sub-Units of the CPU: 1. The Arithmetic and Logic Unit (ALU): - The computational powerhouse of the processor. - Arithmetic Operations: Executes mathematical calculations: Addition (+), Subtraction (-), Multiplication (*), and Division (/), - Logic Operations: Evaluates logical conditions and comparisons: Equal to (=), Greater than (>), Less than (<), NOT EQUAL TO, AND, OR. 2. The Control Unit (CU): - The master manager or supervisor of the entire computer system. - It extracts instructions from memory, decodes what actions are required, generates timing and control pulses, and directs the ALU, registers, and I/O devices. 3. Registers: - Extremely high-speed, tiny internal temporary storage cells inside the CPU chip itself. - Hold active data, immediate operands, current instructions, and memory addresses during execution (e.g. Program Counter, Instruction Register, Accumulator).

Every single instruction processed by the CPU is executed through a continuous four-step cycle known as the Machine Cycle: 1. FETCH: The Control Unit retrieves the next instruction from the system RAM and places it into an internal CPU register. 2. DECODE: The Control Unit translates the fetched instruction into binary electronic signals and determines what operations must be carried out. 3. EXECUTE: The Arithmetic and Logic Unit (ALU) performs the designated mathematical computation or logical comparison. 4. STORE (Writeback): The result generated by the execution step is written back to an internal register or system memory (RAM) for later display or storage. • CPU Clock Speed: The speed of the machine cycle is regulated by an internal quartz crystal clock. Measured in Gigahertz (GHz)—a 3.2 GHz processor executes 3.2 billion machine cycles every second!

Primary memory (main memory) communicates directly with the CPU via high-speed buses: • 1. RAM (Random Access Memory): - Volatile (Temporary): Its contents evaporate and are completely lost when electrical power is switched off. - Read and Write Memory: The CPU can both read data from RAM and write new data into RAM effortlessly. - Function: Acts as the immediate working desk for the computer, holding the active operating system kernel, open programs, and unsaved work. - Capacity: Measured in Gigabytes (e.g. 4 GB, 8 GB, 16 GB). • 2. ROM (Read-Only Memory): - Non-Volatile (Permanent): Retains its contents indefinitely even when the computer is completely unplugged. - Read Only: Data is permanently written during manufacturing and cannot be modified by ordinary users. - Function: Holds the computer's firmware—the BIOS (Basic Input/Output System) and the bootstrap loader instructions that wake up hardware when turned on. - Capacity: Typically small (a few Megabytes).

• Cache Memory: - An ultra-fast buffer of static RAM (SRAM) built directly onto the CPU chip itself (L1, L2, L3 cache). - Operating Speed: Much faster than regular RAM. - Purpose: Stores frequently used instructions and data so the ultra-fast CPU does not have to wait for slower system RAM. • The System Bus: A collection of parallel high-speed copper traces connecting the CPU to memory and peripherals: - Data Bus: Carries the actual binary data between CPU and memory. - Address Bus: Carries the physical memory address where data is located. - Control Bus: Transmits synchronization, read, and write command signals.