Central Processing Unit (CPU)

• The central processing unit (CPU) is the hardware device in a computer responsible for processing.
• CPUs in Von Neumann architecture connect to memory (RAM) and I/O devices via a bus.
• When a computer starts, the CPU fetches instructions from main memory, executes them, and repeats until powered off.

Fetch-Decode-Execute Cycle

• The CPU fetches an instruction from memory using the address bus and control bus.
• The control unit decodes the instruction and signals other CPU parts on what to do.
• The CPU then executes the instruction completing the function.

Key CPU Components

• The arithmetic/logic unit (ALU) performs calculations and logic operations.
• Registers are very fast memory locations inside the CPU which hold instructions, addresses, or data.
• The control unit organizes actions of the CPU components.
• An electronic clock synchronizes the cycle, with clock speed (GHz) indicating cycles per second, thus faster processing.
• Faster clock speeds increase heat production and power consumption.

Bus System

• The bus connects the CPU to other devices using address, data, and control buses.
• The address bus carries memory addresses.
• The data bus carries data being read or written.
• The control bus carries control signals.
• Bus width determines the amount of data communicated at once.

RAM (Random-Access Memory)

• RAM is a temporary store for data and instructions.
• "Writing" saves data to memory with specified data and addresses.
• "Reading" retrieves data using a memory address.
• Data and instructions are stored as binary numbers in bytes.

Cache Memory

• Cache memory is a small, fast memory between the CPU and RAM
• Code or data is loaded from RAM into the cache for faster access.
• Modern CPUs have separate instruction and data caches.
• Cache is organized in levels (L1, L2, L3), with L1 being the fastest and smallest, located on the processor core.
• Multicore processors typically have dedicated L1 and L2 caches per core, and a shared L3 cache.

Multicore Processors

• Modern CPUs often have multiple processor cores.
• Common configurations include dual-core (2), quad-core (4), octa-core (8), and deca-core (10).
• Multicore processors enable parallel processing or multitasking.

Factors Affecting CPU Performance

• Clock speed, number of processor cores, and cache size influence CPU performance.
• A bottleneck occurs when a slow component slows down the entire system.
• Cache memory helps solve the bottleneck problem.

ROM (Read-Only Memory)

• ROM is non-volatile memory, retaining data without power.
• ROM stores the initial program (BIOS/UEFI) that runs when a computer starts.
• Programs permanently stored in ROM are called firmware.

Virtual Memory

• Virtual memory uses a portion of the hard disk as RAM when RAM is full.
• Data is swapped between RAM and virtual memory as needed.
• Accessing virtual memory is slower than RAM, which can lead to disk thrashing if overused.