Computer Basics

Central Processing Unit(CPU)

CPU (Central processing unit) executes the instructions given by a computer program. It performs the following operations
• Arithmetic operations
• Logical operations
• Input/Output operations

Parts of CPU:
• Arithmetic Logical Unit (ALU) do the arithmetic and logical operations.
• Registers are used for accessing and storing data required.
• The Memory address register (MAR) has the address of memory location to be accessed.
• The Memory data register (MDR) has the data which is read from the location which MAR has.
• The Instruction Register (IR) has the instruction to be executed
• The Program Counter (PC) has the address of the memory location for next instruction

• The cache memory temporarily holds the instructions and data required by CPU. It thus helps in processing fast as it saves the time of loading from RAM. The Level 1 cache which is closest to CPU has the instruction cache (L1i) and the data cache (L1d). Level 2 and 3 caches has the instruction and data that are needed next
• The accumulator stores result of the operation of ALU
• The process of fetching instructions (locations of data and the data itself), decoding the instruction and executing the instruction is called CPU instruction cycle.
• The CPU instruction cycle is managed by the control unit
• The CPU instruction cycle is synchronized by the CPU clock

Buses:
• The data and signals between the processor and other components are sent by buses
• The address bus carries memory addresses from the processor to other components
• The data bus carries the data from the processor to other components
• The control bus carries the control signals from the processor to other components

Types of CPU:
• Single-core CPU
 Can execute one command at a time
 Not good for multi-tasking
• Dual-core CPU
 Acts like 2 CPUs
 Can execute more than one command at a time
 Multi-tasking is possible

• Quad-core CPU
 4 cores working simultaneously
 More multi-tasking capabilities than dual-core CPU
• Similarly hexa-core, octa-core and deca-core CPUs are powerful than Quad-core

History of CPU:
• Vacuum tubes – First Generation – 1940s and 1950s
• Transistors – Second Generation – 1950s and 1960s
• Integrated Circuits (Ics) – Third Generation – 1960s and 1970s
• Microprocessors – Fourth Generation – 1970s to Present
• Artificial Intelligence – Fifth Generation – Present and Future

CPU performance depends on many factors. The instructions per second of CPU depends on the rate of the clock measured in hertz and instructions per clock. The processing capacity of the computer increases if multiple processors (cores) are plugged into an integrated circuit (IC). As the number of cores increases, the performance of the computer increases.