Components of a Computer System Cheat Sheet

Key Word	Description
CPU: Central Processing Unit	Brain of the computer, processes all data
CU: Control Unit	Executes program instructions, overall control of the CPU, holds PC
ALU: Arithmetic Logic Unit	Carries out calculations on data, contains the accumulator
Cache	Very fast memory but slower than registers, holds regularly used data
Registers	Memory Location than temporarily holds data
PC: Program Counter	Holds the location of the next instructions
Accumulator	Stores result of calculations from the ALU
MAR: Memory Address Register	Holds the memory address about to be used, from the address bus
MDR: Memory Data Register	Holds the actual data which has been used or is about to be used, from the data bus
CIR: Current Instruction Register	Instructions from the MDR are opened here
Address Bus	Carries addresses from the CPU to the RAM or the I/O Devices, it only goes one way
Data Bus	Carries data from the RAM to the CPU and goes two directions
Control Bus	Control signals are sent across
Fetch	Copy memory address from the PC to the MAR, copy the instruction in the MAR to the MDR and increase the PC
Decode	The instruction in the MDR is decoded by the CU. It will then prepare for the next step
Execute	The instruction is performed, usually by the ALU

Clock Speed	The number of instructions a single core can carry out per second (Hz) The higher the clock speed, the faster the computer
Number of Cores	You can independently process data. More cores means more instructions processed at a time
Disadvantages of Cores	Not all programs allow many cores to process data
Disadvantages of Cores	Not all programs allow many cores to process data
Cache Size	A larger cache means the CPU will be faster because it is easier for data to be accessed than it being in the RAM
More RAM	The more RAM, the more applications a CPU can smoothly run, making it faster

Key Word	Description
RAM: Random Access Memory, Main Memory	It can be read or written It is temporary All files are stored here when in use Slower than cache faster than secondary storage
ROM: Read-Only Memory	Non-volatile memory Contains instructions for a computer to boot up (BIOS)
BIOS: Basic Input Output System	Instructions in the ROM that a computer needs to boot up
Virtual Memory	When the RAM is full, a space on the HDD to store data that currently not in use.
Disadvantages of Virtual Memory	Disk Thrashing Very slow compared to RAM The HDD is not geared to changing data frequently
Secondary Storage	Where files we want to keep is stored, mainly when it is not in use
SSD: Solid State Disk	No moving parts- fastest, quickest, reliable, durable Made from microchips and electrons pass through High Capacity
Examples of SSD	SD Card, USB Stick, SSD
Optical Disk	Laser Light burns marks unto a disk Cheap, low capacity, Old-fashioned, Portable Not durable as easily scratched
Examples of Optical Disk	CD-ROM, DVD-ROM, Blu-Ray
Magnetic Tape	Patterns of magnetism to read data Noisy due to moving parts Not very reliable, durable, highest capacity and fast
Examples of Magnetic Tape	Hard Disk Drive, Floppy Disk, Magnetic Tape
HDD: Hard Disk Drive	High Capacity, Reliable Between 5400 and 15000rpm Backing up and transporting data

Components of a Computer System Cheat Sheet (DRAFT) by gloryo