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Components of a Computer System Cheat Sheet (DRAFT) by

This is a draft cheat sheet. It is a work in progress and is not finished yet.


Key Word
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
Very fast memory but slower than registers, holds regularly used data
Memory Location than tempor­arily holds data
PC: Program Counter
Holds the location of the next instru­ctions
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
Copy memory address from the PC to the MAR, copy the instru­ction in the MAR to the MDR and increase the PC
The instru­ction in the MDR is decoded by the CU. It will then prepare for the next step
The instru­ction is performed, usually by the ALU

System Perfor­mance

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

Von Neumann Archit­ecture


Primary and Secondary Storage

Key Word
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
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