Notes regarding computer systems for gcses and a level. Detailed explanation of the most important topic for Computer systems. Helps with homework and better exam results.
Written by a previous student, so included only the most essential material.
BIOS stands for Basic Input output system. All it does is check at the start of the computer to
see any essential devices like RAM, HDD. SDD, Keyboard, Mouse etc. are working before
getting into OS
Communication between devices via interfaces.
DEDICATED SYSTEM: system dedicated to do one specific task. E.g. controlling robotic
arm in factory, air traffic control system, check out till system
EMBEDDED SYSTEM: system that is built in the machine and user have to follow the
programmer's intention. They cannot change any programming. E.g. washing machine,
microwave, DVD player
GENERAL PURPOSE SYSTEM: System that allows the user to do anything they want. E.g.
computer, tablet, smart phone
Central Processing Unit
John von Neumann
CPU = Brain of the computer (Processor) + Main memory (RAM)
- Processor is divided into ALU and CU
- Memory is divided into RAM, Cache and register
Store memory addresses.
, CPU parts
The purpose of the CPU is to fetch the instruction, decode it and then it will execute the
instruction.
It consists of the following components.
- ALU performs calculations and logical decisions.
- CU sends signals to control how data moves around the CPU. It manages timing of
the data flow.
- Cache provides fast access to frequently used instruction and data
- Register is a small and fast memory that holds data
Registers (KB) and Cache (MB) are built within the Processor which means they are the
most expensive and smallest in size but also mean the fastest to fetch instruction and store
data.
RAM (GB) and Hard Disk (TB) are separated parts and outside of the processor. They are
cheaper and come in large capacities but very slow performance.
Register
- Register has 4 different types (PC, MAR, MDR and ACC)
- Program Counter holds the address of the next instruction in memory
- Memory Address Register holds the address of where data is to be fetched or
stored
- Memory Data Register holds the data fetched from to be written to the memory
- Accumulator holds the results of calculations
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