Computer Science
System Architecture
Registers
Factors impacting CPU performance
CPU
Fetch, Decode, Execute (FDE)
MDR
ACC
MAR
PC
Cache
Number of cores
Clock Speed
Memory and Storage
ROM
RAM
ROM stores the BIOS which boots the computer
ROM is non-volatile, data is stored not deleted
RAM is volatile, data is delted
RAM allows multitasking and also stores the data of the application they're running
Secondary Storage
Optical
Solid State
Magnetic
Factors for comparison
Portability
Speed
Durability
Capacity
Cost per GB
Units
Bit, Nibble, Byte, Kilobyte, Megabyte, Gigabyte, Terabyte, Petabyte
Magnetic is cheap per GB, has a high capacity, is relatively fast, is not durable as it has moving parts and not portable
Optical is cheap per GB, has a low capacity, it's not really fast, it is relatively durable but can be damaged from scratches, it's portable.
Solid state is expensive per GB, has a relatively high capacity, it's very fast, it's durable and it's portable due to its small size
Embedded Systems
Embedded systems are smaller computer systems inside a larger computer system which only has one purpose
Sat Nav, Microwave, Washing Machine
ALU
Cache
Control Unit
Computer Networks, Connections and Protocals
LAN
LAN stands for Local Area Network and it covers over a small geographical area, also the network infrastructure is typically owned by one person
WAN
WAN stands for Wide Area Network and it covers over a larger geographical area. The network infrastructure is likely owned by more than one person.
Character Sets
A character set is all the characters a computer can represent
ASCII
ASCII uses 8 bits and there's only 128 characters in in it whereas Unicode uses 16 or 32 bits and there's 65336 possible characters (16 bits) or 4 billion possible characters (32 bits)
Images
An image is a grid of pixels, each pixel represents a colour and each colour is stored in binary
Metadata is information about the image e.g. width, height, colour depth
Stores the address of the next instruction
Stores the address of the instruction that's about to be fetched
Stores the data that has been fetched
Stores the results of the calculations
Sound
Sound is sampled at regular intervals. The amplitude of the wave is measured and then the sample is stored as binary.
Client Server
Peer to Peer
Computers are networked to each other without a central server
Relationship between two computers in which one, the client, makes a service request from another server
Low cost and easy to set up
Updates can only be done separately and PC has to be on to access
Expensive, hard to set up, requires more hardware
Secure, can be backed up, files can be accessed anywhere
DNS
The URL is sent from your browser to the DNS server. The DNS server then returns the IP address of that website to your web browser. Your browser uses that IP address to access that website, the website then provides the data accessed however if the first DNS server cannot retrieve the IP address, the domain name is sent to higher level DNS.
The value in PC is copied to the MAR, data and instructions are fetched from main memory using the address in the MAR and stored in the MDR. The PC is incremented. The MDR is decoded and the instruction is carried out and the cycle is repeated.
Star & Mesh Topologies
Star: Very few data collisions and it's secure.
It can be expensive and may require expertise.
Mesh: Devices can join with no effect and there's no single point of failure.
It can be expensive as it requires a large amount of wiring.