Computer Systems

Computer Systems

1. System Architechture

   • CPU
     • Carries out the instructions for the FDE cycle
     • ALU: Performs logical and Arithmetic calculations
     • CU: Provides timing and control signals
     • Cache: to store instructions that are going to be reused
     • Factors that effect the CPU
       • Clock speed
       • Cache sze
       • Number of cores
     • MAR: Holds the memory address of the data that needs to be accessed
   • FDE Cycle
     • Fetch-decode-execute cycle
       • MDR: Holds actual data or instructions
       • Accumulator: Stores the immediate result of a calculation
       • PC: Holds the address of the next instruction in the cycle
     • Fetch
       • 1. Copies memory address from the PC to the MAR.
       • 3. Increases the PC to the point of the address of the next instruction
       • 2. copies the instruction in the MAR to the MDR
     • Decode
       • The MDR instructions are decoded by the CPU
     • Execute
       • The instruction is performed
   • Embedded System
     • To perform a single task from within a larger piece of equipment
     • Washing machines, dishwashers, cameras and printers

2. Memory

   • RAM
     • Random Access Memory
     • Volatile
     • Stores all data that is currently being used
     • Slower than the CPU cache
     • Faster than the Secondary storage
   • Virtual Memory
     • Opened when the RAM is full
     • A.K.A: Secondary storage
     • Can make the computer slower
   • ROM
     • Holds the BIOS
     • Read only
     • Non-volatile
     • Uses Flash Memory
       • Stores data in electrical circuits
       • Used in SD cards, USB sticks and SSD'S

3. Storage

   • Secondary Storage
     • Non-volatile
     • Read/write speed is slower than primary storage
     • Magnetic Hard disks
       • internal storages for PC and laptops much cheaper HDD have high data storage amount long lasting and reliable can be damaged by large impacts
     • Solid State Drives
       • no moving parts faster read/write speed than HDD used for the same thing as HDD portable
     • Optic Disks
       • 3 forms:Read-only, Write-once, Rewriteable.CD - 700 MBDVD - 4.7 GBBlue-ray - 25 GBuse is declining: streaming services availiable, phones and tablets don't have optic disk drives. Cheaper per GB, portable, no damage by water but do scratch easily.
     • Magnetic Tape
       • used for archiving. greater storage capacity lowest cost per GB need a specialized device to read/write. very slow when finding data fast read/write speed when data is found.

4. Networks

   • LAN
     • Local Area Network one location network e.g. a house
   • WAN
     • Wide area network made of lots of LANs e.g. the internet, businesses with multiple offices
   • Factors affecting the performance of networks
     • Bandwidth Choice of hardware and network topology
   • Client-server
     • files and software stored in one place on the server server stores important data such as passwords, usernames, and access information Advantages: easy to keep track of files easy to perform backups easy to install and update sotware easy to manage network security servers are always on disadvantages: expensive and needs an IT specialist to maintain it if the server goes down all data is lost server may not wor if to many clients are using the server
   • Peer-to-Peer
     • Don't use servers files are stored on the individual device advantages: Easy to maintain if one device goes down the rest aren't affected Disadvantages: no centralised management easy to loose trak of where a file is stored machines are less reliable prone to slow down
   • Hardware
     • NIC
       • Network interface controller allows the device to connect to a network for both wired and wireless connections
     • Switches
       • Connect devices to a LAN recieves data and transmits the data to the the device on the network with the correct MAC address
     • Routers
       • Transmits data between networks always connected to 2 different networks connects a LAN to the internet direct data on the internet
     • Cables
       • CAT 5e/6 : 4 twisted pairs of copper cables twisted together to avoid interference used for Ethernet Coaxial: made from a single copper wire surrounded by plastic for insulation as well as a metal mesh which reduces interference. Fibre Optic: data is transmitted as light very expensive don't suffer from interference can transmit over large distances without loosing signal quality 
   • Wireless network
     • Uses radio waves to transmit data you need a wireless access point to do this  
     • WI-FI
       • Uses radio frequency bands 2.4 GHz and 5GHz bands are split into channels the channels in the 2.4 GHz band overlap performance is effected by interference Advantages of: 2.4GHz: greater range goes through solid walls easier 5GHz: faster over short distances less chance of interference
   • The internet
     • DNS
     • Hosting
     • The Cloud
   • Virtual Networks
     • Entirely software based multiple virtual networks can be on the same physical network virtual networks have their own security

5. Network topologies