Computing A451: Topic 2 Computer Hardware

Computing A451: Topic 2 Computer Hardware

1. CPU - Central Processing Unit

   • Carries out the processes of a computer
     • Fetch-Decode-Execute Cycle
   • Made up of Cores
     • ALU - Arithmatic Logic Unit
       • Does the calculations in a computer
       • Gives out the instructions of the CPU
     • CU - Command Unit
       • Controls what data flows through the CPU
     • Level 1 Cache
       • To store data which is about to be or has just been used
     • Quad-Core processors contain four cores
     • Doubling the ammount of cores doesn't double your computers speed
     • If you have more than one core they need to be able to work with each other
     • How fast they work is dependant on the clock speed
       • When the clock speed is increased this is known as overclocking
         • Lowers the reliability of the computer
         • Used when making gaming computers
         • Consumes more power
         • Overheats
         • This is done in the computers BIOS
       • Measured in mHz or gHz
         • One cycle per second is 1 Hertz
         • 1 gHz carries out 1 billion cycles per second
   • Two types of CPU
     • RISC
       • RISC CPU's have less instructions compared to CISC CPUs
       • Has to combine simple operations to carry out more complicated ones
       • Small
     • CISC
       • CISC has hundreds of instructions
         • Including complex instructions but is less effective at carrying out simpler tasks
       • Big

2. Storage

   • RAM -Random Access Memory
     • Volatile
       • Loses its memory after the power is cut
     • The OS which is stored in ROM is loading into RAM when you turn on your computer
     • Empty when you turn the computer on
     • Known as main memory
       • Stores modules for your applications to work
     • RAM allows you to have multiple windows open at once
     • Two types of RAM
       • Dynamic RAM
         • Used for the main memory
         • Must be constantly refreshed
       • Static RAM
         • Complex and expensive
         • Must be constantly refreshed
           • An example can be Cache
             • 3 Levels of Cache
               • Level 1 is inside the CPU
               • Levels 2 and 3 are outside the CPU
         • Access times are faster than Dynamic RAM
       • If there isn't enough space in RAM the data will be moved to Virtual Memory
         • Virtual Memory has much slower access times.
           • Latency increases
         • Virtual memory is a part of the Hard Disk which is reserved for when RAM is low on memory
           • Time is taken up moving data around rather then executing instructions
         • When RAM is clear the data in Virtual Memory will be moved into RAM
           • Easier to access compared to RAM but longer time to write to
         • Your computer will alert you when you are using Virtual Memory
   • ROM - Read Only Memory
     • Files which are stored on ROM cannot be edited or copied.
       • Films or Music CDs use this file type
       • Also stores the Computer BIOS
         • The BIOS is the startup instructions for a computer
           • Basic Input Output System
     • Primary data which retains data without power
       • Non-volatile
     • Two types of ROM
       • PROM
         • Programmable Read Only Memory
         • Cheap
         • Programmed directly by a programmer
           • Not re-programmable
           • Only programmed once
       • EEPROM
         • Electronically Erasable Programmable Read Only Memory
         • Popular in PCs and Smartphones
           • Easily updated by a manufacturer
         • Similar to a rewritable CD
   • Access Times
     • The time that is takes to access a file is called latency
       • This can take milliseconds for a computer to execute a file and access the memory
   • Secondary Storage
     • Optical Disk
       • Advantages
         • Lightweight Media
           • Easy to carry
         • Easy to write to
         • Used to transfer files from one location to another
       • Disadvantages
         • Easily Scratched
           • Lose Memory
     • Magnetic Hard Disk
       • Advantages
         • Can store large amounts of data
         • Can be written to
         • Quick to access
       • Disadvantages
         • Cannot be easily transfered
         • They will eventually fail

3. Binary Logic

   • Binary is a number system consisting of the numbers 1 and 0
     • Binary is used by the computer and is used to represent analogue data into digital data
     • This is the only language that a computer system can understand
     • The numbers 1 and 0 are also called a state
       • These states are known as ON and OFF
         • They are determined by the state of the current switch, ON being 1 and OFF being 0
           • There are three types of switches known as 'Gates'
             • Each gate outputs a signl depending on what state had entered the gate
               • AND Gate
                 • For an AND gate to output the state 1 both of the states entering the gate must be the state of 1
               • OR Gate
                 • For an OR gate to output the state 1 at least one of the two states entering the switch must be the number 1
               • NOT Gate
                 • For a NOT gate to output the state 1 the only state entering the gate must be the state of 0
                 • A NOT gate flips the state of the switch
               • One gate can be connected to another which creates a complex system which the computer uses to run.
             • Each gate has it's own symbol and table to work out what the output at each gate will be
               • These are helpful when trying to work out more complex gates