Computing

• manages the execution of instructions
• fetches instruction, decodes it then synchronises its execution
• sends contol signals to other parts of the computer
• uses a contol bus

• stores OS
• stores data currently in use
• stores software and the boot pragram

• carries out arithmetic instructions
• carries out logical instructions
• acts as a gateway to the processor

• checks on where the next instruction is in the memory
• tell the processor where the next instruction is

• where the address that was read from the PC is sent
• stores address here

a copy of an instruction, that was in the address, is placed here

• the instruction is copied here
• instruction is split into its parts

carry out the task

carries data being transmitted

carries identification about where the data is being sent/ coming from

carries control signals from the control unit to allow synchronisation of signals/commands to the processor

• data that is held on here cannot be altered
• data is not erased when power is switched off
• non-volatile
• e.g. boot program

• data is wiped clear when the power is switched off
• volatile
• e.g. applications software

• Hardrive: consists of a series of disks (platter), increases volume of data, speed of access, divisions on surface of disks, format disk
• Magnetic tape: archiving files, old device, data stored linearly, access time is slow

• CD's and DVD's: RW
• surface divided into sectors and has a single track
• indentations

• flash memory or USB stick
• no moving parts
• data is stored in a thin layer of oxide between non-conductive layers

• uses a laser beam to read the code
• Advantages: fast, reliable, check digit makes it good at rejecting errors
• Disadvantages: input limited to numbers
• Uses: identification of packages, tills in shops

• magnetic ink character recognition
• uses a special ink and reads number when passes through the MICR
• Advantages: high level of security, automation
• Disadvantages: expensive system, accept a few characters
• Uses: cheques

• converts a scanned image of text into an actual text file by recognising each character
• Advantages: converts large amounts of text, can edit text
• Disadvantages: poor recognition

• uses IR light to scan marks on prepared forms
• Advantages: quick and reliable
• Disadvantages: has to be simple data capture forms, cannot be used for text and number input
• Uses: multiple choice tests, lottery tickets

• uses reflected light to read from a paper document
• Advantages: scanned image can be enhanced
• Disadvantages: loss in quality, lots of memory space

• dot matrix
• inkjet
• laser

• prints by moving a pen sideways over the surface of a sheet of paper
• Advantages: accurate, produce larger printouts
• Disadvantages: slow, expensive, cannot print photographic images

• converts an alternating electrical current into sound
• Advantages: cheap, high quality sound
• Disadvantages: digital sound signal has to be converted

• digital sound saved for playback
• voice recognition
• Advantages: convert voice into text
• Disadvantages: take up alot of memory

• detects changes in physical or chemical environment and converts them into electrical signals
• Advantages: huge range of possible sensors
• Disadvantages: need an interface to convert analogue signals

• used to control physical movement
• Advantages: easily controled, faults easy to diagnose
• Disadvantages: expensive, complicated

• Buffers
• Interrupts
• Data is sent to the buffer from the primary memory
• An interrupt is sent once the buffer is full
• Buffer is emptied to storage device
• Once the buffer is empty an interrupt is sent to the processor to request buffer refill