The Central Processing Unit (CPU)
Computer hardware is physical part of computer
Purpose of CPU : processes data including sorting/searching data, performing calculations, logical decision-making, synchronising data on different devices, control of input/output storage devices
Computer system runs program. When program run, loaded into main memory (RAM).
Each program instruction processed by CPU as fetching, decoding and then executing the instruction.
This process is then repeated. Many possible instructions e.g locating/loading/calculating data
CPU is mounted on motherboard and controls storage devices & input/output of data
CPU performance affected by factors: Clock Speed, Number of Cores, Cache - Memory Type, Cache - Disk Type
Clock speed controls process of executing instruction, Cores allow instructions to be performed in parallel, 'Memory' stores data faster than RAM, 'Disk' stores regularly used data
Electronic devices in computer hardware have two states ON and OFF. Represented by 1 and 0
Binary stored in system as different voltage levels, 0 low 1 high. Electronic circuits used can be wired together to form logic calculations. Circuits are based on logic gates.
NOT gate where output is opposite of the input. Looks like a triangle.
OR gate 0 when all inputs are 0 but 1 when any input is 1.
AND gate is 1 when all inputs are 1. 0 is when any inputs are 0. Symbol is stretched D
Logic gates combnined to form logic circuits
Boolean expressions are used in computer programs - give boolean logic output of true or false
Logic diagrams can be drawn from boolean expre4ssions
eg R = (A OR B) AND (NOT C)
Primary storage devices knownn as main memory are ROM or RAM chips
Volatile memory is where storage on device is lost when power source is lost
ROM is permanent storage and is non volatile (data not lost when computer turned off)
ROM stores instructions for the program that runs when the computer is turned on
RAM is used for temporarily storing programs or data being used. It is volatile.
RAM is needed to multitask.. When full uses virtual memory - stored on hard disk temporarily
Typical RAM fitted in a computer increases as production costs fall - rn 4GB to 8GB
Cache is a small memory store directly used by CPU holding copies of frequently used instructions and data
This reduces access time to speed up processing
Data needsto be input before any processing or output can happen. Entered manual or automatic
Data capture is input of data into the system in a suitable form.
Manual : Keyboard, mouse, touch screen, joysticks, webcams, digital camera, digital video camcorder, microphone, remote control, scanner, MIDI interface, Graphic Tablet and Stylus
Graphic Tablet ; More natural to draw diagrams with a stylus than a mouse, allows greater level of accuracy so higher quality drawings./ Not ideal for clicking (mouse job), more expensive & more space
Automatic : Bar code recognition, optical mark recognition, Chip & PIN, Sensors
Bar code : automated output so quick to enter, audible warning of error, prices changed without tags. / new product have to be entered in database, keybad needed if no bar code, could fail
OMR : fast method of inputting list, 1 computer needed for lots, more accurate than person keying. / marks might not be read right, not suitable for text output, special stationary & forms
methods for outputting results from a computer process are : hard copy from a printer or plotter, soft copy from a screen or digital projector, audio output from speakers or headpones, digital outputs to store information for use in another system from DVD or CD-rom
Inkjet printer, laser printer, plotter, speakers, headphones, screen, projector, voice-activated systems, multi-touch gestures, fingerprint recognition utility
Inkjet are cheaper than laser, smaller and lighter, catridges cheaper than laser toners, produce quality photo, cheaper to repair, smaller paper tray. However are noiser than a laser, slow high-resolution colour printing, catridges are smaller capacity, ink can smudge when wet
Plotter have drawing same quality as expert who drew them, larger sizes of paper can be used. / Slower than printers (each line drawn seperately), more expensive than normal printers
Speakers can be used by group, in presentations for speech/sound, blind can use text converted into audio output, need for videoconferencing / disturb others, high-quality can be expensive
Assistive technology for disabled are : eye tracking, sip and puff devices (SNP)
Use RAM as working storage for processing data, volatile storage medium. Means need to use secondary storage devices so copies can be kept.
Common are optical devices, magnetic, solid-state.
Capcity, speed, portability, durability and reliability needs to be considered
Magnetic tape - 80MB to 1TB, low speed, portable, can be damaged by use, reliable, low cost
Magnetic disks - 40GB to 2TB, internal fast, external portable internal not, durable, can crash
Optical disks - 700MB to 4.7 GB, slow, portable, need careful storage, not reliable for long term
Flash memory - 250MB to 64GB, medium speed, small&portable, very durable, very reliable
Solid-State Drives - 128GB to 512 GB, v fast, not portable, durable, most reliable, more cost