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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > ICT > Complete GCSE ICT Note for AQA Exam Board
Data
- Bit- each individual ‘1’ or ‘0’ is a bit-short for binary digit.
- Byte- 8 bits are a byte.
- Kilobyte-is 1000 bytes (1024)
- Megabyte-is 1,000,000 bytes
- Gigabyte-is 1,000,000,000 bytes
- Each character on keyboard-8 bit
Computer systems v Manual systems
- Benefits of computer system:
- Takes up less space
- Searching is very quick
- More than one person can access the same data form their network PC.
- The data stays in the computers memory
- Fewer staff are needed to look after a computer system
- Reports can be generated very quickly-automated
- Problems of a computer system:
- Setting up is very expensive
- Computer systems need people to maintain them
- POWER CUTS!
- It is easy to hack into a computer system.
Types of computer
- Mainframes-biggest
- They are the most powerful
- They are very large
- VERY expensive
- They are used in BIG businesses-banks, insurance companies.
- Minicomputers-middle
- Less powerful than mainframe but more powerful than micros
- Microcomputers-most common-usually called PC’s.
- Are designed to stand alone
- Much less powerful than mainframes.
Networks-LANS AND WANS
- Local area network-LAN-small-offices and schools.
- Wide area network-WAN-large-link together different places.
- Advantage of using networks-peripherals such as printers can be shared amongst several users.
- Software can be shared amongst several users.
- Communication across network is fast + cheap
- Disadvantage of using networks-cabling can be expensive to install and replace
- A fault with the server will prevent the whole network from working
- Security measures are needed to restrict access to network
- WANS are vulnerable to hackers and viruses.
'Networks-security
- SERIAL NUMBERS
- ALARMS
- DOORS
- FIRE PROTECTION
- LOCK
- AVOID
- BLINDS
- Passwords-should be changed frequently.
- Backup-and files should be kept secure-in locked fireproof rooms.
Input devices
- Keyboards
- Mouses-touchpad, tracker balls.
- Graphics pads make drawing easier and more accurate.
- Joystick
- Scanner
- OCR scanners-read text
- MICR-magnetic ink character recognition-cheques
- OMR-optical mark recognition-registers-read lines in boxes.
- Credit cards have a magnetic stripe on the back-carries info so the computer can identify the customer.
The CPU
- The control unit makes the system work-CU
- It controls all hardware attached to the system.
- It controls the output and input of data
- It controls the flow of data within the CPU
- The ALU is where the processing happens-Arithmetic and logic unit.
- Arithmetic part-does calculations!
- Logic part-makes decisions like whether a number is bigger than –5.
- The IAS is where active data is stored.
- IAS-immediate access store
Output devices-PRINTERS
- Advantage of dot matrix-cheap and low operating costs.
- Disadvantage of dot matrix-low res, slow, noisy.
- Advantage of laser-high res, very fast
- Disadvantage of laser-expensive.
- Advantage of inkjet- good res, cheap
- Disadvantage of inkjet- slow (ish), expensive to run
Data storage-ROM and RAM
- RAM is temporary-random access memory
- It stores data as electric signals.
- If the power is cut or electricity fails everything in RAM-LOST!
- ROM is permanent-Read-only memory
- ROM however is not a backing storage on hard disk.
Backing storage
- Hard disk-main internal storage.
- Large capacity-range from 20gb to 100gb!
- Floppy disk-3.5 inch
- 1.44 mb-very small capacity
- Magnetic tape-used to backup large amounts of data-cheap as well!
- Access time is slow because it has to run through whole disc to find something.
- Optical disks have fast access time.
- CD-ROMS-oldest type-650mb
- CD-R’s-sold as blanks-data can be written only once to it.
- CD-RW’s-most popular. RW stands for read and write.
- DVD-17 gb
- ZIP disks-larger, thicker-100mb
Operating systems
- Enable applications to run
- Enables software to communicate with systems hardware
- It manages system resources
- Monitors performance of system
- Prompts error messages.
- Multi tasking means an OS can run more than one program at a time
- Basic systems that are not multi tasking are called single program mode OS’s.
User interfaces
- Can be command driven-blank screen and commands and code used.
- Can be menu driven- headings and menus
- Most common is GUI-graphical user interface-combines menu driven and icons-
- GUI’s are known as WIMPS-windows, icons, menus, pointers
Data capture
- Data capture turns info into data
- Automatic data capture-is fast and accurate
- BUT manual data capture- is necessary sometimes, and it’s cheaper!
Data validation and verification
- Validation-4 checks
- Range check-checks data is in specified range
- Presence check-makes sure data is present
- Check digit-check that numerical data is accurate
- Data type-checks that text is not where numbers are meant to be.
- Verification-2 checks
- Proof reading-read it and make sure that its accurate
- Double-entry-data entered twice and compared
- Validation problems- mistakes may be allowed if carried out wrong and only makes sure that data is right type-NOT ACCURATE.
- Verification problems-double entry is time consuming-expensive and proof reading is time consuming and does not eliminate human error.
Data processing
- Real time processing does it instantly
- Batch processing-all in one go
- Transaction processing-one off specials
- Interactive processing-talk to the computer
Access to data
- Serial access-records are stored one after another in creation order
- Sequential access-records are stored one after another acc. to sensible order
- Direct access-can go to record directly
Implementation and evaluation
- 3 types of implementation-
- Direct-straight away and old system goes down but bugs not picked up in testing-bad news!
- Phased-different parts are introduced one at a time
- Old system is kept running
- Parallel-new system is introduced in one go BUT old system stays
- New system can be tested quickly but all tasks need to be done twice.
- Evaluation just checks that the system meets all objectives
- DTP SOFTWARE-is good because it creates pro. Looking documents and the layout can be changed more easily than word processors and the user can control the number of pages more easily than a word processor
INTERNET
- The Internet is basically a very big WAN.
- To connect you need a PC connected to a normal telephone line and a modem
- You use your modem to dial up a computer that is owned by an ISP
- You need 2 pieces of software- email client and web browser.
- Internet has 2 main parts-WWW (world wide web) and email.
- Speed of access depends on 3 things-
- Modem speed-either 28kbps or 56kbps
- Telephone line-either ISDN or ADSL
- Volume of traffic-more people using the Internet, the slower the speed of access.
- Http-hypertext transfers protocol-language that web uses.
Health and safety
- RSI- repetitive strain injury-aches pains and muscle or tendon damage
Spending too long in front of a VDU can cause eyestrain and headaches.
Circulation and fitness and back problems result from sitting all day in front of a computer
- Solutions-
- Take regular breaks, look away from screen walk around and exercise fingers
- Use correct equipment- a chair with a backrest, a keyboard making it easier to type without straining
- Good background lighting, good screens and a screen filter to reduce VDU glare.
Comments
Hi, i hope these help you with revision. they did a fantastic job in my class, because with just a few exceptions every single boy in my class got an a/a*. if you are on the AQA board, and are doing ICT, learn these notes and i can really guarantee that you'll pass. make sure you read it a few times til it sticks in your head!!!
good luck..
