Computer studies notes for syllabus section 5, 4.1 and 4.2.
What is a computer?
It is an electronic device capable of inputting, storing, processing and outputting data under the control of a stored program.
Terms you need to know
the physical components of a computer system eg. Mouse keyboard etc.
The programs/instruction which tell the computer what to do.
Eg. System software – the operating system
Application software – the operating system application software – A word processor, utility software – format a disk.
- Input – a way of putting in data/ information to a computer system erg. An input DEVICE is a mouse.
- Output – way of putting out data (information from a computer eg. An output DEVICE is a printer.
- Device – a physical component eg. A hard disk DRIVE, a processor.
- Medium – a component used by a device eg. Paper (printer medium)
DISK (used to store data on by a disk drive) CD (used by CDROM drive)
- Peripheral – A device externally connected to the CPU
Eg any input / output / secondary storage device
- Arithmetic and Logic Unit – The part of a processor that carries out any arithmetical or logic operations eg. Add 2 numbers etc.
- Control Unit – The ‘part’ of the processor which synchronises / organises the way instructions are carried out.
- Main (primary) storage – This is electronic memory which allows fast access to data.
RAM Random Access Memory stores the data and programs currently being processed. RAM is temporary / volatile meaning it loses its contents when the ‘power’ is switched off.
ROM – Read Only Memory stores data which needs fast access and its permanently stored – even when the power is switched off.
- Secondary (backing) storage
Permanent storage of data/software by storage devices onto storage mediums. Eg. A hard disk drive saves data onto a hard drive. Some of these devices use magnetic methods: hard disk/floppy disk optical methods: CD.
Section 5 hardware
Differences between a laptop and a desktop pc
Microprocessors can be found in many domestic devices. Eg.
· Mobile phone These are called ‘embedded’
· Gaming console processors. They are ‘fixed’
· Calculator into the device and contain
· DVD player ‘built’ in programs.
Some devices store their programs in ‘flash memory’. This allows you to change the contents. Usually the manufacturer provides you with updated ‘FIRMWARE’.
Firmware is software stored on a hardware memory device.
Digital cameras are ‘embedded’ devices. They contain a microprocessor with programs stored in firmware. The user selects the settings by inputting the selection using ‘buttons’ and ‘dials’ (some cameras have a joystick or touch screen).
Cameras have a number of sensors (devices which measure physical quantities and outputs a voltage corresponding to the measurement)
- Light sensor
- Focus sensor
- Movement (anti-shake) sensor
- Image sensor
The signal from the sensor is a voltage – an analogue quantity. The processor requires the data to be in digital format i.e. 0’s and 1’s. An analogue to digital converter (ADC) or digital to analogue converter (DAC) is required.
ALL data stored in a computer system is saved as a number! These numbers represent CODES. They are stored as BINARY number.
Eg the ‘character’ A might be stored using the ‘ASCii’ coding system for character ‘ASCii’ code for A = 65(base 10) = 01000001
Eg. ASCii code for B is 66(base 10) = 01000010
Eg. The code for the ‘colour’ white could be 255(base 10) = 11111111
1. Binary is used in computers because the units that are used to design the circuits can be ether ON or OFF. i.e 1 or 0 – the same values we can use BINARY.
2. The programs (applications) you use interpret the codes. Eg. A word processor might interpret 66 as A.
A graphics program might interpret 66 as the colour blue.
There are many different types of data which can be used. Eg. Text eg Ben, numeric eg 27.35, date eg 10/10/2010, Boolean eg true (or false).
The different data types are stored in different ways. Eg. CAT would be stored as 3 bytes – 1 for each character using ASCii code.
Eg. 66 (integer) 01000010 (1 byte)
Verification and validation
- Checking that data entered into a computer system is the same as the original/source data. Eg. You type in your password twice when changing it and the computer confirms that they are the same.
Eg. You ‘swipe’ your dinner card and the teacher verifies you are the owner by comparing the photo displayed and you!
Eg. 2 different ‘users’ enter the same data and the computer compares them. Any differences are indicated to the ‘users’.
‘Checking’ that the data meets rules specified for that data.
Eg a test is marked out of 100,
Validation rule: an integer } TYPE CHECK
Validation rule: 0≤mark ≤100 } RANGE CHECK
Eg a password must have 2 letter followed by 3 numbers.
Validation rule: LLØØØ } FORMAT CHECK
L = character (letter)
Ø = digit
Validation rule: must have 5 ‘characters’ } LENGTH CHECK
Other validation ‘checks’
- Presence check: is there any data present eg when filling a form and there a fields which must be filled in.
(NB) could use validation rule: length > 0 } LENGTH CHECK
Applying information you have acquired to make sense of a situation/solve a problem.
- Ability to understand information and to then form judgement, opinions, make predictions based on that understanding.
Mount Everest is 29029 ft high
Mount Everest, 29029
My name is Fred and I am in form 7J
Mougins School has 437 students
Mougins School, 437
Direct data entry input devices
1. Optical mark reader (method: recognition)
Application – multiple choice.
‘Shine’ a light at predetermined positions on the input medium (paper). The amount of reflected light is measured. Light areas – more light, dark areas – less light.
Application – recording electricity/water/gas readings.
2. Optical Character Reader (recognition)
- recognises characters in a character set from an input medium.
- uses the method of light refection
- uses a ‘template’ for each character to try to recognise it.
- The ‘code’ for the recognised character is stored.
- converting text documents to machine format
- postcodes on letters
3. Magnetic Ink Character Reader (recognition)
- Ink has ‘magnetic’ properties
- The magnetic (used) areas are detected
- Compared with pre determined templates of characters
- Recorded as ‘character code’
- Used on bank cheques to reduce fraud (difficult to change characters)
3. Barcode reader
- uses light (laser) to recognise where light/dark lines are. These lines represent a code (s)
eg on a product in a supermarket
- manufacturers code
- item code
- check digit
- biometrics – finger prints – retina
- voice recognition
- magnetic ‘strip’ readers
- smart card
Recording data – file processing
- data is stored in files. Processing can be done on that data:
- edit (change – modify
Types of file access
1. Serial access – data is stored/retrieved one item (record) after another. The data is not in any particular order.
E.g. the data about items bought at a ‘point of sale’ in a supermarket would be stored serially i.e. in the order at which the items were scanned.
2. Sequential Access
E.g. data recorded about the temperature in a room is stored in time sequence.
Items of stock might be stored sequentially (in order of item ID)
3. Random or Direct Access
Data is stored in a way so that individual records (or items of data) can be accessed directly.
E.g. recording student records where we need to access individual records directly (and quickly).
E.g. in a stock control system where we need to find the price of an individual item e.g. for use at a point of sale (POS).
- Sort files into different orders (by date, size, type etc)
- Organise by using folders
- Different views (icons, file names etc.)
- Rename files
- Delete files
- Copy files
- Move files
Backup and Archive
- Backup – take a copy of ‘current’ working data and store it on another storage device (possibly in a different location). You may make more than 1 copy!
- The frequency of saving depends on the application. In school we backup all data once a week (at report time we backup report data every 2 hours!).
- Full backups – backup all data
Incremental backups – backup only data/files which have changed since last backup.
Removing non-current data from the main storage system onto another storage device. (This data can still be accessed if necessary)
E.g. In school we could archive data for the previous school year at the start of the year.
E.g. a shop could archive sales figures for the previous ‘accounting’ year.