GCSE ICT REVISION NOTES

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1. Computers, data and information
A computer is an information processing machine. Computers process data to
produce information. The sets of instructions that humans give computers are
called programs or software. Software that carries out a particular type of task for a
user is often called applications software.
Reasons for using computers
Computers can work much faster than humans.
Computers do not get tired or need a rest.
Computers can do jobs that it would be dangerous for human to do.
Computers can store large amounts of information in a very small space
Computers can find information very quickly
Computers never lose or misplace information.
Three stages of computing:
Input, processing and output
A computer runs through these stages by `running' a program. A program is a set of
step-by-step instructions which tells the computer exactly what to do with input in
order to produce the required output.
Input
This stage of computing is concerned with getting the data needed by the program
onto the computer. Input devices are used to do this. The most commonly used
input devices are the mouse and keyboard.
Processing
The instructions about what to do with the input are contained in a program. During
the processing stage, the computer follows these instructions using the data which
has just been input. What the computer produces at the end of this stage is called
output.
Output
This stage of computing is concerned with producing the processed data as
information in a form that is useful to the user. Output devices are used to do this.
The most commonly used output devices are the screen, which is also called a
monitor or visual display unit (VDU) and the printer.
Data and information
Data is any collection of numbers, characters or other symbols that has been coded
into a format that can be input into a computer or processed. Data on its own has no
meaning or context. It is only after processing by a computer that data takes on a
context and becomes information.
There are many types of data. All data ends up being stored as a series of numbers
inside the computer (binary code). Data can be input to the computer by the user in
many different ways. The main types of data that can be input into a computer and
processed are numeric, text, dates, graphics and sound.

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Computer Systems
Hardware is the name that is given to any part of a computer that you can actually
touch. An individual piece of hardware is called a device. The basic hardware of any
computer consists of a central processing unit (CPU) along with input, output and
backing storage devices.
The central processing unit (CPU)
This is the part of the computer where the searching and sorting of data, calculating
and the decision-making goes on.…read more

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Keyboard
The keyboard is the most common type
of input device. Ordinary computer
keyboards have their keys arranged in a
similar way to those on a typewriter.
This way of arranging the keys is called
QWERTY because of the order that
they keys appear in on the first row of
letters.
Pointing devices
A mouse is a pointing device. It is the next most common
type of input device after the keyboard. Touch pads and
trackballs are also types of pointing device.…read more

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Graphics Tablet
A graphics table consists of a flat surface and a pen, or
stylus, which can be used to produce freehand drawings
or trace around shapes. When the special pen touches
the surface of the graphics tablet data about its position
is sent to the computer. This data is used to produce on
the screen an exact copy of what is being drawn on the
surface of the graphics tablet.
Microphone
A microphone is used to input sound into a computer system.…read more

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Bar codes
A bar code is a set of lines of different thicknesses that represent a number. Bar
Code Readers are used to input data from bar codes. Most products in shops have
bar codes on them. Bar code readers work by shining a beam of light on the lines
that make up the bar code and detecting the amount of light that is reflected back.
Bar codes represent a code number for a product.…read more

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If both entries do not match up the data
is rejected.
Validation
Validation checks are carried out by software to make sure that data which has been
entered is allowable and sensible. Data that is not sensible or allowed is rejected by
the computer. There are many different types of validation check that software can
make on data. We will now look at some of these in more detail.…read more

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Hash total
Hash totals are used to check that groups of numbers have been input correctly.
A hash total is the sum of a group of numbers that are going to be input. The hash
total is input along with the numbers. The computer calculates a hash total for the
numbers that have been input.…read more

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Advantages of coding values:
Fewer key presses are needed when entering a value in the field so there is less
chance of the wrong keys being pressed
Time is saved when entering data because there is less to type in each time
Database packages allow automatic validation checks to be set up to make sure
that only the allowed codes have been input in a field.
5.…read more

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Memory which is not wiped clean when the computer is
turned off is called non-volatile memory.
PROM and EPROM
PROM and EPROM are both special types of programmable read only memory.
PROM stands for Programmable Read Only Memory. This type of memory can be
programmed once but can not be changed again afterwards. EPROM stands for
Erasable Programmable Read Only Memory. This type of memory can be
programmed and then changed whenever necessary.…read more

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Magneto-Optical disks which can have data written to them any number of
times just like a hard disk.
Digital versatile disk (DVD)
DVD is the latest way of storing data. DVD discs are expected to replace ordinary
compact discs and video tapes in the future. A DVD disc can store up to 17 gigabytes
of data. This is enough storage space for at least four full-length feature films!
Magnetic Tape
Magnetic tape comes in two forms; tape reels and cassettes or cartridges.…read more

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