What is a Computer System

What is a Computer System
Computer Systems
Hardware 1
Revision Notes
Computer Systems : Hardware
What is a Computer System?
The different parts of a computer, including the devices
you plug into it are collectively called a Computer System.
Hardware is the name used for all the physical parts of the
computer system.
The devices connected to the computer are called
The Central Processing Unit (CPU) is a chip which powers
the computer. It can be thought of as the brain of the
computer. It does all the calculations and carries out all the
The processor’s speed is measured in Megahertz (MHz
million cycles per second) and this determines how fast
programs run. Some modern computer can operate at GHz
speeds. This means that they can carry out a thousand
million instructions every second.
Main Memory
The computer has two types of memory to store data.
Read Only Memory (ROM) stores the instructions that
tell the computer how to start working. This is
permanent memory and cannot be changed.
Random Access Memory (RAM) stores data while the
computer is working but loses it when switched off.
This is temporary or volatile memory. Having a large
amount of RAM can improve the overall performance of a computer. Most
modern computers have at least 1GB of RAM.
The motherboard is the main circuit board inside
the computer.
It connects the CPU, ROM, RAM, disc drives,
graphics cards and audio cards.
Computer Systems : Hardware 1
Input Devices
What are Input Devices?
Input is the information a user puts into the computer. To input information the
user needs input devices. Input devices capture information from the user,
convert it to an electrical signal and then pass it to the processor.
This is one of the most commonly used input devices.
It is used to input text and numbers to the computer.
Keyboards are very useful for many types of tasks.
The standard keyboards which we use are called QWERTY
keyboards. Can you guess why?
A mouse is a pointing device. Moving the mouse makes the
pointer on the screen move in the same direction.
It is also used to select options by clicking the buttons. Some
mice have a wheel which can be used to scroll around the
screen quickly.
There are two main types of mice. Those with roller balls on
the underside and optical mice which work using light beams.
Scanners are used to make digital files from a paper
This could be a photograph or even a piece of text.
Scanners are optical devices since they use light beams to
digitise (convert into 1s and 0s) the source document.
Digital Camera
Digital cameras are input devices. They have many
advantages over film cameras. No film needs to be bought.
The images are available straightaway on the built in LCD
screen. The images can be edited on the camera or
transferred to a computer for more advanced editing.
Computer Systems : Hardware 1
Output Devices
What are Output Devices?
Output is the information you receive after completing a process. Output devices
convert an electrical signal into pictures, sounds or motion so that information
can be passed back to the user from the processor.
Monitors are the most commonly used output devices on
personal computer systems. We look at them all the time
to get results back from the computer.
A high resolution monitor gives a good sharp, clear image.
This is essential for detailed work and prolonged use as it
is much clearer and less tiring to view. Modern Liquid
Crystal Display (LCD) monitors a less bulky and take up
less space than older Cathode Ray Tube (CRT) monitors.
The output from a printer is called a hardcopy. When choosing a printer there are
several factors to consider: cost to buy, cost of ink/toner, resolution
Resolution is measured in dots per inch (dpi). Speed is measured in pages per
minute (ppm)
Ink Jet printer
These are very affordable printers. They are the most common
type of printers to be found in the home. This is because they
can print high resolution images in colour and are quite cheap
to buy. The ink for them can be expensive however so they are
not very good if a high volume of printing is to be done.
Laser printer
This type of printer is much more expensive to buy, but it is
more economical to run if a lot of printing is to be done. It
can print high resolution images and tends to print faster
than inkjets. The most affordable laser printers will have only
black toner and produce greyscale output. Colour laser
printers are more expensive.
Computer Systems : Hardware 1
Backing Storage Devices
Data Units
1 bit
binary digit
8 bits
1024 bytes
1024 KB
1024 MB
1024 GB
What are Backing Storage Devices?
When a computer is switched off or an application is closed the current data will
be lost. In order to keep our data permanently we need to save it using a backing
storage device.
Data can be stored using internal or external storage devices. Internal storage
devices are inside the computers system unit. External devices are separate from
your computer.
Hard Disc
Hard Discs are usually connected to the motherboard
and fitted inside the system unit. They are internal
storage and not portable. Modern hard discs have a
very high storage capacity and can store a huge amount
of data. Contemporary computers have a data capacity
of a few hundred GB. Some even have TB (tera bytes).
Hard discs store the data using invisible magnetic
patterns so they are also called magnetic discs.
Optical Discs
CDs and DVDs store data using laser beams which are a form of
light. These are therefore called optical discs. These are both
external storage media as they are separate from your computer.
They are therefore portable and can be used to take data from
one computer to another. Compacts Discs can store around
700MB of data.
Digital Versatile Discs have a larger capacity and can store between 4.7GB and
17.1 GB.
Flash Storage
Flash drives have become very popular as portable backing
storage. This is because they are very small, cheap and have a
reasonable data capacity. The data is stored on non-volatile
computer memory chips that can be erased and rewritten.
Computer Systems : Hardware 1
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