A computer system is made up of a combination of hardware and software.
All of the electronic and mechanical equipment in a computer is called the hardware. Examples
• Hard disk
• Power supply
The term software is used to describe computer programs that perform a task or tasks on a
computer system. Software can be grouped as follows:
System software: These are the programs that control the operation of the
computer system. Operating systems and utility programs are the most common. The
Operating System starts the computer, provides a user interface, manages the computer
memory, manages storage, manages security and provides networking and internet
facilities to mention a few of it’s capabilities. There are many OS’s on the market
including Microsoft Windows XP, Microsoft Windows Vista, Apple OS X , Unix and
Linux. Windows is by far the most commonly used OS in the world, but Linux in
particular, is making inroads into this dominance.
Utility programs perform maintenance tasks on the computer system. This includes
file management programs, uninstall programs, disk scanners and fragmentation,
backup utilities, antivirus etc. These can be included in the OS or purchased
Device drivers are programs that control particular hardware devices. They are
supplied with new hardware and must be run so they the hardware can communicate
with the OS. They are supplied with printers, graphics cards, scanners etc.
Application Software: This software is used to do non-system based tasks.
Categories include business software, engineering software, medical software,
Sometimes, application software packages are grouped together to form
productivity suites. Examples include Microsoft Office and OpenOffice.
These combine word processing, spreadsheet, database and presentation
software with a common interface making then easier to learn. The Adobe
Creative suite combines Adobe Photoshop, Adobe Illustrator, Adobe In Design
etc. as an all-in-one graphics and web design suite. As well as common
interfaces, these suites offer great compatibility between the applications.
A computer system is a collection of electronic and mechanical devices operating as a unit. These
devices can be sorted according to the role they play in the computer system. The main device
The main parts of a computer system are:
- Input devices :These devices are used to get data into the computer system.
Processing devices :These manipulate the data using to a set of instructions called a program.
Output devices :These are used to get data out of a computer system.
Storage devices : The can store the data for use at a later stage.
Communications devices :These can send the data to another computer system .
1 System Unit : The container for the motherboard, disk drives etc.
2 Monitor : The main output device for the system.
3 Keyboard : The main input device for the system.
4 Mouse : An input device allowing interaction with the system using pointing and clicking .
5 Speakers :Used to output sounds and music from the system .
mechanical devices from damage. Typical system unit devices include:
• CPU (Processor)
• Disk drives
• Expansion cards - sound card, graphics card, network card etc.
• Ports - USB etc.
• Power supply
Peripherals are devices that connect to the system unit using cables or wireless technologies.
Typical peripherals include:
The Processor (CPU)
A processor is an integrated circuit (IC) supplied on a single silicon chip. All of the components
and pathways necessary for the movement of data around the processor are etched on this single
The processor’s function is to control the activities of the computer system. A computer program
is made up of instructions and when the program is run, the processor is responsible for carrying
out these instructions in an orderly fashion. The type of instructions the processor can execute
• Arithmetic instructions - It carries out all the addition, subtraction, multiplication
and division requested by computer programs.
• Logical instructions - It can make decisions by comparing data and acting in a
particular way depending on the result.
• Move operations - It can move data from place to place within the computer
system. This could be from memory to the processor for
addition or from memory to a printer or disk drive etc.
The speed of a processor is measured in megahertz (MHz) or Gigahertz (GHz). This is the speed
of the system clock (clock speed) within the processor and it controls how fast instructions can be
• 1 MHz - One million clock ticks every second
• 1 GHz - One billion clock ticks every second
This means that if one instruction was executed every clock tick, a 3GHz processor could execute
three billion instructions every second.
The two main computer processor manufacturers are Intel and Advanced Micro Devices (AMD).
These two companies produce almost all of the processors used in desktop and notebook
• Intel - Intel makes the Pentium and Centrino ranges of processors.
• AMD - AMD makes the Athlon and Turion ranges of processors.
The performance of these chips relative to each other is forever changing and it would be difficult
to claim one is better than the other in the long term.
The latest trend in processor manufacture is to essentially put more than one processor on a silicon
chip. These multi-core processors can have two, three or four processor cores on a single chip.
This obviously vastly increases the performance of the computer system as long as the programs
run on the systems can take advantage of the multi-cores.
Another important factor in processor choice is the amount of power a processor consumes. This
is not critical on a desktop computer but is critical on a notebook computer. AMD and Intel have
developed a range of processors optimized for mobile computers. The Turion and Centrino
processors use very little power to maximize battery life and are optimized for wireless
networking, factors that are very important in mobile computing. They also use Speed step or
Power now technology to regulate the processor power to the system requirements.
Word processing needs less processor power than CAD and the system can adjust the processor
speed to suit the program being run. This saves power and produces less heat. In a notebook
computer, this is a huge advantage.
Known as primary storage, it is the main working memory of the computer system. Data and
programs currently in use are held in RAM. It is called random access because data can be
accessed in any order. If you are working on a drawing in Solid works, the Solid works program
and the drawing under construction are both held in RAM. RAM is volatile which means that
when the computer is turned off, the contents of RAM are lost. This is why it is essential to save
your work on a regular basis. Because of the volatility of RAM, most software programs have an
auto save feature to prevent the total loss of your work.
RAM is made in the form of integrated circuits (IC’s) in the same manner as a processor. These
IC’s are placed on a circuit board to produce a memory module. The most common RAM
technology is dynamic random access memory (DRAM).
In this technology, a transistor and a capacitor are paired to store one Bit (binary digit) of data.
In essence, if the capacitor is charged, a binary 1 is stored and if it is discharged, a binary 0 is
stored. (see the section on data representation for more on binary data). The transistor acts as a
switch to allow the capacitor’s state to be changed as required.
There is a problem with this technology. As soon as the capacitor is charged, it begins to leak. As
a result, the charge in the capacitors must be continually refreshed or they would leak to binary 0’s
resulting in corrupted data. This continuous refreshing is performed about 80 times per second and
drastically slows down the speed at which main memory can be written to and read from.
DRAM is sold in modules called DIMM’s (dual inline memory module) for desktop computers
and in modules called SODIMM’s (small outline dual inline memory module) for notebook
HP 4GB - 1600 DIMM Memory
SO-DIMM RAM 4GB
DIMM’s and SODIMM’s are sold in modules with capacities of 256MB, 512MB, 1GB, 2GB. The
current technology is called DDR (double data ram) and there are three types. Any particular
computer system can only use one of the three type. The types are:
As can be seen from the above tables, the type of memory in a computer can have a massive
impact on the overall performance of the computer system. At the extremes, DDR-200 can be
accessed 200 million times per second while DDR3-12800 can be accessed 1600 million times per second.
If a computer system has a Pentium IV processor running at 3GHZ and 512MB PC-2100 DRAM
installed, every time the processor requires data from RAM it will have to slow down to the speed
of the RAM (PC-2100 = 266MHz) to access the data. As the processor continually accesses RAM,
the effective speed of the processor for these transfers will be 266MHz. This is called latency and
would effectively ruin the performance of the computer system if allowed to continue.
To overcome this problem, a small amount of fast static RAM is included in the processor. Static
RAM does not use capacitors and as a result does not need to be refreshed. Static RAM is much
more expensive to produce than Dynamic RAM and as a result is not suitable for use as main
memory in a computer.
When the processor wants to read from a memory location, it first checks the cache for the
location. If the location is in the cache, the processor can access the data without accessing main
memory - the location is accessed at the speed of the processor. This is called a cache hit. If the
location is not in the cache, then main memory must be accessed at the slower speed and this is
called a cache miss.
This small cache memory (typically 128KB) is called Level 1 cache (L1) and is on the processor.
A second cache called Level 2 cache (L2) is situated on the motherboard near the processor and
can be from 1MB to 8MB in size. This cache is slower than level 1 cache but still much faster
than main memory.
If a processor requires data from a location in RAM, the level 1 cache will be searched first. If the
location is not in level 1 cache, level 2 cache will be searched. Only if the location is not in level 2
cache must the slow main memory be accessed.
Modern computer systems have cache hit rates in excess on 90% and this has a huge bearing on
the overall performance of the computer system.