Looking Under Lid Of A Computer Computer Science Essay


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A computer is an electronic device that receives data and converts it into information. The von Neumann architecture is a digital computer that was made of very few components; the processor, the RAM (memory), secondary storage (hard drive) and basic input and output devices. This is a detailed report on what is found under the lid of a computer it includes the way certain part of the motherboard work.

The von Neumann model consists of three main categories; the processor, memory and I/O subsystems. The processor processes information, the memory stores information and the I/O subsystem is broken down into two components the input device which sends information to the computer and the output device which gets information from the computer and the control unit makes sure all the other parts perform their tasks correctly and at the correct time.


The processor also known as the CPU (Central Processing Unit) or can also be called microprocessor, which is the brain of the computer. This is located on the motherboard of most computers and most workstations. A central processing unit consists of four main components; these components are the CU (control unit), PC (Program Counter), ALU (Arithmetic Logic Unit) and ACC (Accumulator). These components communicate with each other within the fetch execute cycle. The speed is measured in megahertz (MHz), this is also referred to as the clock speed, and this determines how many instructions per second the processor can perform.

The ACC (accumulator) is a result from the Arithmetic Logic Unit. The CU (control unit) decodes instructions into signals to control components of the CPU as needed to carry out the instructions. The PC (program counter) is not a personal computer; this stores the address of the next instruction in the memory. This is also known as instruction pointer (IP). The ALU (Arithmetic Logic Unit) manipulates data to produce results; all results are represented in binary code. There are two main types of results are logical and arithmetic. An example of logical results is if X is TRUE (1) and Y is FALSE (0), is Z TRUE or FALSE? And an example of the arithmetic result is if A is 1510 and B is 1010, what is Z=A+B?

The processor works in a sequence where by each instruction is read into the CPU from the program memory and then decoded and executed, this is also known as the fetch-execute cycle. This cycle will repeat until the end of the program. Some instructions require additional access to memory for data. This is also known as the instruction cycle or the fetch decode execute cycle.

Diagram 1.0

Binary codes are ones and zeros this is are used to tell the CPU one step of a program these are known as opcodes which means code to show an operation, these depends on the type of computer. Collectively they are called machine code. The benefits of using opcodes are that the user doesn't have to use a number of commands.



Primary memory also known as main memory or internal memory, this is the RAM (Random Access Memory). This is volatile which means it cannot store information whilst the computer is off and is also directly accessible to the CPU and that is the reason any program the user wishes to use must be loaded into the RAM except the BIOS which is stored in the ROM (Read-Only Memory). The CPU constantly reads instructions stored there and runs them when necessary. Any data actively operated on is also stored there the same way.


Secondary memory is non-volatile which means it can hold information even while the computer is off. This type of memory is cheaper than primary memory as primary memory is solid state. This is not directly accessible by a computer which means it must first be copied over to the RAM. This is different from primary storage, such as a hard drive, which is constantly available. It is commonly used for archival purposes. If a computer stops working, a secondary storage device may be used to restore a recent backup to a new system. Therefore, if the user uses a secondary storage device to backup their data, make sure the user runs frequent backups and checks on the data on a regular basis.

Input and Output elements

Before a computer can process any data, the user needs some method to input the data into the computer. The device used will depend on what type of data is inputted. After the computer has processed the data this often produces an output. This output could be audio or printed or displayed on the monitor.

Input devices are peripherals that are used to provide data to the computer. This can be either direct or indirect. Examples of direct input devices are touchscreen monitors and pointing devices such as laser pens. Examples of indirect input devices are mice and trackballs. Direct input devices are almost necessarily absolute, but indirect input devices can be either absolute or relative.

To the User

Output to the user is anything that provides an output to the user such as a printer or a display screens or speakers or headphones.

A printer is a device that prints and electronic document such as an image or text on physical media such as paper; this could be connected to a computer or to a network; this means either one person or many people can print to that one printer. There are many types of printer which have different roles such as an inkjet and laser jet and inkless and dot matrix, these are all used for different things. Laser jet printers are used mainly for speed they are as good as a photocopy machine and produce a high quality output. Inkjet printers are mainly used for high quality printing but may not be as quick as the laser jet and this is done by spraying ink onto the paper. Inkless printers are mainly user in businesses to print out receipts and also used in ATM's this is done by pushing heat pins against heat sensitive paper. Dot matrix printers used a pin to print; a combination of the pins creates a character or an illustration and is mainly used for low cost and low quality applications.

A monitor or a display such as a projector is used to visually show an output to the user and allow the user to see what is happening on the computer. This could be black and white display or gray scale display or color display or TFT-LCD or CRT or OLED. TFT-LCD (Thin Film Transistor Liquid Crystal Display) this is a flat panel display which uses thin film transistor to enhance the display quality, they use the same technology as a normal LCD. TFT-LCD monitors are more energy efficient then CRT monitors. CRT (Cathode Ray Tube) monitors were around in the 1980's and have phased out due to new technology. OLED (Organic Light Emitting Diode) OLED monitors provide a higher contrast and better viewing angle then a TFT-LCD and are replacing them slow as the price is still very high. All the above are now color screen.

Speakers are external to the computer that can be unplugged at any given time; the speakers compatible with a computer normally have a 3.5mm jack which is approximately 1/8 inch. There are also USB speaker which is powered by 5 volts which is provided by the USB port. There are also some which require external power. Some computers come with built in speakers which are powered internally.

From the User

Input from the user is anything that provides an input to the computer. When the user moves the mouse or presses a key on the keyboard this is referred to as input devices.

A computer mouse is a pointing device that allows the user to click on and point to different icons on the computer. This is usually used by one of the user's hands. Some of the mice have more functionality such as scrolling. There are 2 common interfaces which are still used today which are USB and PS/2. The PS/2 mouse has phased out dated due to the new technology of USB. The USB mouse is currently the most popular type of interface. There are also the laser or optical type and the mechanical type of variants.

A keyboard is an input device that normally allows the user to insert text and numbers into a word processor or text editor. The arrangement of keys has been inherited from the typewriter. There are many sizes like the standard size, laptop size and thumb size. Standard size is an alphanumeric keyboard that has keys that are ¾ inch. This is normally used in desktops. Laptop size is used in laptops, netbooks and notebooks, usually smaller and closer together. This size in keyboard doesn't come with a numeric keypad. Thumb size keyboard is normally used for mobile devices like the BlackBerry. This is just a smaller version of the laptop sized keyboard.

Support Elements

A bus is a system that transfers data between devices like a real bus transfers people from location to destination. There are two types of buses; internal and external. Internal buses are known as internal data buses, memory buses or system buses or front side bus or local buses, this connects all the internal components to the motherboard for example a peripheral controller interface expansion card for a monitor also known as a graphics card. External buses or expansion bus is made up of electronic a pathway that creates a connection between different external devices and the computer such as a printer.

A power supply unit supplies and converts high voltage electricity to low voltage electricity for the computer to handle. The power supply unit does not create power. This distributes the power through the computer for all the devices to receive enough power to function fully. Cables are used to connect buses to internal and external devices such as the hard drive which is internal uses an IDE, SCSI, or SATA cable to connect it to the motherboard and a USB A to B or a mini USB cable to connect an external hard drive to the computer. A computing fan is used to cool the computer and allows the flow of coo air from the front of the computer to the back or the side. These come in different sizes; 80 mm, 92mm, 120mm, 140mm or 200mm in width and length. A heat sink is a device that sits on the central processing unit or the graphics processing unit and transfers heat from the central processing unit or the graphics processing unit to the air nearby and a fan usually sits on top of the heat sink to blow the air away.

A computer case holds the motherboard with screws and has dedicated screw holes. It is also referred to as a tower, computer chassis, housing, enclosure or a base unit. This comes in different sizes depending on the size of the user's motherboard. The main material used is steel but can also be made from aluminium, plastic and wood. A motherboard is a printed circuit board. It is also known as system board, mainboard or logic board. This consists of integrated peripherals and peripheral slots for internal and external peripherals such as a central processing unit slot and the RAM slot.


This report discussed the main internal and external hardware components of a modern computer. It was stated that the present computer model is an updated version of the von Neumann architectural computer and therefore has adapted the errors of the von Neumann architecture. As a solution to this problem computer engineers have implemented faster caches to reduce the CPU from needing to access the system buses constantly. This solution does not necessarily eliminate the problem but provides a temporary solution but however as time goes on, so does computer technology. CPUs have become faster and memory sizes have increased but the system bus is still only capable of sending one instruction at a time.

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