The Fetch Execute Cycle Computer Science Essay

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1st Jan 1970 Computer Science Reference this


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Within this report about Computer Hardware, the report will cover the main concepts of computer hardware. Within this report there will be information about the main concepts of a computer system also. These main concepts will include Processors, Memory (Primary and Secondary), Input and output devices under the user types and networking, and support elements that will help the overall performance of a computer.

Processors are parts of the computer that heart and brain of every computer, as it allows the processing of data in the computer system as well as the allowing instructions to be stored onto memory. The processor communicates with all the components of the computer. It mostly helps with the hardware, memory, and RAM of the computer or laptop


The CPU or central Processing unit is the most important and without the CPU the system would not be about to process anything. The Primary usage of the CPU is when instructions for the computer are created. Instructions are taken to decode a number of data types from programs. The CPU has to implement 4 basic functions during the fetch execute cycle; these are Fetch, Decode, Execute and Store (Hubapges, 2012).

Fetch-execute cycle

The Fetch-execute cycle is the sequence that the CPU gets an instruction from a certain program memory, decodes the incoming message and carries out that certain request. (Rob Williams, (2006) p52-54). Each of the instructions has an address, and the processor takes the address from something called the program counter. The program counter is in charge for tracking what instructions the CPU should execute. In basic teams instructions from memory being tracked (Hubpages (2012).

The Following are the stages from inside a Fetch-execute Cycle


Once the CPU fetches the instructions, decodes the instruction, and then strips it down so that it can be easily executed (Complete PC Pedia. 2010). However some CPUs understand different types of instructions. For Example Assembly codes must be decoded into binary instructions. (Hubpages, 2012).

Execution -After the decoding has been executed, memory is needed for data to be performed. For example a command to print is given when the first instruction has reached the CPU.

Store – after the execution, the CPU writes the results onto the main memory or on a register. The CPU must then give some feedback after execution. Then output data is written to the memory.Made in a presentation owned by De Montfort University, copyright them.

To the right is a diagram that shows the basic stages of the fetch-execute cycle Shane Preece. (2008)


Whenever the processors execute instructions, data is temporarily stored in local memory locations of 8-64 bits called registers. The type processor the machine owns depends on the overall number of registers which can vary from ten to many hundreds and even thousands. There are many types of registers but the main ones are listed below.

Accumulator register which stores arithmetic operations, as well as logical one;

Status register holds system status indicators such as overflow;

Instruction register contains the current instruction being processed;

Ordinal counter contains addresses of the next instruction; ( (N/A))

Examples of other Processors


A microprocessor is a circuit that has been integrated on a tiny silicon chip that contains millions of tiny switches on/out, known as transistors. These are laid along microscopic lines that store or manipulate data. These circuits copy data in patterns, and these patterns that can be programmed by software to help the machine do many useful tasks. (Belarus network. (2009).)

Graphics processing unit (GPU)

The Graphics Processing Unit is somewhat like the CPU (Central Processing Unit). GPU is a single-chip processor. While the CPU acts like the brain of the system, the GPU is primarily used for the computing 3D functions. For example lighting effects, object transformations, and 3D motion. ( (2012))


Memory is split into two parts. Primary and Secondary

Primary memory is one of the most important parts of a computer. The processors inside the computer stores and retrieves information from the memory and is accessed by the CPU in a random order making RAM or random access memory. So any location of this memory can be accessed by the CPU to store or read.

Random Access Memory, or RAM, is the most common under the major types of Semiconductor memory. RAM has the ability to both read data from memory and also is able to write new data into memory really easy and incredibly fast. Both reading and writing is done via electrical signals. However RAM is classed a volatile. This is when the memory is deleted when there is no power resulting in the loss of data. Leading to RAM used only as temporary storage. RAM also has two different types being DRAM and SRAM. (William Stallings (2006). 148-149.)

DRAM or Dynamic memory is made with cells that hold data as charge on capacitors. The showing of charge in is the binary code of 1 or 0 when present or absent. DRAM is used in main memory. (William Stallings (2006). 148-149.)

SRAM or static random access memory is made up of 1000’s of flip-flop circuits. While SRAM is the much fastest between the two, it is the most expensive of read-write memory. The SRAM is the fastest on-chip cache memory. Also compared to DRAM, it is low power consuming and is brilliant for battery-powered portable machines. SRAM is used in cache memory. (Rob Williams (2006). p121.)


Read only memory contains patterns of data that cannot be edited or changed. ROM is classed as non-volatile, meaning no power supply is needed in order to maintain the bit values in the memory. ROM is what it is, read only, cannot be changed or rewritten. One of the best things about ROM is that all the data or program is always located in the main memory and it will never be needed to be loaded into some form of secondary storage device. (William Stallings (2006). 148-149.)

Cache Memory

Cache Memory lies between main memory and CPU. The Cache memory is random access memory that the computer’s microprocessor can access more quickly than it’s RAM. When the microprocessor processes data, firstly it takes a look in the cache memory and if it finds the data there. ( (N/A)).

Cache memory is local memory that causes waiting times for information stored in the RAM (Random Access Memory). This overall effects the speed performance of the computer’s main memory making it slower than that of the processor, but at the same time are certain types of memory is faster, but has greatly increased costs. Cache memory is sometimes put into levels of closeness or accessibility to the microprocessor. An example of a cache level is L1 cache; this is on the same chip as the microprocessor, or L2 is usually a separate static RAM (SRAM) chip. The main RAM is usually a dynamic RAM (DRAM) chip. (SearchStorage (2000)).

Cache also reduces the latency time of memory when transferring information. When the processor is in operation, L1 cache can interface with L2 controllers to transfer information Also the L2 cache interfaces with the RAM (level three caches) to allow transfers. ( (N/A)).

Virtual Memory

Virtual memory today is now very common, as virtual memory can be located in all types’ computers and operating systems. Virtual memory can even be found in the smallest microprocessor to the largest supercomputer. However Virtual Memory is not real, physical memory, as it is a type of storage space so large that programmers do not need to edit the programs or documents in way shape or form. Whenever the content of a program is loaded the amount of a local memory is changed. (Peter J.Denning. (1996). p213-216.)

Secondary memory

Secondary is the slowest and cheapest form of memory that money can buy. It stores the data permanently unless it is erased however itt cannot be processed directly by the CPU so it must be manually copied from primary storage. Secondary Memory can include types such as magnetic disks, optical disks and sometimes magnetic tapes. WikiAnswers. (2012).

Magnetic disks

Magnetic disks are data that is encoded on disks. This enables the user the ability to store information on a magnetic disk as many times as you want as well as erase it. Examples are Hard Drives and Floppy Disks

First is the floppy disk : One of the first types of secondary memory, floppy disks consists of a typical 5¼-inch floppy disk that can hold 360Kb or 1.2MB. However 3½-inches normally store 720Kb, 1.2MB or 1.44MB of data. Webopedia. (2012).

The Hard disk is the most common secondary data as they are used in almost every computer system as they provide A LOT of data for the operating system, files, music and games that you want to store on the machine. Hard disks can store from 20MB to more than 200GB. Hard disks are also 10 to 100 times faster than floppy disks. Webopedia. (2012).

Removable cartridge hard disks encased in a metal or plastic cartridge, so you can remove them just like a floppy disk. Removable cartridges are very fast, though usually not as fast as fixed hard disks.

Optical disks

Optical disks record data by burning microscopic holes in the surface of the disk with a laser. To read the disk, another laser beam shines on the disk and detects the holes by changes in the reflection pattern. Webopedia. (2012).

CD-ROM : Most optical disks are read-only. When you purchase them, they are already filled with data. You can read the data from a CD-ROM, but you cannot modify, delete, or write new data. Webopedia. (2012).

Input and Output elements

The input and output devices are another important part for a computer system. Devices you use will depend on what kind of data needs to be inputted onto the machine then a output will be produced of the results. This certain output can be displayed via a computer screen, printed page, and even the audio.

Input and output elements can be either for the user or network.

Below are some of the main input elements for the user


A keyboard is one of the most common parts of a computer system that is used to enter text into the computer and display it to the screen. The keyboard can also be used to type commands, such as an on-screen menu using a mouse. Plus most keyboards these days are not just used for typing text, but also most now have numeric keypad, editing keys and a row of function keys along the top. UNM-LA. (2004).


A mouse is by far the most common pointing input device for computers. With the working mechanics of a ball on its underside that rolls on a flat surface causes the pointer on the screen to move. The mouse allows you to reposition the pointer on the screen that shows where the next interaction with the computer can take place. The cursor can also be moved by pressing different keyboard keys. N/A. (N/A).


Scanners are special devices that copy images from a hardcopy source and then copy’s it to the screen making a digital copy. It works by the image being converted to numerically and sent to the computer for very colour weather it is light or dark. Scanners normally scan graphic pages however they can be used to scan text pages using the OCR or Optical Character Recognition. UNM-LA. (2004).

Types of Screens

Cathode ray tube or CRT monitors display text and graphics are some of the most common used today. Another type of screen flat panel display usually uses an LCD (Liquid Crystal Display) screen to display output from the computer. A flat display often seen on watches and calculators. LCD screens are used on laptop computers. Some LCDs are monochrome, but colour screens are popular. Some laptop screens are nearing CRTs in resolution quality. N/A. (N/A).


Trackballs are like a mouse variation that is used to play video games. The trackball is basically an upside-down mouse-you roll the ball directly with your hand. N/A. (N/A)

Below are some of the main output elements for the user


Today the most common printer would have to be ink jet printer as they produce for hardcopy output. These printers print a on the page by spraying ink to the page. However these printers need a lot of ink. Also a common printer is laser printers. These printers produce some of the best kind of image quality. NM-LA. (2004).


Computers Speakers produce output via sound also, from very basic beeps, to some of the best sounds via game sound effects or music. Basic sounds may be on the motherboard, but high quality audio are from speakers that output from a PC which can be inserted to in a expansion slot,. UNM-LA. (2004).

Networking inputs and outputs


Modems use data communications via a dial-up or broadband connection that allows computers to exchange data. The normal telephone modem offers communication rates from 300-56000bps. For a modem, it contains two different types of translators.

The first is the Modulator which transmits digital signals out down the phone line in analogue form. While the demodulator receives analogue signals from the phone line and converts them back into digital form. Rob Williams (2006)


A hub is one of the most basic networking devices, which can connect ma number of computers or network devices together. Unlike a network router, network hubs have no routing tables where they can send information and broadcasts. Most hubs can detect basic network problem’s such as collisions, however if there is multiple ports being used, the risk of security risks can increase. With hubs, they serve as central connection points for local area networks (LANs). Also there are not just box hubs, but USB ones as well. Computer Hope. (2012)

Support Elements

Support elements for a computer are to help the computer system. This can be classed as performance aiding such as increasing the computer’s performance, elements such as making the computer not suffer from a system failure due to overheating and even elements that help support the whole computer by keeping it protected or helping it work.

1. The use of support elements below are elements that transfer information between components


A system bus is a special set of physical connections such as cables, which are shared by multiple hardware components in order to communicate with each other

The purpose of system buses is to reduce the number of “pathways” that are needed for communication between computer’s components, by carrying out all communications over a single data channel.

Below is a diagram of a bus and it shows how a simple bus change can be put into place to make the flow of data simple and not complex., compared to the one on the left. . ( (n/a))

schematic diagram of a bus

A system bus is sorted by the amount of information that is transmitted, which is shown in bits. For example a 32-wire ribbon cable can transmit 32 bits in parallel. While the speed of the bus speed is called frequency and shown as Hertz which is the number of data packets sent or received per second. This is known as a cycle. ( (n/a))

System Buses are split up into three distinct groups. They are Data, Address and Control.

Data buses are normally 32 bits wide but can be increased to bits of 64

Address buses are 32 bits but will require more space soon

Control bus- about 15 lines responsible for starting and stopping activities (Rob Williams( 2006)(p56-59)

Fiber Cable

Fiber optic cable are cables that are made of a very clear glass tube that transmits light to and from a system. Light will travel down the tube in a straight line. The light jumps off of the mirrors in the wire and is directed back into the fiber optic core to continue its journey along the cable. Michelle Miley. (1999).

The next type of support elements are to put power in and take excess power out

The power supply is hands down the most vital part of any computer system. The power supply converts the AC or alternating current from your home to the direct current or DC.

In a PC or personal computer, the power supply is a large metal box usually found in a corner of the case with or next to the fans. The power supply is visible from the back as it contains the power-cord receptacle and the cooling fan. Gary Brown. (1998).


One of the main components in a compute is a fan. An example of this can be found in the CPU as there is a CPU fan. Fans are one of the most effective ways to cool down the computer’s processor and protect the computer from overheating and damaging the system. The CPU fan actively cools the processor by bringing in cooler air. Also cooling fans are available in a many of sizes. The CPU’s cooling fans are attached directly to the top of the CPU, and works together with an aluminium heat sink fan. They cool down the CPU and reduce the amount of hot air from circulating around in the computer case.

Heat sink

An aluminium heat sink fan is a cooling device that draws heat away from the computer’s components into its large surface area to transfer cooler. This cooling device works at the same time as everything else in the computer. NMB. (2010).

The next types are support elements to hold and support the components

The Case

The computer case can be the aluminum, steel and/or plastic shell that protects all of the computer’s components. Computer Cases are built to support a certain sets of hardware, in other words not all motherboards, optical drives or other hardware may be compatible with a particular computer case as the size maybe incompatible. Some computer cases come with power supplies or other essential hardware preinstalled.


A motherboard holds all the main elements of the computer or laptop together. Located on the motherboard, the CPU must be matched a slot in the motherboard so that it may fit into the motherboard’s sockets. The Motherboard allows the communication of electrical signals to pass through the computer. Without it the computer would be nothing more than an empty shell.


In conclusion, this report has cover the main attributes of computer hardware being the processor, memory, Input and output elements and support elements. The processor is the brain of the computer and the CPU or central processing unit is the main type of processor in front of the microprocessor and the CPU uses the fetch-execute cycle.

While memory covered primary and secondary. Primary being main memory accessed by the CPU and examples are RAM, ROM, Registers and cache. Secondary is stored information, and examples are Optical and Magnetic. While Input/output elements include Keyboards, mouse’s, screens, printers (user) and Modems and HUBs (network). Also support elements are system buses, cables, power supplies, cases and motherboards that help the performance of the machine.

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