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The Von Neumann Computer is a digital pc that stores the data in a single separate way and it use a processing unit. A digital computer keeps its program in instruction with its data as well. The Von Neumann Computer named after name of computer scientist John von Neumann. the Von Neumann Architecture is the simplest structure or framework design that a computer's hardware, programming, and data should follow. It consist of one shared memory for instructions and data with one data bus and one address bus between processor and memory. Instructions and data have to be fetched in sequential order (known as the Von Neumann Bottleneck). It is mostly used to interface to external memory. Here is some description of the Von Neumann computer main elements;
File:Von Neumann architecture.svg
Central Processing Unit (CPU)
Processor or Central Processing Unit (CPU) it is part of computer system and in easy way to describe it's the brain of computer. The job of CPU in a computer is to give an instruction for numeric data (data in a binary) and to execute the instruction code to store in primary or secondary memory (Kioskea.net, 2010).
So how this small piece of metal and plastic operates and run our computer and why we are calling it the brain of the computer? Mainly the CPU is the brain of computer is because it controls all the process carry through the computer from typing to transferring data to a distant computer(2). There are some elements inside the CPU that are working together to make the processor functional such as:
Arithmetic Logic Unit (ALU)
The Fetch Execute Cycle of CPU: it is an order of actions that the central processing unit (CPU) perform to execute each machine code instruction in a program. The Instruction Register IR) which holds the last instruction to be solved and executed. After that is the Program Counter (PC) which contains the address of the next instruction to be fetched from memory. When a processor needs to read or write data to/from the memory it specifies the address on the address bus and the data is then placed on the data bus. The control bus then determines whether the memory is being read or written and it sends signals to the CPU or the memory depending whether the data is being read or written. These signals tell the CPU/ Memory that the data is on various buses. Once the first instruction has been fetched, it decodes the instruction and it then executes this data and then fetches the next instruction and repeats the process (2). There are some main elements in the Fetch Execute Cycle which are:
Control Unit: Control unit which give direction to the data around the CPU by sending control signals and it's job is to control the data that executed by the ALU, also the Control Unit keeping communicate with ALU and system memory (book).
The Arithmetic Logic Unit (ALU): This is the most important elements of processor because the ALU is responsible for working out of the calculation needed through the processor (2). Brown and Kruger (2010) are saying "the ALU has direct input and output access to the processor controller, main memory (random access), and to the output/input devices". Every input is contain of machine instruction word that has an operation code which is also called "OP CODE". This Op Code instructs the ALU to what operation is need and what operands are needed to perform the operation. For example if the user enter a number to subtraction it's the ALU job to solve the calculation and output the result to the any output device. The ALU perform all the arithmetic operations such as subtraction, adding, division or multiplying.
Registers: It is another device type that existed inside the processor. The register is a short term memory and its task is to save for the short term the result outcome from other devices such as ALU (2). The register is not a main memory part; it is on the chip which outfit by the CPU. Register hold and transfer instructions. Register operate faster than a Ram, normally register assess by bit like 32 bits (book).
Busses: the bus job is to transfer data between inside CPU components also its job is to create a bridge path of communication between the main bus and the CPU inside a computer (4). There are different kinds of bus inside the CPU which are:
Data bus: its job is to transfer the data bytes inside the processor elements (articlealley). For example the Arithmetic Logic Unit (ALU) transfers the result to the register by the data bus.
Address bus: this type of buses is used to fetch certain data from memory based on the number on the address bus. For example if the address bus has a binary value of 1101. Then it will fetch the value in memory in that address. Thus the address bus tells the processing units where to find the data in memory or where to put the computed data in memory.
Control bus: this type of buses is used to transfer control signals between elements of the processor. For example, when an instruction is decoded that it has addition operation, it will inform the ALU that the operation is addition by putting certain value on the control bus. When the Processor decodes this value it will understand that the operation is addition based on the value on the address bus.
In the computer memory is used to store the data and programs, and there are two types of memory in a computer which is primary memory and secondary memory:
It is a very fast memory and it is task is to store the programs and active data. Primary memory is a semiconductor memory and it consist of a large number of semiconductor storage cells, each one of the cell normally hold one byte each one of the cell has an address which is referred to as a memory location.
Random Access Memory (RAM): It is a temporary computer internal memory and it is a space that allows us to temporarily store data when a program is running. The contents are being lost when the computer is switched off it only holds data while power is on.
There are some major types of RAM which are:
Rambus DRAM (RDRAM): is a serial memory technology that arrived in three flavours, PC600, PC700, and PC800. PC800 DRAM has doubled the maximum throughput of old, but a higher speed and it use small capacitors to store each bit of memory in an addressable format that consists of rows and columns, DRAM designs with multiple channels (15).
SIMM chips: Single in-line memory modules (SIMMs) it is a type of solid state computer memory which is used particular for the processor cache memory. The 72-pin SIMM has a notch among the contacts in the middle. An important characteristic of RAM is that the entire memory place can be accessed at almost the same speed (15).
Read Only Memory (ROM): Is a kind of memory that store the data permanently and it cannot be removed. Every computer comes with a small amount of ROM which is a record of boot firmware. When we start our computer the ROM chips will run the hardware diagnostics that will load the operating system into RAM (15).
Virtual Memory: The virtual memory task was to enable a process to operate or establish the status of pages in its virtual address space.
The secondary memory comparing to the primary memory is cheaper and slower. The CPU cannot access to secondary memory, therefore any data must copied into primary memory first. Computer requires large storage and this storage are formed in magnetic disk, magnetic tapes and optical disk this storage call the secondary memory (book).
Magnetic Hard Disk: In the magnetic hard disk the data are recorded in a magnetically form and it re-record over and over again. The hard disk has a large magnetic circular plate material and it is called a platter which is divided into billions small areas (10). Every part of these small areas is able to magnetize to store 1 or to demagnetize to store 0. The data can go on even the computer goes off and it only can be demagnetize by us.
The data on hard disk stored in file forms, a file is a cluster of bytes, these bytes could be any information such as a software instruction for computer to execute or a JPEG image but it doesn't matter what it contain it is just a file is simply a string of bytes(9). When the computer runs a file it start to retrieve from hard disk and the hard disk send its bytes to the CPU one at a time.
CD Rom: The standard size for a CD is 4.75inches in diameter and 0.05inches is thickness and it's made of a polycarbonate plastic and its layer made of aluminium and coating lacquer. CDs store the files and songs in digital format and this information it shows in a series of 1s or 0s. The data storage in CD and CD-ROM is characterized in two modes. Mode1 is for storing the computer data and Mode 2 is for audio, video file etc...(12).
CD-ROM Mode 1 :The data is store in sectors (Smallest addressable of information), each of these sectors are able to hold 2,352 bytes of data but for mode 1 (which is for data storage) these sectors is broken down to 2,048 is used for storing the data and 304 bytes of data is used for error detection(12). The disks have 75 sectors/second which represent the CD capacity of 681,984,000 bytes and its rate of transfer speed is 150 KBps, the 2X, 8X, 6X so on is representing the drive speed in a multiplies single speed transfer rate.
CD-ROM Mode 2: As we mentioned before the Mode 2 is used for storing Video/Audio in CDs, for detecting error and correction it use only two layers and the rest of data 2,336 bytes is available for user to store data on it. In the mode 2 the amount of data that can be saved is varies significantly and its reason is the use of sync and header bytes, detecting error and correction (12). In the Mode 2 it allocates various data to be mixed with each other, offer storing video and graphic in a flexible method and the CD in mode 2 can be read by a normal drives of CD-ROM.
The data in CD-ROM has encoded into the spiral track, the start and the centre and the ending in the furthest edge of CD disc. This spiral track can hold nearly 650 MB of data which is equal to 5.5 billion bits (12).
Flash Memory: When it comes to storing the data fast and easy that is flash memory is used for, it is an electronic memory in various types. Flash memory is a solid storage device; there are no magnetic parts so everything is electronic (13).
Transistors are like MOSFETs (metal-oxide-semiconductor field-effect transistor) in a flash memory which has only two doors on its top. One of these doors is called a floating gate and second is called control gate. The electric current cannot pass between this two gate because their separated by oxide layer (14). By applying positive electrons voltage to its transistor in between two interactions which is called Bitline and Wordline electrons move in very fast from resource to drain. A few of the electrons will manage to wriggle in the oxide layer and will stuck in the floating gate: and this wriggling of electrons inside the floating gate stores one in the flash transistor (14). Even the supplied power to the circuit is turned off the electrons in the flash transistor will stay there without letting up. Putting a negative voltage into the wordline will clear the electrons from the flash transistor and store zero again.
Input and Output elements
Keyboard: A keyboard is a device used to input text and data. In computing a keyboard uses an arrangement of buttons or keys, to act as unconscious levers or a keyboard is a device used to input text and data. The keyboard is used to type text and numbers into a word processor, text editor or other program. When we press a key, it presses a button, completing the circuit and allowing an amount of current to run through. The keyboards are connected by USB cable or PS2.
Mouse: The purpose of the computer mouse is to open things we can't open with the keyboard. The mouse is a device which controls the movement of the cursor on a display screen. It is a small object which we can roll along a hard, flat surface. As we move the mouse, the pointer on the display screen moves in the same direction. Mice contain at least one button and sometimes as many as three, which have different functions depending on what program is running. A mouse is connected by USB cable or PS2.
Printer: A printer is a peripheral which produces a printout or hard copy of documents stored in electronic form. The speed of printers can be measured in characters per second. Early printers were measured in units of characters per second whereas the modern printers measured in pages per minute. Printers are designed for low-volume, short-turn around print jobs. The printer is connected directly to the motherboard via a USB gold cable. The gold USB cables are considered best for connectivity and transfer.
Monitor: A monitor or display is a piece of electrical equipment which displays images. The size of a display is usually given as the distance between two opposite screen corners. The images from monitors originally contained only text, but asÂ Graphical user interfacesÂ emerged and became common, they began to display more images and multimedia content. The monitor is connected with the motherboard through DVI cable. DVI cables are very popular with video card manufacturers, and most cards nowadays include one or two DVI output ports.
Support Elements (such as; power supply, Motherboard, Network Slot)
Power Supply: Power supplier is the element that supplies power to the computer. The most common type of power supply is plugging into electrical outlets. The AC current is then converted to DC current by that power supply. It attempts to efficiently regulate voltage but this is not universal with all power supplies so voltage fluctuations are common. Old PC motherboards had Power suppliers directly soldered. Nowadays power suppliers are connected via a 20 pins ATX power connector that gets plugged into an attached socket on the motherboard. Some motherboards need extra power which is supplied throw an additional 4-pins ATX 12V connector.
Motherboard: The motherboard is the main route board of the computer. As we know the CPU is the brain of the computer whereas the motherboard is the heart of it. This is where we usually find the CPU and RAM clipped to. In meantime we can choice the type of CPU and RAM as the variety of motherboard we have. The motherboard can also be a deciding factor when we buy a new graphics card too.
Video cards: Video cards let computers to show video and computer graphics. Some video cards allow computers to show television the same as control frames from video. In mean time a video card allows computers users to produce live video and a high speed connection is necessary for successful video conduction. We connect the auxiliary power to our video card. The topmost expansion slot on the motherboard and the monitor should be connected to the card.