A slightly less crude oversimplification divides a computer into five elements: arithmetic and logic subsystem, control subsystem, main storage, input subsystem, and output subsystem. processor arithmetic and logic control main storage external storage input/output overview input output processor The processor is the part of the computer that actually does the computations. This is sometimes called an MPU (for main processor unit) or CPU (for central processing unit or central processor unit). A processor typically contains an arithmetic/logic unit (ALU), control unit (including processor flags, flag register, or status register), internal buses, and sometimes special function units (the most common special function unit being a floating point unit for floating point arithmetic). Some computers have more than one processor. This is called multi-processing. The major kinds of digital processors are: CISC, RISC, DSP, and hybrid. Altogether, a computer system is a tool that can be used to read and write stories, draw and look at pictures, and send and receive messages. There are many other things that a computer system can help you do as well, like math and science experiments. Computer systems are especially good at storing large amounts of information and helping you find exactly what you want to know. A computer system is like a magic box with more magic boxes inside. No matter how many boxes you open, there are always more inside. If you open the computer system box, inside you find a keyboard, a monitor, a computer, and other boxes that might be printers or extra disk drives or networks or many other things This is the computer ... A computer is the heart of a computer system. A computer is like a box that sits in the middle of all of the other boxes in the computer system and listens to them and tells them what to do. A computer can store and find words and pictures and sounds and cartoons, and even video and show them all to you by telling the monitor what to do. You can tell the computer what you want to see by typing on the keyboard, and the computer will listen to it and find what you want. Like all the other boxes that make up a computer system, if you open up a computer box, you find more boxes inside. There are four kinds of boxes inside a computer: 1. the logic board 2. the disk drives 3. the power supply 4. "special boxes" that may not be necessary, but let the computer do all kinds of useful things The logic board (or "motherboard") is where most of the work inside a computer is done. Just like the computer is the heart of a computer system, the logic board is the heart of a computer. The logic board does all of the math and comparisons and other work needed to move text and pictures and sounds and video from one part of the computer to another and to solve the problems that you give the computer system. It also talks to other parts of the computer system to tell the monitor what to show and to listen to the keyboard. The disk drives are like big filing cabinets where text and pictures and sounds and video are stored. There are many kinds of disk drives. Most computers have a "hard disk drive," a "floppy disk drive," and a "CD-ROM drive." A hard disk drive always uses the same disk and holds lots of information that can be written, read, erased, and re-written. A floppy disk drive can use many different disks (but only one at a time). These disks hold a little bit of information that can also be written, read, erased, and re-written. A CD-ROM drive can use many different disks (like a floppy disk drive), each of which holds a lot of information (like a hard disk drive). Unlike a hard disk drive or a floppy disk drive, a CD-ROM drive cannot write or erase the information on its disks. It can only read the information, and that’s what the "ROM" in CD-ROM means: "Read-Only Memory." The power supply takes electricity from the plug in the wall and makes sure that all of the other parts of the computer get the right amount of electricity at the right time. The other things inside of a computer may not be necessary, but they do very useful things, like let the computer talk to a network or let the computer record video and sounds. This is the monitor ... A monitor is like a box with a window on the front. The computer system uses this box to show you some of the things that are going on inside of the computer. Some of these things may be text or pictures that are stored inside of the computer. Some of these things may be the results of calculations that the computer is doing. Some of these things may be events or information that are from a long way away . A monitor works because of a substance called "phosphorus." Phosphorus glows brightly when it is stuck by electrons. The glass on the monitor is coated on the inside with phosphorus. At the back of the monitor is a gun that shoots a steady stream of electrons at the front of the monitor. This gun is called a "cathode." Sometimes, a monitor is called a "CRT," which stands for "Cathode Ray Tube." Magnets surrounding the cathode can direct the electrons very precisely. These magnets move the stream of electrons back and forth across the screen, from top to bottom, causing some of the phosphorus to glow, while other parts of the phosphorus are left dark. The monitor can do this so fast, that it can cover the whole screen 30 times a second. To make colors, a monitor uses three kinds of phosphorus that glow red, green, and blue when struck by electrons. By making more or less of the phosphorus glow in these three colors, the monitor can make almost any color you want. This is the keyboard ... A keyboard is like a box with many buttons on it. When a button is pressed, it sends a signal to the computer. Each button has a different code, so the signal that goes to the computer tells the computer exactly which button was pressed. The computer then uses this code to decide how to respond to the pressed button. For example, when you press the button with a "J" on it, then the keyboard sends a signal to the computer telling it that the "J" button was pressed. If you are writing a message to your friend when you press the "J" button, then the computer will probably put the letter "J" into your message. However, if you are playing a computer game when you press the "J" button, the computer may decide to make your character jump up and down. It all depends on what you are doing. A keyboard has two sets of intersecting wires. One set has a wire for each row of keys; the other set has a wire for each column of keys (on standard United States keyboards, the first column is "1" "Q" "A" "Z"). Each key is really a switch. When it the key is pressed, the switch is turned on for one row wire and one column wire. Each combination of one row wire and one column wire names exactly one key on the keyboard. The key marked "Shift" is different from the regular keys. When it is pressed and held down, it adds information to the signal that is sent when any other key is pressed. Other keys that act like the "Shift" key are the "Control" or "Ctrl" key and the "Option" or "Alt" key. This is the mouse ... A mouse is like a little movable box that can point to different pictures or words on your monitor screen and tell the rest of your computer system what to do. As you move your mouse, a small "pointer" (cursor) displays on your screen. You can use it to point at a picture or word that you wish to select, then "click" (press down) on one of the buttons on the mouse. Depending on what you are viewing, selecting an object or word can perform many functions. Selecting an object or word could cause a different page to display on your screen, or tell your system to do something special like run a program, or even to turn itself off! A mouse has a little rubber ball inside that helps you to move it over the surface of your desk or "mouse pad". When you move the mouse, you are actually rolling the little ball inside. The mouse is connected to the rest of your system by a special cord that sends and receives bits of information. As the mouse moves, it sends information to the computer system which tells the pointer to move also. When you press down or "click" on one of the mouse buttons, you are also sending information to the computer system, telling it what to do. Motherboard Form Factors The form factor of the motherboard describes its general shape, what sorts of cases and power supplies it can use, and its physical organization. For example, a company can make two motherboards that have basically the same functionality but that use a different form factor, and the only real differences will be the physical layout of the board, the position of the components, etc. In fact, many companies do exactly this, they have for example a baby AT version and an ATX version. AT and Baby AT Up until recently, the AT and baby AT form factors were the most common form factor in the motherboard world. These two variants differ primarily in width: the older full AT board is 12" wide. This means it won't typically fit into the commonly used "mini" desktop or minitower cases. There are very few new motherboards on the market that use the full AT size. It is fairly common in older machines, 386 class or earlier. One of the major problems with the width of this board (aside from limiting its use in smaller cases) is that a good percentage of the board "overlaps" with the drive bays. This makes installation, troubleshooting and upgrading more difficult. The Baby AT motherboard was, through 1997, the most common form factor on the market. After three years and a heavy marketing push from Intel, the ATX form factor is now finally overtaking the AT form factor and from here out will be the most popular form factor for new systems. AT and Baby AT are not going anywhere, however, because there are currently just so many baby AT cases, power supplies and motherboards on the market. These will need an upgrade path and I believe that at least some companies will make motherboards for the newer technology in AT form factor for some time, to fill this upgrade market demand. A Baby AT motherboard is 8.5" wide and nominally 13" long. The reduced width means much less overlap in most cases with the drive bays, although there usually is still some overlap at the front of the case. There are three rows of mounting holes in the board; the first runs along the back of the board where the bus slots and keyboard connector are; the second runs through the middle of the board; and the third runs along the front of the board near where the drives are mounted. One problem with baby AT boards is that many newer ones reduce cost by reducing the size of the board. While the width is quite standard, many newer motherboards are only 11" or even 10" long. This can lead to mounting problems, because the third row of holes on the motherboard won't line up with the row on the case. (Some reduce or skip the third row entirely). Fortunately, it is almost always possible to solidly mount the motherboard using only the first two rows of holes, and then using stubbed spacers for the third row. See the Motherboard Physical Installation Procedure for more perspective on these issues. Baby AT motherboards are distinguished by their shape, and usually by the presence of a single, full-sized keyboard connector soldered onto the board. The serial and parallel port connectors are almost always attached using cables that go between the physical connectors mounted on the case, and pin "headers" located on the motherboard. The AT and Baby AT form factors put the processor socket(s)/slot(s) and memory sockets at the front of the motherboard, and long expansion cards were designed to extend over them. When this form factor was designed, over ten years ago, this worked fine: processors and memory chips were small and put directly onto the motherboard, and clearance wasn't an issue. However, now we have memory in SIMM/DIMM sockets, not directly inserted onto the motherboard, and we have larger processors that need big heat sinks and fans mounted on them. Since the processor is still often in the same place, the result can be that the processor+heat sink+fan combination often blocks as many as three of the expansion slots on the motherboard! Most newer Baby AT style motherboards have moved the SIMM or DIMM sockets out of the way, but the processor remains a problem. ATX was designed in part to solve this issue. The physical motherboard's function is to provide a useful, working place for all of the components of the PC to interface. The physical motherboard's function is to provide a useful, working place for all of the components of the PC to interface. THE BASIC PARTS OF A COMPUTER CD-ROM Drive- reads information stored on Compact Discs. Click – A click often selects an item on the screen. To click, press and release the left mouse button. Floppy Disk Drive – A floppy drive stores and retrieves information on floppy disks. Hard Drive – A hard drive is the primary device that a computer uses to store information. Keyboard – A keyboard is a device that lets you type information and instructions into a computer. Monitor – A monitor is a device that displays text and images generated by the computer. Mouse - A device that fits in the palm of your hands. It is used to select, activate and manipulate features on the screen. If you are right handed, the index finger rests on the top left section: the middle finger on the top right section.