Computer Components

CPU (Central Processing Unit)
So what's a CPU? It stands for Central Processing Unit. Many users erroneously refer to the whole computer box as the CPU. In fact, the CPU itself is only about 1.5 inches square. The CPU does exactly what it stands for. It is the control unit that processes all* of the instructions for the computer. Consider it to be the "brain" of the computer. It does all the thinking. So, would you like to have a fast or slow brain? Obviously, the answer to this question makes the CPU the most important part of the computer. The speed here is the most significant. The processor's (CPU's) speed is given in a MHz or GHz rating 3 GHz is roughly 3,000 MHz. In today's computers, the video cards, sound cards, etc. also process instructions, but the majority of the burden lays on the CPU.
MotherboardThe best way to describe the motherboard goes along well with my human body analogy that I used for the CPU. The CPU is the brain, and the motherboard is the nervous system. Therefore, just as a person would want to have fast communication to the body parts, you want fast communication between the parts of your computer. Fast communication isn't as important as reliable communication though. If your brain wanted to move your arm, you want to be sure the nervous system can accurately and consistently carry the signals to do that! Thus, in my opinion, the motherboard is the second most important part of the computer. The motherboard is the circuit board to which all the other components of the computer connect in some way. The video card, sound card, IDE hard drive, etc. all plug into the motherboard's various slots and connectors. The CPU also plugs into the motherboard via a Socket or a Slot.
Hard Disk
As the primary communication device to the rest of the computer, the hard drive is very important. The hard drive stores most of a computer's information including the operating system and all of your programs. Having a fast CPU is not of much use if you have a slow hard drive. The reason for this is because the CPU will just spend time waiting for information from the hard drive. During this time, the CPU is just twiddling it's thumbs... The hard drive stores all the data on your computer - your text documents, pictures, programs, etc. If something goes wrong with your hard drive, it is possible that all your data could be lost forever. Today's hard drives have become much more reliable, but hard drives are still one of the components most likely to fail because they are one of the few components with moving parts. The hard drive has round discs that store information as 1s and 0s very densely packed around the disc.
Video cards
Video cards provide the means for the computer to "talk" to your monitor so it can display what the computer is doing. Older video cards were "2D," or "3D," but today's are all "2D/3D" combos. The 3D is mostly useful for gaming, but in some applications can be useful in 3D modeling, etc. Video cards have their own advanced processing chips that make all kinds of calculations to make scenes look more realistic. The many video cards out there are based on much smaller number of different chipsets (that are run at different speeds or have slight differences in the chipsets). Different companies buy these chipsets and make their own versions of the cards based on the chipsets. For the most part, video cards based on the same chipset with the same amount of RAM are about equivalent in performance. However, some brands will use faster memory or other small optimizations to improve the speed. The addition of other extras like "dual head" (support for two monitors) or better cooling fans may also appear by different brands. At any rate, the first decision to make is what chipset you want your video card to use. If you aren't interested in games, then the choice of chipset isn't too difficult - just about any will do for the 2D desktop applications. There's no point in buying a video card over $100 if you don't plan to play games.
Memory
All programs, instructions, and data must be stored in system memory before the computer can use it. It will hold recently used programs, instructions, and data in memory if there is room. This provides quick access (much faster than hard drives) to information. The more memory you have, the more information you will have fast access to and the better your computer will perform. Memory is much like the short term memory in your brain. It holds your most recent information for quick access. Just as you want to accurately remember this information in your head, you want your computer's memory to have the correct information as well, or problems will obviously occur. Bad memory is one of the more common causes of computer crashes, and also the most difficult problem to diagnose. Because of this, making sure you get good RAM the first time around is very important. There are many, many different types of memory for different tasks. The main ones today are DDR PCxx00 SDRAM DIMMs (this includes PC2700, PC3200, etc.) and Direct RDRAM RIMMs.CD/DVD-ROM Drive
CD-ROM drives are necessary today for most programs. A single CD can store up to 650 MB of data (newer CD-Rs allow for 700 MB of data, perhaps more with "overburn"). Fast CD-ROM drives have been a big topic in the past, but all of today's CD-ROM drives are sufficiently fast. Of course, it's nice to have the little bits of extra speed. However, when you consider CD-ROM drives are generally used just to install a program or copy CDs, both of which are usually done rarely on most users' computers, the extra speed isn't usually very important. The speed can play a big role if you do a lot of CD burning at high speeds or some audio extraction from audio CDs (i.e. converting CDs to MP3s).
CD-R/RW (which stands for Recordable / Rewritable) drives (aka burners, writers) allow a user to create their own CDs of audio and/or data. These drives are great for backup purposes (backup your computer's hard drive or backup your purchased CDs) and for creating your own audio CD compilations (not to mention other things like home movies, multimedia presentations, etc.).
DVD-ROM drives can store up to 4 GB of data or about 6 times the size of a regular CD (not sure on the exact size, but suffice to say it's a very large storage medium). DVDs look about the same and are the same size as a CD-ROM. DVD drives can also read CD-ROM drives, so you don't usually need a separate CD-ROM drive. DVD drives have become low enough in price that there isn't much point in purchasing a CD-ROM drive instead of a DVD-ROM drive. Some companies even make CD burner drives that will also read DVDs (all in one). DVD's most practical use is movies. The DVD format allows for much higher resolution digital recording that looks much clearer than VCR recordings.
DVD recordable drives are available in a couple of different formats - DVD-R or DVD+R with a RW version of each. These are slightly different discs and drives (although some drives support writing to both formats). One is not much better than the other, so it really boils down to price of the media (and also availability of the media).
SCSI card
A SCSI card is a card that will control the interface between SCSI versions of hard drives, CD-ROM drives, CD-ROM burners, removable drives, external devices such as scanners, and any other SCSI components. Most fit in a PCI slot and there is a wide range of types. The three main types of connectors on these cards are 25-pin for SCSI-1, 50-pin for Narrow SCSI, and 68-pin for Wide SCSI (and Ultra-Wide SCSI, Ultra2-SCSI, Ultra160 SCSI, and Ultra 320 SCSI - all of which use a 68 pin connector).
SCSI controllers provide fast access to very fast SCSI hard drives. They can be much faster than the IDE controllers that are already integrated your computer's motherboard. SCSI controllers have their own advanced processing chips, which allows them to rely less on the CPU for handling instructions than IDE controllers do.
For the common user, SCSI controllers are overkill, but for high end servers and/or the performance freaks of the world, SCSI is the way to go. SCSI controllers are also much more expensive than the free IDE controller already included on your motherboard. There is also a large premium in price for the SCSI hard drives themselves. Unless you have deep pockets, there isn't much of a point in going with a SCSI controller.
Many people buy SCSI controllers just for use with their CD-ROM burners and CD-ROM drives (these drives must be SCSI drives of course).
SCSI cards also have the ability to have up 15 devices or more per card, while a single IDE controller is limited to only 4 devices (some motherboards now come with more than one IDE controller though). SCSI cards allow these drives to be in a chain along the cable. Each drive on the cable has to have a separate SCSI ID (this can be set by jumpers on the drive). The last drive on the end of the cable (or the cable itself) has to "terminate" the chain (you turn termination on by setting a termination jumper on the drive - or use a cable that has a terminator at the end of it).
Monitors
Monitors obviously display what is going on in your computer. They can run at various resolutions and refresh rates. 640x480 is the default resolution for the Windows operating systems (this is a low resolution where objects appear large and blocky). 640x480 just means that 640 pixels are fit across the top of your monitor and 480 up and down. Most users prefer higher resolutions such as 800x600 or 1024x768 all the way up to 1600x1200 (and higher for graphics professionals). The higher resolutions make objects smaller, but clearer (because more pixels are fit in the screen). You can fit more objects on a screen when it is in a higher resolution. Larger monitors are better for running at the higher resolutions. If you run a high resolution on a small monitor, the text may be hard to read because of its small size, despite the clarity. The refresh rate is how fast the monitor can refresh (redraw) the images on the screen. The faster it can do this, the smoother your picture will be and the less "flicker" you will see. The monitor has a lot to do with the quality of the picture produced by your video card, but it doesn't actuall "produce" the graphics - the video card does all this processing. But, if your video card is producing a bright detailed picture and your monitor is dim and blurry, the picture will come out the same way.
Printer
As you know, a printer outputs data from your computer on a piece of paper. There are many different types of printers (most common are laser and inkjet), and many printers are better than others for different tasks (printing photographs, clear text, etc.). Laser printers aren't necessarily better quality than inkjets anymore, although they once were. If you want to be able to print in color, inkjet printers are the best option for the cost conscious too. Some of today's "office inkjet" printers also have other functions including scanning, faxing, copying, etc. While the scan and copy quality usually aren't that great, the quality is generally good enough for most office / home office situations.
Modem
If you are at home, then you are most likely using a modem to view this page right now (dial-up modem, cable modem, or DSL modem). The modem is what hosts the communication between your computer and the computers you are connecting to over the Internet. If you're on a network, then you're using a network card (Ethernet card most likely - and that may connect to your cable or DSL modem). A modem uses your phone line to transfer data to and from the other computers. Newer cable modems and DSL modems provide about 10 times the speed of a regular phone modem. These are usually external and plug into a network card in your computer.Modem stands for "modulator / demodulator" and it encodes and decodes signals sent to and from the network servers. Good modems should be able to do all the encoding / decoding work on their own without having to rely on your computer's CPU to do the work.

First Generation Electronic Computers

Three machines have been promoted at various times as the first electronic computers. These machines used electronic switches, in the form of vacuum tubes, instead of electromechanical relays. In principle the electronic switches would be more reliable, since they would have no moving parts that would wear out, but the technology was still new at that time and the tubes were comparable to relays in reliability. Electronic components had one major benefit, however: they could ``open'' and ``close'' about 1,000 times faster than mechanical switches. The earliest attempt to build an electronic computer was by J. V. Atanasoff, a professor of physics and mathematics at Iowa State, in 1937. Atanasoff set out to build a machine that would help his graduate students solve systems of partial differential equations. By 1941 he and graduate student Clifford Berry had succeeded in building a machine that could solve 29 simultaneous equations with 29 unknowns. However, the machine was not programmable, and was more of an electronic calculator. A second early electronic machine was Colossus, designed by Alan Turing for the British military in 1943. This machine played an important role in breaking codes used by the German army in World War II. Turing's main contribution to the field of computer science was the idea of the Turing machine, a mathematical formalism widely used in the study of computable functions. The existence of Colossus was kept secret until long after the war ended, and the credit due to Turing and his colleagues for designing one of the first working electronic computers was slow in coming. The first general purpose programmable electronic computer was the Electronic Numerical Integrator and Computer (ENIAC), built by J. Presper Eckert and John V. Mauchly at the University of Pennsylvania. Work began in 1943, funded by the Army Ordnance Department, which needed a way to compute ballistics during World War II. The machine wasn't completed until 1945, but then it was used extensively for calculations during the design of the hydrogen bomb. By the time it was decommissioned in 1955 it had been used for research on the design of wind tunnels, random number generators, and weather prediction. Eckert, Mauchly, and John von Neumann, a consultant to the ENIAC project, began work on a new machine before ENIAC was finished. The main contribution of EDVAC, their new project, was the notion of a stored program. There is some controversy over who deserves the credit for this idea, but none over how important the idea was to the future of general purpose computers. ENIAC was controlled by a set of external switches and dials; to change the program required physically altering the settings on these controls. These controls also limited the speed of the internal electronic operations. Through the use of a memory that was large enough to hold both instructions and data, and using the program stored in memory to control the order of arithmetic operations, EDVAC was able to run orders of magnitude faster than ENIAC. By storing instructions in the same medium as data, designers could concentrate on improving the internal structure of the machine without worrying about matching it to the speed of an external control. Regardless of who deserves the credit for the stored program idea, the EDVAC project is significant as an example of the power of interdisciplinary projects that characterize modern computational science. By recognizing that functions, in the form of a sequence of instructions for a computer, can be encoded as numbers, the EDVAC group knew the instructions could be stored in the computer's memory along with numerical data. The notion of using numbers to represent functions was a key step used by Goedel in his incompleteness theorem in 1937, work which von Neumann, as a logician, was quite familiar with. Von Neumann's background in logic, combined with Eckert and Mauchly's electrical engineering skills, formed a very powerful interdisciplinary team. Software technology during this period was very primitive. The first programs were written out in machine code, i.e. programmers directly wrote down the numbers that corresponded to the instructions they wanted to store in memory. By the 1950s programmers were using a symbolic notation, known as assembly language, then hand-translating the symbolic notation into machine code. Later programs known as assemblers performed the translation task. As primitive as they were, these first electronic machines were quite useful in applied science and engineering. Atanasoff estimated that it would take eight hours to solve a set of equations with eight unknowns using a Marchant calculator, and 381 hours to solve 29 equations for 29 unknowns. The Atanasoff-Berry computer was able to complete the task in under an hour. The first problem run on the ENIAC, a numerical simulation used in the design of the hydrogen bomb, required 20 seconds, as opposed to forty hours using mechanical calculators. Eckert and Mauchly later developed what was arguably the first commercially successful computer, the UNIVAC; in 1952, 45 minutes after the polls closed and with 7% of the vote counted, UNIVAC predicted Eisenhower would defeat Stevenson with 438 electoral votes (he ended up with 442).

Personal Computer

A small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.A small, relatively inexpensive computer designed for an individual user. In price, personal computers range anywhere from a few hundred dollars to thousands of dollars. All are based on the microprocessor technology that enables manufacturers to put an entire CPU on one chip. Businesses use personal computers for word processing, accounting, desktop publishing, and for running spreadsheet and database management applications. At home, the most popular use for personal computers is for playing games. Personal computers first appeared in the late 1970s. One of the first and most popular personal computers was the Apple II, introduced in 1977 by Apple Computer. During the late 1970s and early 1980s, new models and competing operating systems seemed to appear daily. Then, in 1981, IBM entered the fray with its first personal computer, known as the IBM PC. The IBM PC quickly became the personal computer of choice, and most other personal computer manufacturers fell by the wayside. One of the few companies to survive IBM's onslaught was Apple Computer, which remains a major player in the personal computer marketplace. Other companies adjusted to IBM's dominance by building IBM clones, computers that were internally almost the same as the IBM PC, but that cost less. Because IBM clones used the same microprocessors as IBM PCs, they were capable of running the same software. Over the years, IBM has lost much of its influence in directing the evolution of PCs. Many of its innovations, such as the MCA expansion bus and the OS/2 operating system, have not been accepted by the industry or the marketplace. Today, the world of personal computers is basically divided between Apple Macintoshes and PCs. The principal characteristics of personal computers are that they are single-user systems and are based on microprocessors. However, although personal computers are designed as single-user systems, it is common to link them together to form a network. In terms of power, there is great variety. At the high end, the distinction between personal computers and workstations has faded. High-end models of the Macintosh and PC offer the same computing power and graphics capability as low-end workstations by Sun Microsystems, Hewlett-Packard, and DEC.