Megabyte(Mb) - A unit of data storage consisting of about one million bytes. This is normally used to refer to the amount of system memory or floppy disk storage.

Megahertz(Mhz) - A unit of frequency. It is one million hertz. It describes the clock frequency the microprocessor runs at. The larger the number, generally the faster the microprocessor, but there are other factors that affect microprocessor speed.

Gigabyte(Gb) - A unit of data storage consisting of about 1000 megabytes. This is normally used to refer to the amount of capacity a hard drive has.

RAM - Random Access Memory

Opening the case

Warning!!!   Before deciding to open your computer case and touch or remove any parts inside, you should be aware that your body can contain static electricity that may be discharged to the circuits inside your computer.  A static discharge can damage or ruin your computer.  Therefore while working on your machine you should always touch the frame of the machine and have one part of your body in contact with it at all times.  What you are trying to prevent is a charge of static electricity sparking between you and the parts you will be working on.  Especially when working with the microprocessor, memory, motherboard, or other plug in boards.

Warning! Hazard! Prior to opening your computer case, be sure it is turned off and unplugged.  110 volts can cause injury or death!  Working on your computer while it is plugged in can damage or destroy it.  Notice I said you can cause damage to the computer.  Unless you stick something metal into the power supply (there is nothing in there you need to worry about) you will not normally be harmed by the computer. If you are wearing metal rings, necklaces, bracelets, or have other things dangling in the machine you can damage it or hurt yourself.

Here is a good opportunity to be a good example for anyone (our little ones) watching us to teach them the proper way to work on electronics.

Besides you may need their help, if you get stuck and forget where a part went and have to take it out and put it in again.

To open the computer case, depending on the type of case you have, follow one of the these sets of instructions.

On some of our machines you press a clip under the front of the machine.

on others

Remove one or two phillips head screws from the back of your case that may hold one or more panels.

on others

Remove 4 or 5 screws in the back of the case. Be sure these screws hold the case and not some other component like the power supply.

Slide the case foreword on its slots and remove it.

Remove the top panel and/or one or more necessary side panels.

Once you have opened the case, lay it on its side so you can look at the inside components. You should see some variation of the following picture.

In the picture, the front of the computer is at the bottom and the rear is at the top. At the front (bottom of the picture) are normally two metal bays made to enclose hard drives, floppy drives, and CD-ROM drives. There is a 5.25 inch and a 3.5 inch set of bays. Most hard drives will mount into the smaller 3.5 inch bays with the CD-ROMS mounting in the 5.25 inch bays. The hard floppy, and CD-ROM drives are mounted to their enclosures with screws on their left and right sides. The power supply is on the top right side of the picture which when the computer is in its normal position is the top rear.

Cables
Between the hard, floppy, and CD-ROM drive bays you will see some thin flat gray cables going to the floppy and hard drive connectors on the motherboard. These are data cables used by the system to control the drives and get and send data from and to them.  On one side of the gray cable should be a stripe (red or blue or a different color) going along the cable. This stripe should always be placed on the pin 1 side of the connector. You will need to look closely at the connectors on your hard and floppy drives to determine which is the pin 1 side or read your manual. On hard drives and most CD-ROMs pin 1 is on the side closest to the power supply connector.  Some of the data cables are keyed, so they are aren't put in backwards but others are not. It varies a little from system to system.

Cables running between the power supply are colored black, red, and yellow. There is one going to each hard drive, floppy drive, CD-ROM drive and any other drive the system is using such as a mass storage device. In most of the machines the the power connector for the floppy drives is smaller than the ones for the hard drive or the cd-roms. There is also a multicolored power supply cable with about 12 wires going between the power supply and the motherboard. The wires are colored black, red, yellow, orange, and blue this varies. The connector on this cable should be keyed so it cannot be inserted the wrong way

The Memory Slots
The motherboard holds the microprocessor, the memory, and several card slots.  Most boards have 2, 3, or 4 memory slots, which may, depending on the size used, allow up or beyond 1 Gb total system memory.

The Card Slots
The card slots are used to put additional cards such as video cards, sound cards, internal modems, or network cards into. Some motherboards today include video, network, and sound without the addition of a extra card. These cards slots today are mostly PCI type card slots. When talking about cards that are plugged into a PC you are talking about the expansion bus. The expansion bus is a means of a microprocessor extending its communication ability further into the outside world. It is a data exchange  between add on cards and the microprocessor and the motherboard. There have been several types of expansion buses.

ISA - Industry Standard Architecture. Used when the original 8088 8bit microprocessor based personal computers were produced..

PCI - Peripheral Component Interconnect. The popular expansion bus of choice. It is significantly faster than EISA.

AGP - Accelerated Graphics Port. This bus is developed for fast video cards.

The current popular expansion bus is the PCI (Peripheral Component Interconnect) bus for all cards except the graphics cards. For graphics cards, the bus of choice is AGP. Most motherboards today have one AGP slot and several PCI slots and some ISA slots.  The ISA slots are larger than the PCI ones.   ISA slots are slower than PCI so if possible use PCI expansion cards.  Your expansion cards will plug into these card slots. Be sure you get cards that match the available type of slots on your motherboard.

Some microprocessor runs at 500Mhz and my memory runs at 100Mhz. Why?
As PC technology grew, eventually the access speed of the memory could no longer keep pace with the increased speed of the microprocessors. At this point, an I/O cache was placed on the microprocessor to be a buffer between the external memory on the motherboard and the internal processor registers. The memory was set to run at a different "side bus" speed which is some fraction of the microprocessor speed. Therefore when the speed of the microprocessor is set, it is set to some multiple of the side bus speed. In the case of a 500Mhz processor and 100Mhz PC100 capable memory, that multiple is 5. Sometimes this multiple and the sidebus frequency is set using jumpers on the motherboard, or it may be set with auto detection and the BIOS.

Chipset and BIOS
One issue that will affect the operation of the motherboard is the chipset it uses and its BIOS it uses. The chipset is used to control the interface between the microprocessor and most of the devices and memory on the computer. The chipset used can have a significant affect on the performance of your system as can the overall design of the motherboard.

Your system's BIOS is a computer program that allows your system to begin running and provides a small library of functions that your system will use to interface to various devices such as your hard drive, keyboard, mouse and other items.  The BIOS resides in a chip on the motherboard called a ROM chip. Usually part of this ROM can be reset or re programmed with updates. ROM that can be electrically re-written this way is called "flash" ROM.

The Microprocessor

The microprocessor is the brain of your computer. It processes instructions and communicates with outside devices, controlling most of the operation of the computer. The microprocessor usually has a large heat sink attached to it. Some microprocessors come in a package with a heat sink and a fan included as a part of the package.

Microprocessors and Mounting
The mounting method refers to the type of connection the microprocessor makes with the motherboard. The following table lists the various mounting packages and some of the well known microprocessors that are mounted for that package.

Socket 7 - AMD K5, K6, Intel Pentium 75-200Mhz, IBM
Socket 370 - Some Intel Celerons
Slot 1 - Intel Pentium II, Pentium III, Some Celeron 266-533
Slot II - Intel Xeon
Slot A - AMD Athlon

The Memory

Packaging
Memory chips are called DIPs which stands for Dual Inline Packages. They are black chips with pins on both sides. Some say they look like black bugs. To make memory installation easier than it was in the past, these DIP chips were places on modules. There are two main module types that memory comes packaged on today.

SIMM - Single Inline Memory Module. They may have DIPs on one or both sides and will have 30 or 72 pins. Today, they normally are available in the 72 pin size which supports a 32 bit data transfer between the microprocessor and the memory.

DIMM - Double Inline Memory Module. The modules have 168 pins and support a 64 bit data transfer between the microprocessor and the memory. Synchronous Dynamic Access Memory (SDRAM) is the type of memory that is found on DIMM packages. The term SDRAM describes the memory type, and the term DIMM describes the package. These modules are available in 3.3 or 5 volt types and buffered or unbuffered memory. This allows four choices of DIMM types. You should check your motherboard manual to determine the type of memory required.

To install these packages, you press them into the socket on the motherboard and latch them in with a plastic latch on both sides. Normally as the memory module is pressed into place the latch will automatically latch the module in place.

DRAM Access
DRAM memory is is accessed in chunks called cells. Every cell contains a certain number of bits or bytes. A row, column scheme is used to specify the section being accessed. The cells are arranged similar to the following table.

ROW 1, COL 1    ROW 1, COL 2     ROW 1, COL 3    ROW 1, COL 4

ROW 2, COL 1    ROW 2, COL 2    ROW 2, COL 3    ROW 2, COL 4

ROW 3, COL 1    ROW 3, COL 2    ROW 3, COL 3    ROW 3, COL 4

ROW 4, COL 1    ROW 4, COL 2    ROW 4, COL 3    ROW 4, COL 4

When the DRAM is accessed, the row, then the column address is specified. A page in memory is considered to be the memory available in the row.

Types of DRAM
The term DRAM stands for Dynamic Random Access Memory. There are three common types of DRAM today.

FPM DRAM - Fast Page Mode DRAM. When the first memory access is done, the row or page of the memory is specified. Once this is done, FPO DRAM allows any other row of memory to be accessed without specifying the row number. This speeds up access time.

EDO DRAM - Extended Data Out DRAM. This works like FPO DRAM but it holds the data valid even after strobe signals have gone inactive. This allows the microprocessor to request memory, and it does not need to wait for the memory to become valid. It can do other tasking, then come back later to get the data.

SDRAM - Synchronized DRAM inputs and outputs its data synchronized to a clock that runs at some fraction of the microprocessor speed. SDRAM is the fastest of these three types of DRAM. There is a new SDRAM called DDR (Double Data Rate) SDRAM which allows data reads on both the rising and falling edge of the synchronized clock.

Cache Memory
Cache memory is special memory that operates much faster than SDRAM memory. It is also more expensive. It would be impractical to use this memory for the entire system both for reasons of expense and physical board and bus channel design requirements. Cache memory lies between the microprocessor and the system RAM. It is used as a buffer to reduce the time of memory access. There are two levels to this memory called L1 (level 1) and L2 (level 2). The level 1 memory is a part of the microprocessor, and the level 2 memory is just outside the microprocessor.

The Hard Drive(s)

Construction
Hard drives consist of a series of round metal plates called platters, also called cylinders. They are coated with an electromagnetic material which can support magnetic states that are capable of being electrically altered. This means some type of electrical signal can alter the magnetic polarization of various areas of the plates. The state of these polarized areas can also be sensed. Each platter can hold large amounts of data. There are several platters mounted on a hard drive. Between each platter is a head which is used to sense and modify the states of the platter. There are two heads on each platter.

Each platter has data stored on it in a specific pattern for read and write access. The data is organized into tracks which are rings around the platter. The distance the head moves into the platter will determine which track is read. A sector is a section of data in the cylinder. Different hard drives have different numbers of sectors, tracks, and platters.

Controller Interface Types
A hard drive is a mass storage device where your operation system is installed along with many data files. There are two types of hard drives with regard to the controller:

IDE - Integrated Drive Electronics. A controller based interface. If your primary concern is low price with reasonable performance IDE is a good choice. It is still the most popular controller interface because of price.

SCSI - SCSI uses a separate bus hooked to the system bus using a host adapter. It is a more expensive system than IDE, but is better built and has a great deal of flexibility.  There are several types of SCSI interfaces, the primary difference being the width of the data transfer (how many data bits are carried over the cable at a time). The important item is to be sure you get compatible controllers with your SCSI device such as your hard drive or CD-ROM drive.

Most hard drives have three characteristics of main importance for performance.

Size - The size of the hard drive is expressed in terms of Gigabytes which is roughly 1000 Megabytes.

Speed - The data output of a hard drive is primary limited by the amount of time it takes for the electromagnetic head to reach the data at specific locations on the drive. The primary factor of limitation is hard drive rotation speed.

Reliability - The other performance factor that is worth considering is reliability. This is expressed as mean time between failure (MTBF) The higher the number, the better. Look for this specification on the manufacturer's specification sheets for each product.

The CD-ROM

Originally CD-ROMS were read only devices, but now read/write technology has been developed.

Interface
Many CD-ROMs are interface to the computer using the ATAPI interface. This is ATA Packet Interface which is a IDE interface. This is designed for extra drives like CD-ROM's and tape drives that connect to an ATA connector. The ATAPI interface is the standard interface for IDE controlled CD-ROMS. If your CD-ROM uses an a ATAPI interface, it should be supported by all available software. If you are using a SCSI controller, you should probably use a SCSI CD-ROM. There are two primary types of CD-ROMs today.

Speed
The primary performance concern of CD-ROM drives is their speed. Speeds are expressed in terms of 1X, 2X, 4X, which is the number of times the drive is than the standard CD-ROM reader. Of the read only type, speeds have exceeded 50X.

The read/write type of CD-ROM speeds are expressed with three values. They are read, write, and rewrite. Speeds of some of these devices are read at 32X, write at 10X, and rewrite at 40X.

Other storage devices include:
DVD Drive - DVD stands for Digital Video Disk. Most DVD drives use the ATAPI interface. They are available as internal or external devices. They are primarily used for video storage but they can be used to hold audio and computer data. DVD is categorized into DVD-Video and DVD-ROM devices. The DVD-ROM device is for computer data storage.

Zip drives - A removable cartridge storage device that may be used to store compressed data as a data back up method. A zip drive has between a 100Mb to 2G storage capacity. Cost is usually between $45 and $350.

More about DVD-ROM

There are five recordable versions of DVD-ROM. They can all can read DVD-ROM and DVD-Video discs, but different type of disc is used by each one for recording.

DVD-R/authoring - Can record data once.

DVD-R/general, - Can record data once. The capacity is 3.95 Gb or 4.7 Gb.

DVD-RAM - It is not compatible with current drives. It has a storage capacity of 2.58 Gb It can be rewritten about 100,000 times The discs are expected to hold data for 30 years or more.

DVD-RW - The capacity is 4.7 Gb. It can be rewritten about 1,000 times.

Monitors are used to view your data on a computer. The characteristics of your monitor are very important for your system performance since the quality of your video will significantly affect your computing experience.

Components
Most monitors today consist of a picture tube and electronic control circuitry which are used to transfer the signal to the screen. There are some monitors that do not use a picture tube, but use electronics to display information. These monitors are call flat screens and are more expensive than regular monitors.

The primary and most expensive component in a standard monitor is its picture tube. The most important characteristics of a monitor generally refer to picture tube specifications although other circuitry can also be important in providing picture clarity. A picture tube is basically a large vacuum tube with a phosphorescent coating on the front of it. At the back of the picture tube is a large electron gun ( actually 3 guns ) which shoot(s) electrons onto the phosphorescent coating at the front of the tube. When the electrons strike the coating, the coating glows. The coating provides the primary colors which are red, blue, and green. These component colors and their combinations can be used to make every other possible color combination. There is other circuitry which works with the gun to direct the electron gun to the proper color at the correct time, and to direct the gun to the correct location on the screen depending on the phase of the video signal that is being sent to the monitor. There is magnetic circuitry which is used to bend the electron beam to strike the appropriate area on the screen. This is referred to as deflection.

The yoke is an electromagnetic coil used to guide the beam to its intended location. The color pattern on the phosphorous appears like the three colored circles shown on the left side of the drawing below. There are many of these color patterns on the screen. The closer the groups of these three patterns are, the better the resolution of the monitor can be. Monitor resolutions refers to the number of lines per inch that can be seen on the screen. It is rated in vertical (up and down the screen) and horizontal (left and right) terms.

Important Specifications

Some of the most important specifications on the monitor are:

Screen size - Expressed in inches, it is the approximate size of the picture tube when measured from the lower left corner to the upper right corner.

Spacing - Expressed in dot pitch. This is the description of how close the three color patterns are spaced apart in the screen. The smaller number, the better.

Maximum resolution at a specific frequency. This refers to the amount of pixel resolution viewable on the screen at a specific scan frequency. The higher the pixel resolution at a higher given scan frequency, the better the monitor is. Generally look for 17 or 18 inch monitors that will support at least 1024 x 768 pixel video resolution at 80Hz.

How dot pitch spacing can be deceiving

Different manufacturers and vendors rate dot pitch different ways. There are actually three characteristics of dot pitch. They are:

Horizontal

Vertical

Diagonal

As you can see depending on how the dot pitch is measured, you may get different numbers. You will need to carefully check manufacturer's specifications to be sure the monitor you buy has the spacing you think it has.  Also read reviews on the monitors to see which ones have the best performance.

If you would really like to get any use on your computer, you would probably like a keyboard and a mouse.

Keyboard
Keyboards can range in cost from about $10 to $100. I generally stay with less expensive keyboards.  There are keyboards with a different feel or sound when key pressing is done. Some people are particular about the feel and sound. If you are, you may want to spend a little more for your keyboard. You may even want to buy it from a retail store so you can test the feel of it. There are special keyboards with extra functions on them for such things as surfing the internet.

Mouse also called Pointing devices
The pointing device interface of choice is the PS/2 or the USB interface rather than the older serial interface. Using a one of these interfaces will not require the use of a serial port on your computer.

There are a quite a few types of pointing devices available. The main choices are between:

Two or three buttons mice

Trackballs

Wireless 

The choice of pointing devices depends on your preference and whether the software you run on your computer will support it. If it does not support it, it just means that you will not be able to use some of the features on the pointing device. Many mice today have a sprocket wheel in the center which will allow the user to scroll up and down documents on the screen by turning the wheel. Also some mice are "ergonomic".

Depending on features and the quality of the internal roller ball and mechanisms, a mouse can cost anywhere from $2 to $100. Or possibly you can find one in your back yard, basement or a yard sale for free or foe a low cost.

Below is a list of advantages and disadvantages of building your own system.

Advantages:
I believe there is some price break in buying component parts through discount dealers locally or on the web.

When you buy from some retail stores or buy a complete system, you do not get to choose your own parts. In many cases, you may get a lower quality motherboard, monitor, CD-ROM or other parts. When buying your own parts you choose the best quality and features of parts for the money.

Disadvantages:
There is no dealer to stand behind the computer with a warranty or service agreement if something goes wrong.

You have to put it together yourself and install your operating system which can take several hours.

You must do more research, but that can be part of the fun.

Please be aware that a disadvantage listed above is there is no dealer warranty. If you purchase a name brand quality computer component, however, and it is installed properly, there is a manufacturer's warranty. Depending on the product, it may be anywhere from 30 days to 3 years. Another thing to consider is that many vendors have what are called "bare bones" systems that you can buy the motherboard, with the microprocessor, and memory already assembled, then you can buy your own video, sound, and other cards along with hard drive and add it to your system. Also you can buy your monitor separately from your main system and still get a quality monitor of your choice.

What is OEM?

OEM stands for original equipment manufacturer. When you buy an OEM part, it means you may not get any manuals, or software that accompanies the product in a retail box. An OEM part is shipped as though it is sent to a dealer who already knows how to install it and who would have the software to install it. This may be significant depending on the part you are purchasing. If you are purchasing a hard drive, floppy drive, or CD-ROM drive it is not a serious concern. In this case it is better to get the price break. If you buy an OEM disk drive, you can always get installation instructions and any necessary drivers from the the service and support section of the manufacturer's website.

If you are buying a sound card or video card, you may or may not want to make your purchase an OEM purchase. For instance there may be special software with a sound card that lets you write your own music. If this is the case and you want the software, you should make the retail package purchase. Also some video cards come with special game or other software packages. In the case of a sound card or video card, buying OEM software is a matter of preference.

When buying a microprocessor, always choose to buy a retail package. This is because a retail package will come with any required hardware such as a fan and heatsink. The warranty and return policy is also better. You may choose to save money and buy the OEM package if you are confident that you won't have any problems with your microprocessor.

Other items not listed above such as a motherboard have always come with a manual and associated hardware so there is not an an issue of buying OEM. The monitor is also sold as a standard package. The mouse, keyboard and CD-ROM also do not discriminate between OEM and retail packages.