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How to Build a PC

A breakdown of the technology and pieces used to build a personal computer.

The first thing a computer needs is the motherboard, a square or oblong shaped circuit board that controls all components of the computer. This is the basis of the computer and provides connections for all other devices. Located on the motherboard is a large microchip called the Central Processing Unit (CPU). This computer chip acts as the brain of the system and calculates billions of instructions sent to it from all other devices. When someone refers to their computer in terms of megahertz or gigahertz, this references the speed at which the CPU can process instructions. The higher the number, the faster the computer can perform a given task.

Motherboard connections to other components. If a component does not connect to the motherboard in some manner, it is not part of the computer. Every piece of the computer connects to the motherboard, even the printer. Here is a look at the different interface connections on a motherboard and what they are used for.

Power Connection • The motherboard draws power from the power supply inside the case. The power connection is a unique (usually white) plug on the back corner of the motherboard. Although only one cable from the power supply will fit this connection it is still important to make sure the power is plugged in correctly or damage to your equipment may result. Older motherboards use two power cables sitting side by side.

Serial and Parallel Ports • Next to the power connection on the motherboard are several groups of pins. At a closer look they are labeled Serial 1, Serial 2, Parallel 1, and Parallel 2. The serial connections have 9 pins each while the parallel connections have 25. The motherboard comes with cables that will plug into these connections. One end of the cable is plugged into the motherboard and the other end screws into the back of the case. This provides connection points for a mouse, printer, or other serial and parallel devices.

IDE Controllers • The majority of motherboards available have two IDE controllers. The CPU communicates with devices like a hard drive, floppy drive, and CD-ROM drive through the IDE controllers on the motherboard. There are two rows of 20 pins sticking out of the motherboard for each IDE controller connection (Primary and Secondary Controller). A flat 40-pin cable is connected from the IDE connection on the motherboard to an IDE compatible component. Up to two devices can be connected to each IDE controller. A hard drive should be connected to the primary IDE connection while most CD-ROM drives are connected to the secondary connection.

Floppy Drive Controller • Located next to the IDE controllers on the motherboard is the floppy drive controller. This connection consists of two rows of 17 pins and a flat 34-pin cable connects the controller to a floppy disk drive. Up to two devices can be connected to each floppy drive controller. Other components such as a tape backup drive can also be connected to the controller.

RAM expansion slots • Random Access Memory, or RAM, are microchips used to store program information. RAM will only store information when the computer is on and will lose all data when the computer is turned off. Between two and eight RAM expansion slots are found on most motherboards. The computer must have some RAM to startup correctly.

ROM • Although ROM cannot be changed on the motherboard, it is important to mention it here. ROM stands for Read Only Memory and consists of microchips on the motherboard that store information about the computer.

ISA, EISA, PCI, and AGP expansion slots • Internal components like a modem, video card, sound card, and Ethernet card use one of these expansion slots to connect to the motherboard. The slots can be located by looking for raised plastic connections on the motherboard near the back. These connections are parallel to each other and hard to miss. ISA and EISA expansion slots are no longer used on some motherboards while PCI and AGP slots have taken over in speed and popularity. Even so, ISA and EISA devices are still used.

Peripheral connections • All motherboards have the serial and parallel connections for devices like a mouse or printer. But there are other connections that are often integrated on the motherboard. They are easy to spot because the peripheral connections are just plugs on the back of the motherboard waiting for a cable to be connected. These connections are used for devices like a keyboard or mouse, and sometimes a monitor or sound card. Note that devices like the video card and sound card can be integrated on the motherboard or built into expansion cards that plug into ISA, EISA, PCI, or AGP expansion slots.

Now that we know all the connections on the motherboard, the components can be connected together. Please note that computer components are sensitive to static electricity. A cheap wrist strap should be purchased to ground you to the metal case and prevent damage to the computer parts.

We start with a computer case and power supply. The case and power supply are normally sold together and can be found at any computer parts store. The power supply needs enough voltage to run all your drives. So if you have extra devices, we recommend buying a higher voltage power supply.

Before the motherboard is in the computer case, make sure that the CPU and RAM are installed. Most CPUs are sold pre-installed with the motherboard. RAM comes separately and easily snaps into place in the RAM expansion slots.

After the CPU and RAM are installed, the motherboard mounts against a metal surface inside the case. Be sure to read your motherboard’s instructions on how to mount it correctly. The peripheral connections and plastic expansion slots should line up with slots on the back of the case. The motherboard screws into the case with several screws and plastic dividers.

Next the small serial and parallel cables are screwed into the back of the case and connected to their appropriate locations on the motherboard.

IDE and floppy disk drives should be installed next. This includes the hard drive, CD-ROM, and floppy drive. The front part of the case should have metal racks to hold these devices. Sometimes the metal rack to hold the hard drive is located in the back of the case. All you have to do is slide the device into it’s appropriate rack then put two screws in the holes on the side to keep it in place. It is easier to connect the IDE or floppy drive cable to these devices before installing them in the computer.

A note about connecting the cables

One edge of the cable will have a red stripe or dotted line down the side. This is pin 1 for the cable and must be connected to pin 1 on the motherboard and on the device. You can tell which pin is the first one by looking closely at the connection. The first and second pins are numbered next to the pins. This tells you which side of the controller connection the red line should be on when the cable is connected.

Floppy drive cable • The floppy drive cable has three plastic connections on it. One at each end and one close to one end. Between the two closest connections, there are several wires that are twisted 180 degrees before entering the end connection. This is so the computer can distinguish between two devices connected to a single cable. The end farthest away from the other connections plugs into the motherboard. The other end of the cable plugs into a device the computer recognizes as drive A while the middle connection plugs into drive B.

IDE cables • The hard drive cable is similar to the floppy drive cable in how it connects to IDE devices. The IDE cable also has a red line to denote pin 1 and it has 3 connections as well. The two closest connections plug into the master and slave IDE devices and the connection on the far end of the cable plugs into the motherboard. The other end connection is for a master IDE device such as a primary hard drive and the middle connection is for a slave IDE device such as a CD-ROM drive or second hard drive. Remember that the primary IDE controller on the motherboard should be connected to the main hard drive and that other IDE devices can be connected to the primary or secondary IDE controller.

A note about jumpers on IDE devices

Hard drives and CD-ROM drives have several pins with one or two jumpers on them. These pins are located next to the cable pins and are used to set the device to either master or slave. Look at how to connect the IDE cables above to decide if each device is the master or slave on that controller. The main hard drive should be set as the master device on the primary controller. There should be a diagram or writing on the IDE device to tell you which pins the jumper is placed on for each setting. Most devices can be set to master, slave, single drive, or cable select. Single drive means there is only one drive connected to the cable so the device is set to master. Cable select means the device is set to master if it is connected to the end of the IDE cable or it is set to slave if it is connected to the middle connection.

Now that we are done connecting the IDE and floppy drive components, we can move on to expansion cards. This may include the video and sound cards as well as an internal modem or network card. Remember that the expansion slots are raised plastic connections near the back edge of the motherboard. ISA and EISA connections are usually black in color and located near the side of the motherboard, closest to the edge. PCI connections are white in color and are next to the ISA and EISA expansion slots (If your motherboard has ISA and EISA slots). Next to the PCI connections are the AGP expansion slots. The AGP slots are light brown in color and sit further away from the back of the motherboard than the ISA, EISA, and PCI slots do.

Each expansion card must be inserted into its appropriate expansion slot then held in place with a screw at the back of the case. Again, devices like the video and sound cards can also be integrated into the motherboard.

Next we need to connect the remaining wires on the computer case to the motherboard. This includes the power and reset buttons and depending on your case, an internal speaker or other small input/output devices like an LCD or USB connections. There will be wires coming from the front of the case that have plastic connectors on the end. Written on these plastic connectors is what device that wire connects to. The corresponding pins are located on the motherboard, usually near the edge and are grouped together. Each group of pins should be labeled with what device it controls. If the motherboard is not labeled, the information can be found in the motherboard’s manual. Each set of wires from the case should be connected to its corresponding pins on the motherboard.

It’s time for power. There are many power cables coming from the power supply. Each goes to power the motherboard or a device like a hard drive. Start by connecting the power supply cable for the motherboard. Then power to the CD-ROM and hard drive can be connected. Note that the power cables for extra devices have four wires and will only connect to the device in one way. The power cable for the floppy drive can be connected next. This cable has a small plastic connection on the end and will only connect to the floppy drive in one way.

We can finally put the cover back on the computer case and connect a monitor, mouse and keyboard to see our computer come to life. And there you have it, we built a computer. Of course, an operating system needs to be installed on the hard drive before the computer is of much use.



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