A laptop computer contains custom components selected and assembled by the vendor. Typically you cannot build or repair a laptop on your own. Desktop computers, however, are assembled from standard components. You can certainly build your own desktop out of components purchased separately, and you can usually fix or upgrade individual components with standard parts.
There are several different sized screws, but you can manage all of them with a single medium sized Phillips screwdriver. Everything that doesn’t screw in will just snap into place.
[For another description with pictures (but oriented to more powerful high-end systems), read this step by step guide from The Tech Report_.]_
The CPU comes from Intel or AMD. Every other part can be obtained from a half dozen different vendors. The parts all meet standards, so they all work together.
- The Case holds the mainboard, disks, and all the other parts. Typically cases are sized to match the mainboard you use (ITX for really small, MATX for small, ATX for standard, and EATX for unusually large), but “small form factor” (SFF) cases may also have a limitation of only “half-height” adapter cards that you plug into the mainboard. Some cases come with a Power Supply, but usually you buy one separately.
- The Power Supply is a metal box with cables that dangle from it and connect to devices inside the case. It is attached to the case with four screws one of which does not attach at a corner. This forces you to insert the box in the correct direction so the cooling fan on the side of the power supply points in the direction where the case will provide proper air flow. The cables all feed from the power supply into the case and attach to the mainboard, cards, and devices in the computer. the cables all plug into place by simply pushing them into or onto a socket.
- There is a rectangular hole in the back of the computer. Each mainboard comes with a small IO plate that adapts the large hole to specific smaller holes for the USB, video, and audio connectors on the back of the mainboard. Look at the mainboard to see how it goes, then plug it into place before you attach the mainboard. The computer will function without the plate, but that just allows one more hole to attract dust and screw up the air flow.
- The mainstream CPUs from Intel and AMD come with a fairly light cooler that will simply attach to the mainboard, but if you get a high performance CPU chip (an Intel “K” or AMD “X”) then you have to buy your own cooler. If you get a big air cooled heat sink, it can weight too much to attach to the board without more support, so there is a metal plate that you have to screw onto the back of the mainboard to support the weight of the cooler. If so, you want to attach that plate first before you mount the mainboard in the case.
- The case has a metal tray to support the mainboard, but the metal would short out circuits on the mainboard if they came into direct contact with the tray. So there are “standoffs” that stick up from the tray to keep the mainboard at least a quarter of an inch above the tray. First check the current location of the standoffs on the tray to the location of holes on the board and move the standoffs if necessary to match. Now set the board on the standoffs and push it toward the back of the case so the USB, video, and audio ports stick out properly through the holes in the IO plate installed in Step 3. Now you attach the board firmly with 6 or 9 screws that go through the holes on the mainboard and into the standoffs.
- The largest connector on the power supply has a 24 pins and plugs into a corresponding very large slot on the edge of the mainboard. There is a second connector to provide 12 volt power for just the CPU. Originally it had 4 pins, but then another 4 pins were added, so this connector can be an 8 pin plug or two 4 pin plugs side by side. Both the 24 and 8 pin connectors have a latch on one side of the plug connected to the cable and a small plastic tab on one side of the socket on the mainboard. You will get things plugged in correctly if you line up the latch to the tab. The pins have shapes. Most are rounded, but a few are square. Match the round and square pins to the round and square sockets on the mainboard if you have any doubt about the location of the latch and tab. Or to be careful, check both the latches and the pin shapes before plugging things in.
- The CPU chip has an arrow on one corner and the socket has an arrow on one corner. Match them up. The connectors on the back of the CPU have a pattern and can be matched to the same pattern in the socket. The CPU is latched in place with a clip, and then the cooler is mounted on the top.
- An Intel cooler attaches by pushing four mounts into holes in the motherboard and then turning them 90 degrees to latch them in place. An AMD cooler attaches by pushing a metal tab with a hole over a connector that sticks out on both sides of the socket and then pushing an arm that locks everything in place with some tension. Third party add on coolers may have custom mounts that screw into place.
- Plug memory into the memory slots. There is a notch in the memory that aligns with a tab in the socket. If they don’t go in at first, you may be trying to plug them in backwards.
- If you have a video card, plug it into the long PCI Express slot. There is a latch on the end of the slot to secure both ends of the card. However, those who do not play video games may be satisfied with built in video that comes with the CPU chip.
- The hard disk and DVD drive connect to the case with four screws, typically two screws on each side. These screws also come with the case, but they are slightly smaller than the screws that hold the mainboard to the standoffs. There are only the two sizes of screws.
- Plug the long thin SATA cable to first SATA socket on the mainboard and connect the other end to the back of the disk. There is an L shaped connector so it cannot go in wrong. Sometimes the SATA cable has a metal catch that snaps and holds the cable in place. Connect a SATA power cable from the power supply to the back of the disk.
- A case has a power on button, a reset button, and two LED lights for power on and disk activity. A bundle of cables will run from the front panel of the case to the mainboard. Unfortunately, there is no standard here, so all four cables have to be individually attached to the right set of pins on the mainboard. There will be a diagram on the mainboard instruction manual. The power and reset buttons have no orientation, but you can plug the two lights in backwards and then they do not work. So if you bring the computer up and the lights are off, turn it off and flip the direction of the corresponding connector. There may also be a connector for a speaker that goes “beep” once when you power on the machine. Really good mainboards built by vendors who care about these things will come with a separate adapter that allows you to connect the cables to the adapter outside the case where you can see what you are doing and then plug the adapter onto the mainboard rather than having to fiddle with the cables deep inside the case where it is very difficult to reach and see.
- Connect the monitor, keyboard, and mouse. Plug the power cable in the wall and turn the machine on. It is time to install an operating system.
The first time you do all this you may spend hours checking and rechecking everything. When you get used to it, the whole process can take as little as 20 minutes. On an assembly line, a worker probably builds a system in 3 minutes.