Let's assume you need a desktop PC, perhaps one that your family uses for entertainment and surfing and email, or one that is a serious business or engineering machine. It could be that this is not you, that for your needs, laptops, tablets, and phones suffice. But let's assume you need a desktop. It's not that hard to build one from parts. The only tool you'll need is a screwdriver. Your first one will take some time though, shopping for components, then methodically putting the pieces together. It will save you some money and teach you a bit about what it means to be a computer. And you can customize it just the way you like. You'll grow a little geekier along the way, and feel more self-sufficient. If anything ever goes wrong you'll have a better clue about how you might fix it yourself too.

How to kick the tires first

Open the case of any unused old desktop computer and look inside; figure out what the “motherboard” is, where the CPU ought to be on the motherboard (often concealed underneath a cooling fan), the “power supply” (where lots of cables emanate from), and the hard drive(s) or CD/DVD drive(s). If you can identify all these parts then you have enough of a conceptual model to build a computer.

Recycle what you already own

One approach is to start with your abandoned old hardware and just upgrade some or maybe most of the components. Unless the machine is more than, say, 7 or 8 years old, the case is probably just fine. Recent cases have USB and audio ports in the front, so those are a sign that the case will be upgrade friendly. The older the machine, the more of its components you're likely to want to replace. But a decent case and the power supply inside will save you a few bucks no matter what. As an example, my most recent upgrade was on a computer I had built 3 years previously. The case and power supply were fine, but I wanted a little more oomph so I replaced the motherboard, the CPU, and the memory (RAM). The optical drive (DVD and CD) and hard drive were also fine. All the new parts together came to $150, but I put the leftovers into an even older case and sold that rebuilt computer on Craigslist for $55 (a bargain -- swamped with would-be buyers at that price), so the net out of pocket cost for the upgrade was $95.

Or, start from scratch

The other approach is to start from scratch. One of the sources I use is Newegg (whether upgrading or starting from scratch), but there's plenty of competition out there. And actually, Newegg will help walk you through the process here, but you can also Google other tutorials for do-it-yourself (DIY) computers.

What a desktop PC consists of

Regardless of the approach you take, this is everything essential that goes into a home computer, whether it's worth $50 or $5000:

• A case
• A power supply. Often this is included when you buy or inherit a case, and they are generally more convenient and cheaper together.
• A motherboard
• A CPU
• A cooling fan for the CPU. Sometimes this comes with the CPU, in which case you don't have to buy a separate one.
• Memory (RAM)
• A hard drive (spinning) or solid state drive (SSD). SSDs are much faster but more costly.
• An optical drive, meaning a DVD or CD or Blu-ray drive. (A minimalist could argue that this is not absolutely essential, but it's such a practical item that you should have one.)

And that's it.

Upgrading an existing computer

It follows that a minimalist DIY upgrade to a newer computer might be to simply increase RAM, or put in a more powerful CPU (with cooling fan). You don't even need a screwdriver for either of these upgrades, except possibly to open up the case.

Repairing a broken computer

A pretty straightforward repair to a "broken" computer might entail replacing the power supply. Or replacing the hard drive.  Either of these repairs amounts to merely detaching some cables, using a screwdriver to replace the old unit with a new one, and re-attaching the cables.

Peripherals

In addition, but distinct from the PC unit itself, you'll need a mouse and keyboard and monitor. All the other bells and whistles you see in marketing brochures are either going to be onboard -- built in to the motherboard -- or embellishments you can acquire separately. Onboard examples you get automatically are:

• USB ports
• Video port(s)
• Audio ports for microphone, speakers, headphones

Software

Finally, when you're done, you'll need some software, starting with an operating system. You can install Windows if you have a license. Or you can try out Linux.

--- Updated 19 September 2012