The essential parts: what goes inside the case

Building a computer means buying individual components and connecting them together. You need five things that do the actual work: a motherboard (the main circuit board everything plugs into), a CPU or processor (the chip that runs calculations), RAM or memory (temporary storage the CPU uses while working), a storage drive (where your files and operating system live permanently), and a power supply (the box that converts wall power into the right voltage for each part).

You also need a case — the metal box that holds everything and protects it from dust and damage. Most cases come with fans already installed, but you may need to add more depending on how much heat your CPU and graphics card produce. If you want to display video on a monitor, you need a graphics card (also called a GPU), though many modern CPUs have graphics built in and don't require a separate card.

That's the core: motherboard, CPU, RAM, storage, power supply, case, and optionally a graphics card. Everything else is either cooling, cable management, or extra features.

Key Takeaways

  • A working computer needs a motherboard, CPU, RAM, storage drive, power supply, and case — these five parts are non-negotiable.
  • A graphics card is only necessary if your CPU doesn't have built-in graphics or if you plan to game or do video work.
  • The motherboard, CPU, and RAM must be compatible with each other — a CPU for one socket type won't fit a motherboard designed for a different socket.
  • The power supply wattage must be high enough for your CPU and graphics card combined, plus a safety margin of 20 to 30 percent.
  • You'll need a Phillips screwdriver, thermal paste (usually pre-applied to CPU coolers), and about two to four hours for your first build.

Motherboard, CPU, and RAM compatibility

The motherboard is where everything connects, and it only accepts a CPU designed for its socket — the physical slot where the processor sits. Intel and AMD make different CPUs, and even within each brand, older and newer generations use different sockets. Before you buy a CPU, check the motherboard's manual or product page to see which socket it has, then buy a CPU that matches that socket.

RAM also has to match the motherboard. Modern boards use DDR5 or DDR4 memory (the generation), and the motherboard manual will tell you which one it accepts. You can usually install two, four, or more RAM sticks depending on how many slots the board has. Most people start with 16 gigabytes (GB) of RAM — two 8 GB sticks — which is enough for gaming, web browsing, and most office work.

Check the motherboard's manual before buying anything. It lists the compatible CPUs, the RAM type and maximum capacity, the power connectors the power supply needs to plug into, and which storage drives it can connect to. Spending ten minutes reading the manual prevents buying parts that don't fit together.

Storage: SSD vs. hard drive

A solid-state drive (SSD) is the standard choice now. It has no moving parts, is much faster than an older hard drive, and costs less per gigabyte than it did five years ago. A 1 terabyte (TB) SSD is a good size for most people — enough for Windows or Linux, your programs, and hundreds of games or thousands of documents. If you need more space, you can add a second drive later.

SSDs connect to the motherboard using either an M.2 slot (a thin rectangular connector) or a 2.5-inch SATA port (an older, wider connector). Check your motherboard manual to see which slots it has. Most modern boards have at least one M.2 slot, and M.2 drives are faster, so that's the better choice if your board supports it.

A hard drive is cheaper per terabyte if you need massive storage — video editors or people with huge game libraries sometimes add a second hard drive for bulk storage — but for your main drive, an SSD is faster and more reliable.

Power supply: wattage and efficiency

The power supply converts electricity from your wall outlet into the right voltage for each component. You need to know the total power draw of your CPU and graphics card, then buy a power supply rated for at least 20 to 30 percent more than that.

A CPU alone typically draws 65 to 125 watts. A graphics card can draw anywhere from 0 watts (if you're using the CPU's built-in graphics) to 450 watts for high-end gaming cards. Add them together, add 20 to 30 percent as a safety margin, and that's your minimum power supply size. If your CPU draws 105 watts and your graphics card draws 320 watts, you need a power supply rated for at least 510 watts (425 × 1.2).

Look for a power supply with an 80+ Bronze rating or higher — that means it converts wall power to computer power efficiently, wasting less energy as heat. Brands like Corsair, Seasonic, and EVGA make reliable supplies. Avoid the cheapest no-name supplies; a failed power supply can damage other parts.

CPU cooling: stock coolers vs. aftermarket

Most CPUs come with a stock cooler — a fan and heatsink already attached or included in the box. For everyday use, gaming, and office work, the stock cooler is usually enough. It's free, it fits in most cases, and it does the job.

An aftermarket cooler is a third-party replacement that cools better or runs quieter. People upgrade to an aftermarket cooler if the stock cooler is too loud, if they're overclocking (running the CPU faster than its rated speed), or if their case is small and the stock cooler doesn't fit. For a first build, use the stock cooler and upgrade later if you need to.

Thermal paste goes between the CPU and the cooler to transfer heat. Most stock coolers come with paste pre-applied, so you don't need to buy any. If you buy an aftermarket cooler without paste included, you'll need a small tube — it costs a few dollars and lasts for many builds.

Case airflow and cable management

The case holds everything and protects it from dust. Most cases come with one or two fans already installed. If your CPU and graphics card don't produce much heat, that's usually enough. If you have a high-power graphics card or you're overclocking, you may want to add more fans — cases typically have room for two to four additional fans.

Fans pull cool air in from the front and push hot air out the back and top. You don't need to buy expensive RGB fans with lights; plain fans work just as well and cost less. A case with good cable management — space behind the motherboard tray to hide cables — makes building easier and improves airflow.

Size matters: a full-size ATX case fits full-size motherboards and has plenty of room to work. A smaller Micro-ATX case is more compact but tighter to build in. If you're building for the first time, a full-size case is more forgiving.

Optional: monitor, keyboard, and peripherals

The computer itself doesn't include a monitor, keyboard, or mouse — you buy those separately. A basic 1080p monitor costs $100 to $200. A keyboard and mouse can be cheap or expensive depending on what you want; a basic wired set costs $20 to $40.

If your graphics card or CPU has video output (HDMI, DisplayPort, or USB-C), you can plug a monitor directly in. If you're using an older graphics card or a very old CPU without built-in graphics, check what video connectors it has and make sure your monitor supports that connector type.

Tools and supplies you'll need

You need a Phillips head screwdriver — the kind with a + shape. Most of the screws in a computer are Phillips. An anti-static wrist strap is optional but cheap (a few dollars) and prevents accidental static discharge from damaging parts. You can also just touch the metal case occasionally to discharge static.

Thermal paste comes pre-applied on most stock coolers, so you probably won't need to buy any for your first build. A flashlight or headlamp helps you see inside the case. Set aside two to four hours for your first build — it's not hard, but it's not fast either.

Frequently Asked Questions

Do I need to install an operating system myself?

Yes. Windows, Linux, and macOS don't come pre-installed on parts you buy separately. You'll read Windows or Linux onto a USB drive on another computer, plug that USB drive into your new computer, and run the installer. Windows costs money (around $100 to $200 for a full license); Linux is free.

What if I buy parts that don't fit together?

Most online retailers and physical stores accept returns within 30 days if the parts are unopened. Before you open anything, double-check the motherboard manual against every part you bought. If you do open a part and it doesn't fit, you may still be able to return it, but some retailers charge a restocking fee.

Can I upgrade parts later?

Yes. You can add more RAM, swap the storage drive for a larger one, upgrade the graphics card, or replace the CPU and motherboard together. The case and power supply usually stay the same unless you're upgrading to much more powerful parts.

Do I need a graphics card if I'm not gaming?

No. Most modern CPUs have built-in graphics that handle web browsing, office work, and video watching fine. You only need a separate graphics card if you're gaming, doing 3D rendering, or running machine learning software.

What's the difference between DDR4 and DDR5 RAM?

DDR5 is newer and faster, but it's also more expensive. For gaming and everyday use, DDR4 is still plenty fast. Buy whichever type your motherboard supports — you can't mix them.