What goes inside a working computer

A functioning PC needs seven essential parts: a motherboard, a CPU (processor), RAM (memory), a storage drive, a power supply, a case, and a cooling system. Everything else — graphics cards, extra fans, wireless cards — plugs into or sits alongside these core pieces. You cannot build a PC that turns on without all seven.

The motherboard is the backbone. It is a flat circuit board that holds the CPU, RAM, and storage drive, and it connects them so they can talk to each other. The CPU is the brain that does the actual thinking. RAM is the short-term memory the CPU uses while working. The storage drive holds your files and operating system when the computer is off. The power supply converts wall electricity into the right voltage for each part. The case is the box that holds everything and protects it. The cooling system — usually fans and heatsinks — keeps the CPU from overheating.

Key Takeaways

  • You must have a motherboard, CPU, RAM, storage drive, power supply, case, and cooling system for any PC to work at all.
  • The motherboard socket type determines which CPUs fit, so you choose the CPU before you buy the motherboard, or vice versa.
  • RAM and storage are separate — RAM is fast temporary memory, and storage is permanent space for files and the operating system.
  • The power supply wattage must be higher than your parts draw, and the case must physically fit your motherboard size and cooling height.
  • Most CPUs come with a basic cooler, but some do not, so check before you buy.

The motherboard: where everything connects

The motherboard is a large circuit board with slots and connectors for every other part. It comes in three main sizes: ATX (full-size, about 12 by 10 inches), Micro-ATX (smaller, about 9 by 9 inches), and Mini-ITX (smallest, about 6.7 by 6.7 inches). The size you choose affects which case you need and how many expansion slots you have room for.

The motherboard also has a socket — a specific slot where the CPU sits. Intel and AMD CPUs use different sockets, and each generation of CPUs uses different sockets too. An Intel LGA1700 socket will not fit an AMD Ryzen CPU, and an older Intel socket will not fit a newer Intel CPU. You must match the motherboard socket to the CPU you plan to buy. If you are starting from scratch, pick the CPU first, then buy a motherboard with the matching socket.

The motherboard also determines how much RAM you can install (usually 2 to 4 slots), what kind of storage drives connect to it (SATA or NVMe), and whether you have room for a graphics card. Check the motherboard manual or product page to see how many RAM slots it has and what the maximum capacity is.

The CPU: the processor that does the work

The CPU (central processing unit) is a small chip that sits in the motherboard socket under a metal cooler. It is the part that actually runs programs and games. CPUs come from two main makers: Intel and AMD. Within each brand, there are different generations and models, each with its own socket type and power draw.

When you shop for a CPU, you will see a model number like "Intel Core i5-13600K" or "AMD Ryzen 5 5600X". The number and letter tell you roughly how powerful it is and what generation it is. A newer generation is usually faster than an older one, even if the model number looks similar. The socket type is what matters most for compatibility — it must match your motherboard socket exactly.

Most CPUs come with a cooler in the box, but some do not. Intel's K-series chips (like the i5-13600K) and AMD's X-series chips (like the Ryzen 5 5600X) often ship without a cooler. Check the product page before you buy so you know whether you need to buy a cooler separately.

RAM and storage: memory and space are not the same thing

RAM (random access memory) is fast, temporary memory that the CPU uses while running programs. It clears when you shut down the computer. Storage is permanent space where your files, photos, and operating system live. They are completely different, and you need both.

RAM comes in sticks that slot into vertical connectors on the motherboard. Most modern PCs use DDR4 or DDR5 RAM. The motherboard manual tells you which type it accepts — you cannot mix them. Most people buy 16 GB of RAM for general use (two 8 GB sticks), though 32 GB is becoming standard for video editing or 3D work. The motherboard has a maximum capacity, usually listed in the manual or on the product page.

Storage comes in two types: SSD (solid state drive) and HDD (hard disk drive). SSDs are much faster and are what you want for your operating system and main programs. HDDs are slower but cheaper per gigabyte, so some people use them for backup or file storage. Most new builds use at least one SSD. NVMe SSDs plug directly into the motherboard and are faster than SATA SSDs. SATA drives use a cable connection. Check your motherboard to see how many M.2 slots (for NVMe) and SATA ports it has.

The power supply: wattage and efficiency matter

The power supply converts electricity from your wall outlet into the right voltage and current for each part. It has cables that plug into the motherboard, CPU, graphics card (if you have one), and storage drives. You need a power supply with enough wattage to handle all your parts under load, plus some headroom.

To find the right wattage, add up the power draw of your CPU and GPU (if you have one). A typical CPU draws 65 to 125 watts, and a graphics card draws 150 to 450 watts depending on the model. Add those together and multiply by 1.3 to give yourself headroom. If your CPU draws 105 watts and your GPU draws 320 watts, you need at least (105 + 320) × 1.3 = 552 watts. A 650-watt power supply would be safe.

Power supplies also have an efficiency rating: 80 Plus Bronze, Silver, Gold, or Platinum. A higher rating means less wasted heat and lower electricity bills over time. Gold is a good middle ground. Avoid the cheapest no-name supplies — a failing power supply can damage your other parts.

The case: size and airflow

The case is the metal box that holds everything. It must fit your motherboard size (ATX, Micro-ATX, or Mini-ITX) and have enough vertical space for your CPU cooler. Cases come in full-size, mid-tower, and mini-tower shapes. A full-size ATX case fits an ATX motherboard. A mid-tower usually fits Micro-ATX or smaller. A mini-tower is tight and limits your options.

Check the case specifications for the maximum CPU cooler height it supports. If your cooler is 160 mm tall and the case supports only 150 mm, it will not fit. The case should also have at least two fans (one intake, one exhaust) or room to add them. Good airflow keeps your parts cool and extends their life.

The cooling system: keeping the CPU from overheating

The CPU generates heat and must be cooled or it will shut down or damage itself. Most CPUs come with a basic cooler in the box — usually a metal heatsink with a fan attached. This cooler is adequate for normal use and light gaming.

If you buy a CPU without a cooler, or if you want better cooling for heavy gaming or video editing, you can buy an aftermarket cooler. Air coolers are simpler and cheaper (usually $30 to $80). Liquid coolers are more expensive ($80 to $200+) but cool better and look flashier. Both types work fine. The cooler must fit your motherboard socket and fit inside your case.

The cooler attaches to the CPU with thermal paste (a thin layer of conductive goo that helps heat transfer). Most coolers come with thermal paste already applied, so you do not need to buy it separately.

Optional parts that enhance but are not required

Once you have the seven core parts, you can add extras. A graphics card (GPU) lets you play demanding games or do 3D work. Many CPUs have built-in graphics that work for everyday tasks and light gaming, so a separate GPU is optional. A wireless card or WiFi module lets you connect to the internet without an ethernet cable — some motherboards have this built in. Extra case fans improve airflow. RGB lighting and cable extensions are purely cosmetic.

Do not buy these until you have the core seven parts working. Start with the basics, test the build, and add extras later if you want them.

Frequently Asked Questions

Can I use a CPU cooler from an old computer?

Only if the socket type matches. An old Intel cooler will not fit a new AMD motherboard, and an old socket type will not fit a new one. Check the cooler's compatibility list or the motherboard manual before reusing one.

What if I buy the wrong RAM type for my motherboard?

It will not fit into the slot. DDR4 and DDR5 RAM have different notches and are not interchangeable. Check your motherboard manual for the exact RAM type before you buy.

Do I need a graphics card if my CPU has built-in graphics?

No, not for everyday use. Built-in graphics handle web browsing, video, and office work fine. You only need a separate graphics card for demanding games, 3D rendering, or video editing.

What happens if my power supply is too weak?

The computer may not turn on, or it may shut down randomly under load. In rare cases, an undersized power supply can fail and damage other parts. It is better to buy a supply with more wattage than you think you need.

Can I put an ATX motherboard in a Mini-ITX case?

No. An ATX motherboard is too large. You must match the motherboard size to the case size. A Mini-ITX motherboard fits in a Mini-ITX case, and also fits in larger cases, but not the other way around.