What Is a PC?

To see how a PC works, let's start with the pieces that come together to make up the machine, aka as the computer hardware. The following are the components common to PCs in the order they're typically assembled:

Case: If you're using a laptop, the computer case includes keyboard and screen. For desktop PCs, the case is typically some type of box with lights, vents, and places for attaching cables. The size of the case can vary from small tabletop units to tall towers. A larger case doesn't always imply a more powerful computer; it's what's inside that counts. PC builders design or select a case based on the type of motherboard that should fit inside.

Motherboard: The primary circuit board inside your PC is its motherboard. All components, inside and out, connect through the motherboard in some way. The other components listed on this page are removable and, thus, replaceable without replacing the motherboard. Several important components, though, are attached directly to the motherboard. These include the complementary metal-oxide semiconductor (CMOS), which stores some information, such as the system clock, when the computer is powered down. Motherboards come in different sizes and standards, the most common as of this writing being ATX and MicroATX. From there, motherboards vary by the type of removable components they're designed to handle internally and what ports are available for attaching external devices. For power users, there is also the E-ATX form factor, which has more space for ports and expansion slots, but requires a large PC case to accommodate it.

Power supply: Other than its CMOS (complementary metal-oxide semiconductor or microchip), which is powered by a replaceable CMOS battery on the motherboard, every component in your PC relies on its power supply. The power supply connects to some type of power source, whether that's a battery in the case of mobile computers, or a power outlet in the case of desktop PCs. In a desktop PC, you can see the power supply mounted inside the case with a power cable connection on the outside and a handful of attached cables inside. Some of these cables connect directly to the motherboard while others connect to other components like drives and fans.

Central processing unit (CPU): The CPU, often just called the processor, is the component that contains the microprocessor. That microprocessor is the heart of all the PC's operations, and the performance of both hardware and software rely on the processor's performance. Intel and AMD are the largest CPU manufacturers for PCs, though you'll find others on the market, too. The two common CPU architectures are 32-bit and 64-bit, and you'll find that certain software relies on this architecture distinction. Modern CPU designs typically contain four or more cores to allow them to complete multiple tasks at once, efficiently.

Random-access memory (RAM): Even the fastest processor needs a buffer to store information while it's being processed. The RAM is to the CPU as a countertop is to a cook: It serves as the place where the ingredients and tools you're working with wait until you need to pick up and use them. Both a fast CPU and an ample amount of RAM are necessary for a speedy PC. Each PC has a maximum amount of RAM it can handle, and slots on the motherboard indicate the type of RAM the PC requires. DDR-4 is the type of RAM chipDD supported by most motherboards today, but some systems are upgrading to the newer and faster DDR-5 standard as well.

Drives: A drive is a device intended to store data when it's not in use. A hard drive or solid state drive stores a PC's operating system and software, which we'll look at more closely later. In many systems, there is also room for additional drives to be installed for expanded storage. This category also includes optical drives such as those used for reading and writing CD, DVD and Blu-ray media. A drive connects to the motherboard based on the type of drive controller technology it uses, including the older IDE standard and the newer SATA standard. Current laptops and mini computers are likely to use compact NVME SSDs that connect via M.2 connector pins mounted directly to the motherboard.

Cooling devices: The more your computer processes, the more heat it generates. The CPU and other components can handle a certain amount of heat. However, if a PC isn't cooled properly, it can overheat, causing costly damage to its components and circuitry. Fans are the most common device used to cool a PC. In addition, the CPU is covered by a metallic block called a heat sink, which draws heat away from the CPU. Some serious computer users, such as gamers, sometimes have more expensive heat management solutions, like a water-cooled system, designed to deal with more intense cooling demands.

Cables: All the components we've mentioned so far are connected by some combination of cables. These cables are designed to carry data, power or both. PCs should be constructed so that the cables fold neatly within the case and do not block air flow throughout it.

A PC is typically much more than these core components. Next, we'll look at the ports and peripherals that let you interact with the computer and how you can add even more components using expansion slots.

The core components we've looked at so far make up a PC's central processing power. A PC needs additional components, though, for interacting with human users and other computers. The following are the PC parts that make this happen:

Graphics components: While some motherboards have on-board graphics, others include what's called an expansion slot, where you can slide in a separate video card, also known as a GPU (graphics processing unit). In both cases, the video components in a PC process some of the complex graphics data going to the screen, taking some of the load off your CPU. A motherboard accepts video cards based on a specific interface, such as the older AGP standard or one of the newer PCI standards. Modern video cards can take up a large amount of space inside the PC case because they need dedicated video RAM and additional cooling fans in order to deliver high performance.

Ports: The word port is often used to describe a place on the outside of your PC where you can plug in a cable. Describe a port by its use, such as a USB port or an ethernet port. (Note that the word port is also used to describe a software connection when two pieces of hardware try to communicate.) Many ports are affixed directly to the motherboard. Some of the ports you'll find on a PC include the following:

Peripherals: Any piece of hardware that isn't mounted inside a PC's case is called a peripheral. This includes your basic input and output devices: monitors, keyboards and mice. It also includes printers, speakers, headphones, microphones, webcams and USB flash drives. Anything you can plug in to a port on the PC is one of the PC's peripherals. The essential peripherals (such as monitors) aren't necessary on laptops, which have them built in instead.

Expansion slots: On occasion, you'll want to add components to a PC that don't have a designated slot somewhere on the motherboard. That's why the motherboard will include a series of expansion slots. The removable components designed to fit into expansion slots are called cards, probably because of their flat, card-like structure. Using expansion slots, you can add extra video cards, network cards, printer ports, TV receivers and many other custom additions. The card must match the expansion slot type, whether it's the legacy ISA/EISA type, the more common PCI, PCI-X or PCI Express types, or the newer M.2 standard.

Now that we've looked at the parts of a PC, let's press the power button and see what makes it boot.

When you first power up a PC, the machine goes through several internal processes before it's ready for you to use. This is called the boot process or booting the PC. Boot is short for bootstrap, a reference to the old adage, "Pull yourself up by the bootstraps," which means to start something from the very beginning. The boot process is controlled by the PC's basic input-output system (BIOS).

The BIOS is software stored on a flash memory chip. In a PC, the BIOS is embedded on the motherboard. Occasionally, a PC manufacturer will release an update for the BIOS, and you can carefully follow instructions to "flash the BIOS" with the updated software.

Besides controlling the boot process, the BIOS provides a basic configuration interface for the PC's hardware components. In that interface, you can configure such things as the order to read drives during boot and how fast the processor should be allowed to run. Check your PC's documentation to find out how to enter its BIOS interface. This information is often displayed when you first boot the computer, too, with a message such as, "Press DEL to enter Setup Menu."

The following is a summary of the boot process in a PC:

Now that we're all powered up, what's next? A great deal of how PCs work depends on the operating system you use. In the next section, let's examine how operating systems work on a PC.

After a PC boots, you can control it through an operating system, or OS for short. As of this writing, most non-Apple PCs run a version of Microsoft Windows or a Linux distribution. These operating systems are designed to run on various kinds of PC hardware, while Mac OS X is designed primarily for Apple hardware.

An operating system is responsible for several tasks. These tasks fall into the following broad categories:

Now let's look at the future of PCs overall and the way that PC manufacturers have conquered the portability challenges of mobile computing.

Since the first PC hit the market, newer and better models have made older models obsolete within months of production. Drive technologies like SATA replaced IDE, and PCI expansion slots replaced ISA and EISA. The most prominent gauge for technological progress in a PC, though, is its CPU and the microprocessor within that CPU.

Silicon microprocessors have been the heart of the computing world since the 1950s. During that time, microprocessor manufacturers have crammed more transistors and enhancements onto microprocessors. In 1965, Intel founder Gordon Moore predicted that microprocessors would double in complexity every two years. Since then, that complexity has doubled every 18 months, and industry experts dubbed the prediction Moore's Law. Many experts have predicted that Moore's Law will reach an end soon because of the physical limitations of silicon microprocessors [source: PBS].

As of this writing, though, processors' transistor capacities continue to rise. This is because chip manufacturers are constantly finding new ways to etch transistors onto the silicon. The tiny transistors are now measured in nanometers, which is one billionth of a meter. Atoms themselves are approximately 0.5 nm. The smaller transistors get, the more can be fit onto one CPU, increasing the relative processing power. In 2023, Intel launched its 13th generation Raptor Lake CPU architecture, which uses transistors with 10 nanometers of thickness. Additionally, IBM has created prototype chips with two-nanometer transistors. That's only four atoms across, but consumer applications are at least a few years down the road.

So what happens when we reach the end of Moore's Law? A new means of processing data could ensure that progress continues. Potential successors are those that prove to be a more powerful means of performing the basic computational functions of a processor. Silicon microprocessors have relied on the traditional two-state transistor for more than 50 years, but inventions such as quantum computers are changing the game.

Quantum computers aren't limited to the two states of 1 or 0. They encode information as quantum bits, or qubits. A qubit can be a 1 or a 0, or it can exist in a superposition that is simultaneously 1 and 0 or somewhere in between. Qubits represent atoms that are working together to serve as both computer memory and microprocessor. Because a quantum computer can contain these multiple states simultaneously, it has the potential to be millions of times more powerful than today's most powerful supercomputers.

Current quantum computers look like giant golden towers, resembling an intricate piece of jewelry more than any PC in your home. The technology is still young, and mostly exists only in lab settings. However, IBM is currently maintaining quantum machines that universities and research firms can access via cloud interface to do things like solve complex equations or run physics simulations.

Time will tell whether the power of quantum computers will ever make it to the average PC. In the meantime, you can still carry a lot of processing power with you thanks to mobile PCs, which we'll look at next.

Even before the PC, computer manufacturers were conceptualizing portable computers. It was the 12-pound (5-kilogram) IBM PC Convertible that brought the laptop concept into production in 1986. Since then, laptop computers have become smaller and lighter, and their processing power has improved alongside desktop PCs.

Today, the computer industry recognizes other classes of mobile computers. One class, the notebook computer, has become almost synonymous with the laptop. The term was originally used to indicate a smaller, lighter cousin to the laptop. Another class, the netbook, is even smaller than notebooks, while also being cheaper and less powerful. The classification is probably named for its target audience: those who want a very basic interface for using the Internet.

Mobile computing goes even further than notebooks and netbooks. Many smartphones and tablets have as much processing power as notebooks, packed into smaller packages. The key differences include a smaller screen size and resolution, fewer external ports, cellular phone capability and touch-screen technology, in addition to or in place of a keyboard. Due to limited space, phones are also usually saddled with lower amounts of RAM.

On the software side, PC operating systems are also improving portability. For example, Google Chrome OS minimizes the need for hard drive space by relying on access to web applications and cloud storage. This means a netbook that's limited to a 64 GB solid-state drive has the potential to be as useful as a laptop with a 500 GB disk drive. Naturally, large applications that aren't web-enabled are the exception to this space-saving advantage.