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How PCs Work

Most of us use a computer every single day, but few people know about the inner workings of this vital part of our lives.

The word computer refers to an object that can accept some input and produce some output. In fact, the human brain itself is a sophisticated computer, and scientists are learning more about how it works with each passing year. Our most common use of the word computer, though, is to describe an electronic device containing a microprocessor.

A microprocessor is a small electronic device that can carry out complex calculations in the blink of an eye. You can find microprocessors in many devices you use each day, such as cars, refrigerators and televisions. The most recognized device with a microprocessor is the personal computer, or PC. In fact, the concept of a computer has become nearly synonymous with the term PC.

When you hear PC, you probably envision an enclosed device with an attached video screen, keyboard and some type of a pointing device, like a mouse or touchpad. You might also envision different forms of PCs, such as desktop computers, towers and laptops. The term PC has been associated with certain brands, such as Intel processors or Microsoft operating systems. In this article, though, we define a PC as a more general computing device with these characteristics:

  • designed for use by one person at a time
  • runs an operating system to interface between the user and the microprocessor
  • has certain common internal components described in this article, like a CPU and RAM
  • runs software applications designed for specific work or play activities
  • allows for adding and removing hardware or software as needed

PCs trace their history back to the 1970s when a man named Ed Roberts began to sell computer kits based on a microprocessor chip designed by Intel. Roberts called his computer the Altair 8800 and sold the unassembled kits for $395. Popular Electronics ran a story about the kit in its January 1975 issue, and to the surprise of just about everyone, the kits became an instant hit. Thus, the era of the personal computer began [sources: Cerruzi, Lasar].

While the Altair 8800 was the first real personal computer, it was the release of the Apple II a couple of years later that signaled the start of the PC as a sought-after home appliance. The Apple II, from inventors Steve Jobs and Steve Wozniak, proved that there was a demand for computers in homes and schools. Soon after, long-established computer companies like IBM and Texas Instruments jumped into the PC market, and new brands like Commodore and Atari jumped into the game.

In this article, we'll look inside the PC to find out about its parts and what they do. We'll also check out the basic software used to boot and run a PC. Then, we'll cover mobile PCs and examine the future for PC technology.

Core PC Components

To see how a PC works, let's start with the pieces that come together to make up the machine. 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.

Power supply -- Other than its CMOS, 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.

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.

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. 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.

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.

Ports, Peripherals and Expansion Slots

Ideally, your computer will have enough ports that you won't have to jumble all your accessories together. If you find yourself in a jam like this, consider whether or not you need all those peripherals.
Ideally, your computer will have enough ports that you won't have to jumble all your accessories together. If you find yourself in a jam like this, consider whether or not you need all those peripherals.
© balcazar

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. 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.

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:

  • USB ports
  • network ports, typically Ethernet and FireWire
  • video ports, typically some combination of VGA, DVI, RCA/component, S-Video and HDMI
  • audio ports, typically some combination mini analog audio jacks or RCA
  • legacy ports, or ports that follow old standards which are rarely used in modern computers, such as parallel printer ports and PS2 ports for a keyboard and mouse

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 or the more common PCI, PCI-X or PCI Express types.

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

Powering Up a PC

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:

  1. The power button activates the power supply in the PC, sending power to the motherboard and other components.
  2. The PC performs a power-on self-test (POST). The POST is a small computer program within the BIOS that checks for hardware failures. A single beep after the POST signals that everything's okay. Other beep sequences signal a hardware failure, and PC repair specialists compare these sequences with a chart to determine which component has failed.
  3. The PC displays information on the attached monitor showing details about the boot process. These include the BIOS manufacturer and revision, processor specs, the amount of RAM installed, and the drives detected. Many PCs have replaced displaying this information with a splash screen showing the manufacturer's logo. You can turn off the splash screen in the BIOS settings if you'd rather see the text.
  4. The BIOS attempts to access the first sector of the drive designated as the boot disk. The first sector is the first kilobytes of the disk in sequence, if the drive is read sequentially starting with the first available storage address. The boot disk is typically the same hard disk or solid-state drive that contains your operating system. You can change the boot disk by configuring the BIOS or interrupting the boot process with a key sequence (often indicated on the boot screens).
  5. The BIOS confirms there's a bootstrap loader, or boot loader, in that first sector of the boot disk, and it loads that boot loader into memory (RAM). The boot loader is a small program designed to find and launch the PC's operating system.
  6. Once the boot loader is in memory, the BIOS hands over its work to the boot loader, which in turn begins loading the operating system into memory.
  7. When the boot loader finishes its task, it turns control of the PC over to the operating system. Then, the OS is ready for user interaction.

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.

PC Operating Systems

Microsoft Windows continues to be the most popular operating system in the world.
Microsoft Windows continues to be the most popular operating system in the world.
© Kujansuu

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:

  • Processor management -- breaks down the processor's work into manageable chunks and prioritizes them before sending them to the CPU.
  • Memory management -- coordinates the flow of data in and out of RAM, and determines when to use virtual memory on the hard disk to supplement an insufficient amount of RAM.
  • Device management -- provides a software-based interface between the computer's internal components and each device connected to the computer. Examples include interpreting keyboard or mouse input or adjusting graphics data to the right screen resolution. Network interfaces, including managing your Internet connection, also fall into the device management bucket.
  • Storage management -- directs where data should be stored permanently on hard drives, solid state drives, USB drives and other forms of storage. For example, storage management tasks assist when creating, reading, editing, moving, copying and deleting documents.
  • Application interface -- provides data exchange between software programs and the PC. An application must be programmed to work with the application interface for the operating system you're using. Applications are often designed for specific versions of an OS, too. You'll see this in the application's requirements with phrases like "Windows Vista or later," or "only works on 64-bit operating systems."
  • User interface (UI) - provides a way for you to interact with the computer.

From there, make a note to see our article How Operating Systems Work for more details about how an OS functions on a PC. Also, check with HowStuffWorks when you want to know how specific applications and devices work on your PC.

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

The Future of PCs

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, and the most current production processes for microprocessors can produce transistors that measure 45 nm or 32 nm. The smaller that number goes, the more transistors will fit onto a chip and, thus, the more processing power the chip is capable of. As of May 2011, Intel was working on a 22-nm manufacturing process, code-named Ivy Bridge, which uses transistors with an energy-conserving design called Tri-Gate [sources: BBC, Intel].

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. Quantum computing technology is still in its early stages, but scientists are already proving the concept with real, measurable results. Be sure to check out How Quantum Computers Work for more on this amazing breakthrough.

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.

Portable Personal Computing

Mobile computing devices will continue to become more and more prominent in the PC market.
Mobile computing devices will continue to become more and more prominent in the PC market.
© Mark

Even before the PC, computer manufacturers were conceptualizing portable computers. It was the 12-pound 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 [source: IBM].

Today, the computer industry recognizes other classes of mobile computers. One class, the notebook, 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 that 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.

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.

In this article, we've looked at how a PC works and where PC technology is going. One thing is certain: the PC will evolve. It will get faster. It will have more capacity. And it will continue to be an integral part of our lives.

For lots more on personal computers, click on the next page.

Related Articles

More Great Links


  • BBC News. "Intel unveils 22nm 3D Ivy Bridge processor." BBC. May 4, 2011. (Nov. 1, 2011)
  • Ceruzzi, Paul E. "A History of Modern Computing, 2nd Edition." Massachusetts Institute of Technology. 2003.
  • Lenovo. "Company History." (Nov. 1, 2011)
  • Intel. "From Sand to Silicon: the Making of a Chip: 32nm Process Technology." Intel Corporation. (Nov. 1, 2011)
  • Lasar, Matthew. "Who invented the personal computer? (hint: not IBM)." Ars Technica. Condé Nast Digital. June 2011. (Oct. 31, 2011)
  • "The First Silicon Transistor." ScienCentral, Inc. and The American Institute of Physics. 1999. (Nov. 1, 2011)