One of the great strengths of the PC architecture is that it is extensible, allowing a great variety of components to be added, thereby permitting the PC to perform functions its designers may never have envisioned. However, most PCs include a more-or-less standard set of components, including the following:

Motherboard

The motherboard, is the heart of a PC. It serves as "Command Central" to coordinate the activities of the system. Its type largely determines system capabilities. Motherboards include the following components:

Chipset

The chipset provides the intelligence of the motherboard, and determines which processors, memory, and other components the motherboard can use. Most chipsets are divided physically and logically into two components. The Northbridge controls cache and main memory and manages the host bus and PCI expansion bus. The Southbridge manages the ISA bus, bridges the PCI and ISA busses, and incorporates a Super I/O controller, which provides serial and parallel ports, the IDE interface, and other I/O functions. Some recent chipsets, notably models from Intel, no longer use the old Northbridge/Southbridge terminology, although the functionality and division of tasks is similar. Other recent chipsets put all functions on one physical chip.

CPU slot(s) and/or socket(s)

The type of CPU slot or socket determines which processors the motherboard can use. The most popular CPU connectors are Socket 370 (late-model Intel Pentium III and Celeron processors), Socket A (AMD Athlon and Duron), Socket 478 (current Celeron and Pentium 4), Socket 423 (old-style Pentium 4), Slot 1 (old-style Pentium II/III and Celeron), Slot A (older-style Athlon), and the obsolete Socket 7 (Intel Pentium and AMD K6-* processors). Some motherboards have two or more CPU connectors, allowing them to support multiple processors. A few motherboards have both Slot 1 and Socket 370 connectors, allowing them to support either type of CPU (but not both at once).

Voltage Regulator Module (VRM)

VRMs supply clean, tightly regulated voltage to the CPU. Faster CPUs draw more current. Good VRMs are expensive, so some motherboard makers use the lowest-rated VRM suitable for the fastest CPU the motherboard is designed to support. Better VRMs allow a motherboard to accept faster future CPUs with only a BIOS upgrade.

Memory slots

The type and number of memory slots (along with chipset limitations) determine the type and amount of memory you can install in a PC. Recent motherboards use 168-pin SDRAM DIMMs, 168- or 184-pin Rambus RIMMs, 184-pin DDR-SDRAM DIMMs, or some combination. Motherboards that use 30- or 72-pin SIMMs are obsolete.

Expansion bus slots

The type and number of expansion bus slots determine the type and number of expansion cards you can add to the system. Recent motherboards may have both PCI and ISA expansion slots, although many recent models have only PCI slots.

Integrated functions

Modern motherboards often include embedded functions, such as video and sound (and, less commonly, LAN and SCSI interfaces), that were formerly provided by add-on expansion cards. Embedded components reduce costs, and are better integrated and more reliable. Against those advantages, it may be difficult or impossible to upgrade embedded components, and you pay for those embedded components whether you use them or not. Integrated motherboards are often ideally suited for casual use, but most people will avoid them for high-performance systems and build à la carte from discrete components.

Processor

The processor or CPU is the engine that drives the PC. The CPU you use determines how fast the system runs and what operating systems and other software can run on it. Most PCs use processors from Intel (Pentium II/III/4 or Celeron) or AMD (Athlon or Duron). Processors vary in speed (currently 700 MHz to 3+ GHz), cost ($25 to $500+), physical connector (Socket 423, Socket 478, Socket 370, Socket A, Slot 1, Slot 2, Slot A, Socket 7, and so on), efficiency at performing various functions, and other respects. Although processors get much attention, the truth is that performance differences between a $50 processor and a $250 processor are relatively minor, typically a factor of two.

Memory

A PC uses Random Access Memory (RAM), also called simply memory, to store the programs and data with which it is currently working. RAM is available in many different types, speeds, and physical packages. The amount and type of RAM a system can use depends on its chipset, the type and number of RAM slots available, and other factors. The optimum amount of RAM depends on the operating system you run, how many and which programs you run simultaneously, and other considerations. Typical new PCs may have from 64 megabytes (MB)—marginally adequate for some environments—to 256 MB, which is sufficient for many people. Very few commercial desktop systems come standard with 512 MB or more, which is the amount now used by most "power users." Adding RAM is often a cost-effective upgrade for older systems, many of which have woefully inadequate RAM to run modern operating systems and programs.

Floppy disk drive

The humble floppy disk drive (FDD) was formerly used for everything from booting the PC to storing data to running programs to making backups, but has now been largely relegated to such infrequent uses as making emergency boot diskettes, loading updated device drivers, running diagnostics programs, or "sneakernetting" documents to other systems. Many people don't use their FDDs from one month to the next. The FDD has been officially declared a "legacy" device, and many PCs manufactured after mid-2000 do not have one. All of that said, the FDD remains important to millions of PC users because it is the only read/write removable storage device present on most current PCs.

Optical drive

CD-ROM drives began to appear on mainstream PCs in the early 1990s, became ubiquitous, and have remained generally unchanged except for improvements in speed and reliability. CD-ROM discs store 600+ MB of data in read-only form, and because they are capacious and cheap to produce, are commonly used to distribute software and data. CD-ROM drives can also play CD-DA (audio) discs and multimedia discs, which makes them popular for listening to music and playing games.

Hard disk drive

The hard disk drive (HDD) is the primary storage device on any PC. Unlike RAM, which retains data only while power remains applied, data written to an HDD remains stored there until you delete it. HDD space was formerly a scarce resource that users went to great lengths to conserve. Modern HDDs are so capacious (up to 200+ GB) and so inexpensive ($1.50/GB or less) that most people now regard disk space as essentially free. On the downside, modern HDDs can be difficult to install and configure, particularly in older systems, and their huge capacity makes some form of tape backup almost mandatory.

Video adapter

A video adapter, also called a graphics adapter, accepts video data from the computer and converts it into a form the monitor can display. In addition to image quality, the video adapter you use determines the sharpness, number of colors, and stability of the image your monitor displays. Most recent video adapters display text and simple graphics adequately, but video adapters vary greatly in their suitability for use with graphics-intensive software, including games.

Display

The display you use ultimately determines the quality of the video you see. Most PCs use traditional CRT monitors, but flat-panel LCD displays are an increasingly popular choice. Displays are available in a wide variety of sizes, capabilities, features, and prices, and choosing the right one is not a trivial task.

Sound adapter and speakers

All PCs can produce basic warning sounds and audible prompts using their built-in speakers, but for listening to audio CDs, playing games, watching DVDs with full surround sound, using the Internet to make free long-distance telephone calls, using voice-recognition software, and performing other PC audio functions, you'll need a sound card (or embedded motherboard sound adapter) and speakers or headphones.

Keyboard and mouse

PCs use several types of devices to accept user input—keyboards for entering text; mice, trackballs, and other pointing devices for working in the Windows graphical environment; and game controllers for playing modern graphical computer games and simulations.

Communications ports and devices

Communications ports allow a PC to connect to external peripherals such as printers, modems, and similar devices: serial ports, which are obsolescent but still important for some uses, parallel ports, which are still commonly used to connect printers, Universal Serial Bus (USB) ports, which are replacing legacy serial and parallel ports, and will eventually be the only general-purpose external communications ports used on PCs.

Case and power supply

The case (or chassis) is the outer shell that contains the PC and all internal peripheral devices. The power supply provides regulated power to all system components and cooling airflow to keep components from overheating.