Case A computer case encloses most of the components of a desktop computer system. It provides mechanical support and protection for internal elements such as the motherboard, disk drives, and power supply, and controls and directs the flow of cooling air over internal components. The case is also part of the system to control electromagnetic interference radiated by the computer and protects internal parts from electrostatic discharge. Large
tower cases provide space for multiple disk drives or other peripherals and usually stand on the floor, while desktop cases provide less expansion room. All-in-one style designs include a video display built into the same case. Portable and laptop computers require cases that provide impact protection for the unit. Hobbyists may decorate the cases with colored lights, paint, or other features, in an activity called
case modding.
Power supply Most personal computer power supply units meet the
ATX standard and convert from
alternating current (AC) at between 120 and 277
volts provided from a
power outlet to
direct current (DC) at a much lower voltage: typically 12, 5, or 3.3 volts.
Motherboard The motherboard is the main component of a computer. It is a board with
integrated circuitry that connects the other parts of the computer including the
CPU, the
RAM, the disk drives (
CD,
DVD,
hard disk, or any others) as well as any peripherals connected via the ports or the
expansion slots. The
integrated circuit (IC) chips in a computer typically contain billions of tiny
metal–oxide–semiconductor field-effect transistors (MOSFETs). Components directly attached to or to part of the motherboard include: • At least one
CPU (central processing unit), which performs the majority of computational tasks required for a computer to operate. Often described informally as the
brain of the computer, the CPU fetches program instructions from
random-access memory (RAM), decodes and executes them, then returns results for further processing by other components. This process is known as the
instruction cycle. Modern CPUs are
microprocessors fabricated on a
metal–oxide–semiconductor (MOS)
integrated circuit (IC) using advanced
semiconductor device fabrication techniques, often employing
photolithography. They are typically cooled using a
heatsink and
fan or a
liquid-cooling system. Many contemporary CPUs integrate an on-die
graphics processing unit (
GPU), eliminating the need for a discrete GPU in basic systems. CPU performance is influenced by clock speed—measured in gigahertz (GHz)—with common consumer processors ranging from 1 GHz to 5 GHz. Additionally, there is a growing trend toward
multi-core designs, where multiple processing cores are included on a single chip, enabling greater
parallelism and improved multitasking performance. • The internal bus connects the CPU to main memory via multiple communication lines—typically 50 to 100—divided into address, data, and control buses, each handling specific types of signals. Historically, parallel buses were dominant, but in the twenty-first century, high-speed serial buses (often using
serializer/deserializer (SerDes) technology) have largely replaced them, enabling greater data throughput over fewer physical connections. Examples include
PCI Express and
USB. In systems with multiple processors, an interconnect bus is used, traditionally coordinated by a
northbridge chip, which links the CPU, memory, and high-speed peripherals such as
PCI. The
southbridge handles communication with slower I/O devices such as storage and USB ports. However, in modern architectures like
Intel QuickPath Interconnect or
AMD Ryzen-based systems, these functions are increasingly integrated into the CPU itself, forming a
system on a chip (SoC)-like design. •
Random-access memory (RAM) stores code and data actively used by the CPU, organized in a
memory hierarchy optimized for access speed and predicted reuse. At the top of this hierarchy are
registers, located within the CPU core, offering the fastest access but extremely limited capacity. Below registers are multiple levels of
cache memory—L1, L2, and sometimes L3—typically implemented using
static random-access memory (SRAM). Caches have greater capacity than registers but less than main memory, and while slower than registers, they are significantly faster than
dynamic random-access memory (DRAM), which is used for main RAM. Caching improves performance by
prefetching frequently used data, thereby reducing
memory latency. When data is not found in the cache (a
cache miss), it is retrieved from main memory. RAM is volatile, meaning its contents are lost when the system loses power. In modern systems, DRAM is often of the
DDR SDRAM type, such as DDR4 or DDR5. • Permanent storage or non-volatile memory is typically higher capacity and cheaper than memory, but takes much longer to access. Historically, such storage was typically provided in the form of a hard drive, but
solid-state drives (SSD) are becoming cheaper and are much faster, thus leading to their increasing adoption. USB drives and network or cloud storage are also options. •
Read-only memory (ROM) contains firmware such as the
BIOS (Basic Input/Output System), which initializes hardware during the boot process—known as
booting or
bootstrapping—when the computer is powered on. This firmware is stored in a non-volatile memory chip, traditionally ROM or
flash memory, allowing updates in modern systems via
firmware update. • The BIOS manages essential functions, including boot sequence and power management through the
ACPI standard. However, most modern motherboards have transitioned to the
Unified Extensible Firmware Interface (UEFI), which offers enhanced capabilities, faster startup times, support for
GUID Partition Table (GPT), and secure boot features. • The
CMOS (complementary MOS)
battery, which powers the
CMOS memory for date and time in the BIOS chip. This battery is generally a
watch battery. •
Power MOSFETs make up the
voltage regulator module (VRM), which controls how much
voltage other hardware components receive.
Expansion cards An
expansion card in computing is a printed circuit board that can be inserted into an expansion slot of a computer motherboard or backplane to add functionality to a computer system via the expansion bus. Expansion cards can be used to obtain or expand on features not offered by the motherboard. Using expansion cards for a video processor used to be common, but modern computers are more likely to instead have a GPU integrated into the motherboard.
Input/output Most computers also have an external data bus to connect peripheral devices to the motherboard. Most commonly,
Universal Serial Bus (USB) is used. Unlike the internal bus, the external bus is connected using a bus controller that allows the peripheral system to operate at a different speed from the CPU.
Input and
output devices are used to receive data from the external world or write data, respectively. Common examples include keyboards and
mice (input) and displays and printers (output).
Network interface controllers are used to access
the Internet. USB ports also allow power to connected devices—a standard USB supplies power at 5 volts and up to 500
milliamps (2.5
watts), while powered USB ports with additional pins may allow the delivery of more power—up to 6
amps at 24v. ==Sales==