BIOS (basic input output system)
The BIOS is a mini operating system that resides on the motherboard and controls the interaction between the components. Advanced BIOSs will let you manipulate system settings, such as memory timings, CPU voltages and setting alerts if a fan fails or the temperature of a component reaches a critical level. This is particularly useful for those inclined towards overclocking.
Chipset
The chipset is the combination of specialised microprocessors on the motherboard that link all the components in the PC together. Traditionally, the chipset is made up of two major components: the Northbridge, which connects the CPU to the memory, and the Southbridge, which adds I/O connectivity. Other features can then be added through dedicated chips, such as VGA, Serial ATA, audio or networking. This architecture allows motherboard manufacturers to mix and match CPU types with different I/O configurations. Some common chipsets are the Intel 875 series, VIA KT600 and NVIDIA nForce2.
CMOS (complementary metal oxide semiconductor)
CMOS is a type of semiconductor, but commonly refers to the memory where the BIOS settings are stored. If your BIOS settings get corrupted or incorrectly set, you can usually set a jumper on the motherboard to reset the CMOS to load the default BIOS settings.
FSB (front side bus)
The FSB is the rate at which the CPU communicates with the main system memory. It is usually denoted in terms of frequency, although this can be deceptive, as most FSBs are double or quad 'pumped', such as with the Pentium 4. In this case, a Pentium 4 with an 800MHz FSB is actually running at 200MHz, but is quad pumped. As such, four times the bandwidth can be gleaned from a lower frequency.
HyperTransport
HyperTransport is a point-to-point, 16-bit, high frequency bus, meaning it doesn't require a third chip, like a Northbridge, to link two components. Currently it is used by AMD for its AMD64 chips, the Athlon 64 and Opteron. The Athlon 64 uses one HyperTransport bus to connect to the rest of the system, while the Opteron features three HyperTransport busses per processor, which allows multiple processors to be 'glued' together without needing special chipset support.
Motherboard
The motherboard, also called the mainboard, is the backbone of the modern PC. It is the platform onto which all other components are connected, including the CPU, memory and peripherals. Motherboard manufacturers will usually use a chipset from one of the several main chipset vendors, then tweak the layout and add other functionality through third-party chips. This means two motherboards from different manufacturers with the same chipset will have very similar features, but there will be small differences in the BIOS features and additional functionality, like integrated networking or audio.
Northbridge
The Northbridge is one of the main components of the motherboard chipset. It is a specialised processor that manages the connectivity between the CPU (or CPUs), the memory, the AGP or PCI Express busses and the Southbridge. The features of the Northbridge determine the type of CPU supported by the motherboard, as well as the front side bus speed and memory type and speed. Some Northbridges, such as the Intel 865G, also include integrated graphics which shares the main memory with the CPU.
PCI (peripheral control interconnect)
PCI is an older I/O interconnect for peripherals like network, sound and other I/O cards. Desktop PCI is typically a 32-bit bus that runs at 33MHz, for a total bandwidth of 133MB/s. This bandwidth is shared with all other peripherals, though, and is inadequate for future high-bandwidth devices, such as Gigabit Ethernet, which alone can use up to 125MB/s. As such, it is in the process of being replaced by PCI Express.
PCI Express
PCI Express, originally called 3GIO, is the replacement technology for PCI. It is a serial bus, with each channel capable of handling 2.5Gb/s, or around 300MB/s. Multiple channels can also be bound together, such as with PCI Express 16X, which is expected to replace AGP for bandwidth-intensive graphics cards.
PGA (pin grid array)
PGA is a type of connector for CPUs, and usually resembles a square socket with hundreds of holes that fit the pins on the underside of the CPU. In nomenclature terms, the number after the 'PGA' denotes the number of pins on the CPU. Other connectors also exist, such as slots, where the CPU is mounted on a daughter board which then connects to the motherboard, or BGA (ball grid array), which is mainly used on notebooks. A new connector, LGA (land grid array) is about to be introduced with the new Pentium 4s.
Southbridge
The Southbridge is the other main component of the motherboard chipset, and adds I/O (input/output) connectivity. This usually includes IDE, for hard disks and CD/DVD drives; PCI, for add in cards; and USB, FireWire and Serial and Parallel ports. Many motherboards also have additional chips for additional functionality, like Ethernet or audio, that connect to the Southbridge. PCI Express will eventually remove PCI from the Southbridge, and replace it with a dedicated 'switch' chip that enables each PCI Express peripheral to communicate directly with the Northbridge.