Modern motherboards include, at a minimum:
1.  sockets (or slots) in which one or more microprocessors may be installed
2.  slots into which the system’s main memory is to be installed
3.  a chipset which forms an interface between the CPU‘s front-side bus, main memory, and peripheral buses
4.  non-volatile memory chips containing the system’s firmware or BIOS
5.  a clock generator which produces the system clock signal to synchronize the various components
6.  slots for expansion cards (these interface to the system via the buses supported by the chipset)
7.  power connectors, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards

In personal computers, a motherboard is the central printed circuit board (PCB) in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple computers, the logic board. It is also sometimes casually shortened to mobo

Prior to the advent of the microprocessor, a computer was usually built in a card-cage case or mainframe with components connected by a backplane consisting of a set of slots themselves connected with wires; in very old designs the wires were discrete connections between card connector pins, but printed circuit boards soon became the standard practice.

A backplane (or “backplane system”) is a group of connectors connected in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a complete computer system. Backplanes commonly use a printed circuit board

While a motherboard may include a backplane for the addition of feature cards, a backplane can stand alone as a separate entity. A backplane is generally differentiated from a motherboard by the lack of on-board processing and storage elements.

Because of limitations inherent in the PCI specification for driving slots, backplanes are now offered as passive and active though the general usage is referred to as passive even when active components are present in the bus.

True passive backplanes offer no active bus driving circuitry. Any desired arbitration logic is placed on the daughter cards. Active backplanes include chips which buffer the various signals to the slots.

When a backplane is used with a plug-in single board computer (SBC) or system host board (SHB), the combination provides the same functionallity as a motherboard providing processing power, memory, I/O and slots for plug-in cards.

A motherboard, like a backplane, provides the electrical connections by which the other components of the system communicate, but unlike a backplane, it also connects the central processing unit and hosts other subsystems and devices.

A typical desktop computer has its microprocessor, main memory, and other essential components connected to the motherboard. Other components such as external storage, controllers for video display and sound, and peripheral devices may be attached to the motherboard as plug-in cards or via cables, although in modern computers it is increasingly common to integrate some of these peripherals into the motherboard itself.

A CPU socket or slot is an electrical component that attaches to a printed circuit board (PCB) and is designed to house a CPU.  A CPU socket provides many functions, including a physical structure to support the CPU, support for a heat sink, facilitating replacement, and most importantly, forming an electrical interface both with the CPU and the PCB.

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