Before generation of Microprocessors i.e. in 1st, 2nd and 3rd generation computers, the 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 in the late 1970s. The Central Processing Unit, memory and peripherals were housed on individual printed circuit boards which plugged into the backplane. (A backplane is a circuit board that connects several connectors in parallel to 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.)
During the late 1980s and 1990s, it was found that increasing the number of peripheral functions on the PCB was very economical. Hence, single Integrated Circuits (ICs), capable of supporting low-speed peripherals like serial ports, mouse, keyboards, etc., were included on the motherboards. By the late 1990s, motherboards began to have full range of audio, video, storage and networking functions on them. Higher end systems for 3D gaming and graphic cards were also included later.
Micronics, Mylex, AMI, DTK, Orchid Technology, Elitegroup, etc. were few companies that were early pioneers in the field of motherboard manufacturing but, companies like Apple and IBM soon took over.
Today, motherboards typically boast a wide variety of built-in features, and they directly affect a computer’s capabilities and potential for upgrades.
Today Intel and Asus are the two leading companies in the field of motherboard manufacturing.
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. Few things that a motherboard nowadays include are:
• sockets (or slots) in which one or more microprocessors may be installed. • slots into which the system’s main memory is to be installed (typically in the form of DIMM modules containing DRAM chips). • a chipset which forms an interface between the CPU’s front-side bus, main memory, and peripheral buses. • non-volatile memory chips (usually Flash ROM in modern motherboards) containing the system’s firmware or BIOS. • a clock generator which produces the system clock signal to synchronize the various components. • slots for expansion cards (these interface to the system via the buses supported by the chipset).
• power connectors, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards. • Additionally, nearly all motherboards include logic and connectors to support commonly used input devices, such as PS/2 connectors for a mouse and keyboard. Occasionally video interface hardware is also integrated into the motherboard. Additional peripherals such as disk controllers and serial ports are provided as expansion cards. • Given the high thermal design power of high-speed computer CPUs and components, modern motherboards nearly always include heat sinks and mounting points for fans to dissipate excess heat. [pic]
• A CPU socket or slot is an electrical component that attaches to a printed circuit board (PCB) and is designed to house a CPU (also called a microprocessor). • It is a special type of integrated circuit socket designed for very high pin counts. A CPU socket provides many functions, including a physical structure to support the CPU, support for a heat sink, facilitating replacement (as well as reducing cost), and most importantly, forming an electrical interface both with the CPU and the PCB. • CPU sockets can most often be found in most desktop and server computers (laptops typically use surface mount CPUs), particularly those based on the Intel x86 architecture on the motherboard. A CPU socket type and motherboard chipset must support the CPU series and speed.
• It is possible to include support for many peripherals on the motherboard. By combining many functions on one PCB, the physical size and total cost of the system may be reduced; highly integrated motherboards are thus especially popular in small form factor and budget computers.
Peripheral Card Slots
• A standard ATX motherboard will typically have one PCI-E 16x connection for a graphics card, two conventional PCI slots for various expansion cards, and one PCI-E 1x. A standard EATX motherboard will have one PCI-E 16x connection for a graphics card, and a varying number of PCI and PCI-E 1x slots. It can sometimes also have a PCI-E 4x slot. • Some motherboards have two PCI-E 16x slots, to allow more than 2 monitors without special hardware, or use a special graphics technology called SLI (for Nvidia) and Crossfire (for ATI). These allow 2 graphics cards to be linked together, to allow better performance in intensive graphical computing tasks, such as gaming and video editing.
• Virtually all motherboards come with at least four USB ports on the rear, with at least 2 connections on the board internally for wiring additional front ports that may be built into the computer’s case. • Ethernet is also included. Ethernet is a standard networking cable for connecting the computer to a network or a modem. • A sound chip is always included on the motherboard, to allow sound output without the need for any extra components. This allows computers to be far more multimedia-based than before. Some motherboards contain video outputs on the back panel for integrated graphics solutions.
• Motherboards are generally air cooled with heat sinks often mounted on larger chips, such as the Northbridge, in modern motherboards. If the motherboard is not cooled properly, it can cause the computer to crash. • Passive cooling, or a single fan mounted on the power supply, was sufficient for many desktop computer CPUs until the late 1990s; since then, most have required CPU fans mounted on their heat sinks, due to rising clock speeds and power consumption. Most motherboards have connectors for additional case fans as well. • Newer motherboards have integrated temperature sensors to detect motherboard and CPU temperatures, and controllable fan connectors which the BIOS or operating system can use to regulate fan speed. Some computers use a water-cooling system instead of many fans.
Bus & Bus Speed
• A bus is simply a circuit that connects one part of the motherboard to another. The more data a bus can handle at one time, the faster it allows information to travel. The speed of the bus, measured in megahertz (MHz), refers to how much data can move across the bus simultaneously. • Bus speed usually refers to the speed of the front side bus (FSB), which connects the CPU to the northbridge. FSB speeds can range from 66 MHz to over 800 MHz. Since the CPU reaches the memory controller though the northbridge, FSB speed can dramatically affect a computer’s performance. [pic]
• The speed of the chipset and busses controls how quickly it can communicate with other parts of the computer. The speed of the RAM connection directly controls how fast the computer can access instructions and data, and therefore has a big effect on system performance. A fast processor with slow RAM is going nowhere. • The amount of memory available also controls how much data the computer can have readily available. RAM makes up the bulk of a computer’s memory. The general rule of thumb is the more RAM the computer has, the better. • Much of the memory available today is dual data rate (DDR) memory. This means that the memory can transmit data twice per cycle instead of once, which makes the memory faster. Also, most motherboards have space for multiple memory chips, and on newer motherboards, they often connect to the northbridge via a dual bus instead of a single bus. This further reduces the amount of time it takes for the processor to get information from the memory. • A motherboard’s memory slots directly affect what kind and how much memory is supported. Just like other components, the memory plugs into the slot via a series of pins. The memory module must have the right number of pins to fit into the slot on the motherboard.
• Motherboards are produced in a variety of sizes and shapes called computer form factor, some of which are specific to individual computer manufacturers. • The current desktop PC form factor of choice is ATX. A case’s motherboard and PSU form factor must all match, though some smaller form factor motherboards of the same family will fit larger cases. For example, an ATX case will usually accommodate a microATX motherboard. • Laptop computers generally use highly integrated, miniaturized and customized motherboards. This is one of the reasons that laptop computers are difficult to upgrade and expensive to repair. Often the failure of one laptop component requires the replacement of the entire motherboard, which is usually more expensive than a desktop motherboard due to the large number of integrated components.
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