Motherboard

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Introduction to Motherboard[edit]

A motherboard is an electronic circuit board in a computer which interconnects hardware devices attached to it. At a minimum it includes one or more Central processing units, and the main processing activity of the computer takes place on it. However, other connected printed circuit boards may contain their own microprocessors, either to take some of the load off of the motherboard or to perform specialized tasks better than the general-purpose hardware on the motherboard could. These boards, together with other plug-in boards without CPUs, may be called "daughter boards." It was called a "mother" board in relation to these. A PC motherboard may have a series of sockets, allowing daughter boards to be plugged in directly. Other connectors on the motherboard allow communication through cables with various peripheral devices, both inside and outside the computer case.

Ports[edit]

Ports are used by a motherboard to interface with electronics both inside and outside of the computer.

Serial[edit]

An outdated piece of technology, serial ports were most often used to connect the mouse. By circa 2000, most personal computers stopped relying on serial ports and were replaced by PS/2 and/or USB ports.

A serial Port
An example of a serial port

PS/2[edit]

PS/2 ports (now outdated) were for connecting peripherals such as your keyboard and mouse to the computer. PS/2 based mice and keyboards have now been replaced by USB ports as the popular standard. This trend for USB over PS/2 started in circa 2004.

Parallel[edit]

Parallel ports are used to connect other peripherals such as joysticks, and more commonly, printers. Similar to the serial port, this technology is slowly being phased out in favour of USB. Parallel ports can still be found in many motherboards today.

SCSI[edit]

Pronounced "scuzzy", this was used primarily as a connection interface for tape drives and hard disk drives. SCSI has been superseded in favour of newer and cheaper technologies such as USB and Firewire.

USB[edit]

Universal Serial Bus (USB*) is a connectivity specification, currently at version 3, and known as "hi-speed USB".

USB is one of the most successful interconnect in computing history. It operates at 480 Mbps and can be found in over 2 billion PC, CE, and mobile devices. USB has strong consumer brand recognition and a reputation for ease-of-use. The next generation of USB, known as "super-speed USB", is capable of transferring data as speeds 10 times that of hi-speed USB (Thats a whopping 4.8 Gb/s!).

USB version 1.1 supported two speeds, a full speed mode of 12Mbits/s and a low speed mode of 1.5Mbits/s. The 1.5Mbits/s mode is slower and less susceptible to EMI, thus reducing the cost of ferrite beads and quality components. For example, crystals can be replaced by cheaper resonators. USB 2.0 which is still yet to see day light on mainstream desktop computers has upped the stakes to 480Mbits/s. The 480Mbits/s is known as High Speed mode and was a tack on to compete with the Firewire Serial Bus.

USB Speeds High Speed - 480Mbits/s Full Speed - 12Mbits/s Low Speed - 1.5Mbits/s The Universal Serial Bus is host controlled. There can only be one host per bus. The specification in itself, does not support any form of multimaster arrangement. However the On-The-Go specification which is a tack on standard to USB 2.0 has introduced a Host Negotiation Protocol which allows two devices negotiate for the role of host. This is aimed at and limited to single point to point connections such as a mobile phone and personal organiser and not multiple hub, multiple device desktop configurations. The USB host is responsible for undertaking all transactions and scheduling bandwidth. Data can be sent by various transaction methods using a token-based protocol.

In my view the bus topology of USB is somewhat limiting. One of the original intentions of USB was to reduce the amount of cabling at the back of your PC. Apple people will say the idea came from the Apple Desktop Bus, where both the keyboard, mouse and some other peripherals could be connected together (daisy chained) using the one cable.

However USB uses a tiered star topology, simular to that of 10BaseT Ethernet. This imposes the use of a hub somewhere, which adds to greater expense, more boxes on your desktop and more cables. However it is not as bad as it may seem. Many devices have USB hubs integrated into them. For example, your keyboard may contain a hub which is connected to your computer. Your mouse and other devices such as your digital camera can be plugged easily into the back of your keyboard. Monitors are just another peripheral on a long list which commonly have in-built hubs.

This tiered star topology, rather than simply daisy chaining devices together has some benefits. Firstly power to each device can be monitored and even switched off if an overcurrent condition occurs without disrupting other USB devices. Both high, full and low speed devices can be supported, with the hub filtering out high speed and full speed transactions so lower speed devices do not receive them.

Up to 127 devices can be connected to any one USB bus at any one given time. Need more devices? - simply add another port/host. While most earlier USB hosts had two ports, most manufacturers have seen this as limiting and are starting to introduce 4 and 5 port host cards with an internal port for hard disks etc. The early hosts had one USB controller and thus both ports shared the same available USB bandwidth. As bandwidth requirements grew, we are starting to see multi-port cards with two or more controllers allowing individual channels.

The USB host controllers have their own specifications. With USB 1.1, there were two Host Controller Interface Specifications, UHCI (Universal Host Controller Interface) developed by Intel which puts more of the burden on software (Microsoft) and allowing for cheaper hardware and the OHCI (Open Host Controller Interface) developed by Compaq, Microsoft and National Semiconductor which places more of the burden on hardware(Intel) and makes for simpler software. Typical hardware / software engineer relationship. . .

With the introduction of USB 2.0 a new Host Controller Interface Specification was needed to describe the register level details specific to USB 2.0. The EHCI (Enhanced Host Controller Interface) was born. Significant Contributors include Intel, Compaq, NEC, Lucent and Microsoft so it would hopefully seem they have pooled together to provide us one interface standard and thus only one new driver to implement in our operating systems. Its about time.

USB as its name would suggest is a serial bus. It uses 4 shielded wires of which two are power (+5v & GND). The remaining two are twisted pair differential data signals. It uses a NRZI (Non Return to Zero Invert) encoding scheme to send data with a sync field to synchronise the host and receiver clocks.

USB supports plug’n’plug with dynamically loadable and unloadable drivers. The user simply plugs the device into the bus. The host will detect this addition, interrogate the newly inserted device and load the appropriate driver all in the time it takes the hourglass to blink on your screen provided a driver is installed for your device. The end user needs not worry about terminations, terms such as IRQs and port addresses, or rebooting the computer. Once the user is finished, they can simply lug the cable out, the host will detect its absence and automatically unload the driver.

The loading of the appropriate driver is done using a PID/VID (Product ID/Vendor ID) combination. The VID is supplied by the USB Implementor's forum at a cost and this is seen as another sticking point for USB. The latest info on fees can be found on the USB Implementor’s Website

Other standards organisations provide a extra VID for non-commercial activities such as teaching, research or fiddling (The Hobbyist). The USB Implementors forum has yet to provide this service. In these cases you may wish to use one assigned to your development system's manufacturer. For example most chip manufacturers will have a VID/PID combination you can use for your chips which is known not to exist as a commercial device. Other chip manufacturers can even sell you a PID to use with their VID for your commercial device.

Another more notable feature of USB, is its transfer modes. USB supports Control, Interrupt, Bulk and Isochronous transfers. While we will look at the other transfer modes later, Isochronous allows a device to reserve a defined amount of bandwidth with guaranteed latency. This is ideal in Audio or Video applications where congestion may cause loss of data or frames to drop. Each transfer mode provides the designer trade-offs in areas such as error detection and recovery, guaranteed latency and bandwidth.

Firewire[edit]

Technically known as the IEEE 1394 interface, but dubbed by Apple as Firewire, this connection medium hoped to surpass USB in terms of speed and popularity. While it did outperform USB v2 in speed tests, uptake was very limited due to the existing widespread use of USB.

Slots[edit]

Slots are an opening in a computer where a circuit board can be inserted to add new capabilities. All personal computers contain expansion slots for adding more memory, graphics capabilities, and support for special devices. Expansion slots come in different flavours, which will be described below. An alternative explanation for expansion slots can be found here.

Graphics card[edit]

Graphics Card

Graphic cards- are also called video card's or a video adapter. They are in all PCs. Graphic cards convert signals into video signals so the images can be displayed on the monitor. While many graphics cards are built into the motherboard these days, enthusiasts will invest in standalone graphics cards with stronger and more powerful processing capabilities. This allows for heavy image editing, or better rendering and framerates in computer games.

Graphics cards are designed to offload rendering from the CPU. Graphics cards are powered by the motherboard and require a PCIX or PCIX 2.0 slot to install. Some cards require more power and thus will need a 6-8 pin connector that runs directly to the power supply. Graphics cards also include on board memory for efficient rendering. Typical sizes include 128-1024mb of memory. Today, high end graphics cards have multiple core processors that are largely parallel to increase texture fill and process more 3D objects in real time.

Graphics Card on Wikipedia

Sound card[edit]

Close-up of a Sound Card

A sound card, also referred to as an audio card facilitates the input and output of audio signals to and from a computer under the control of computer programs. Sound cards for computers were uncommon until 1988, which left the single internal PC speaker as the only way early PC software could produce sound and music.

Uses of a sound card include the audio component's for multimedia applications such as games, video/audio editing software and music composition. Most computers today have sound capabilities built into the motherboard, while others require additional expansion cards.

Sound Card on Wikipedia.

Network Interface Cards (NICs)[edit]

Network Interface Card

Network Interface Cards can be a network card, network adapter, LAN Adapter or NIC (network interface card). They are a piece of computer hardware designed to allow computers to communicate over a computer network. Used for remote communication via cable. Data is transmitted over a cable network. The NIC connects computers and other devices such as printers. Many modern motherboards have NICs built in by default.

NICs on Wikipedia

PC Card[edit]

A PC Card (originally PCMCIA Card; short for Personal Computer Memory Card International Association) is a device that uses a specific peripheral interface designed for laptop computers.

PC Card on Wikipedia