Motherboard

Course Navigation

<< Previous - Data sizes and speeds				Next - Processor >>

Introduction to Motherboard

A motherboard is an electronic circuit board in a computer which interconnects hardware devices attached to it. Hardware it connects to include Central processing units, graphics cards, audio cards, storage drives. The motherboard facilitates communication between these devices, which allows the computer to operate. 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." 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

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

Serial

An outdated piece of technology, serial ports were most often used to connect the mouse.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. Serial ports can still be found in industrial/commercial applications including computer networking such as Cisco routers like the Cisco 800 Series.

An example of a serial port

PS/2

PS/2 ports (now outdated) were for connecting peripherals such as your keyboard and mouse to the computer. PS/2 based mice and keyboards have now been replaced by USB ports as the popular standard.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

Parallel

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 favor of USB. Since 2019, parallel ports started to be phased out of motherboards in favor of technologies such as USB.

SCSI

Pronounced "scuzzy" and stands for "small computer system interface". This was used primarily as a connection interface for tape drives and hard disk drives. SCSI has been superseded in favor of newer and cheaper technologies such as USB and Firewire.

USB

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

USB Speeds:

• USB 4.0 | USB 40 - 40 Gigabits per second
• USB 3.1 | SuperSpeed - 10 Gigabits per second (Gbps)
• USB 3.0 | SuperSpeed - 5 Gbps
• USB 2.0 | Hi-Speed - 480 Megabits per second (Mbps)
• USB 1.1 | Full-Speed - 12 Mbps
• USB 1.0 | Low-Speed - 1.5 Mbps

USB is one of the most successful interconnecting protocols in computing history. It can operate at up to 40 Gbps, 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 current generation of USB (4), known as "USB40", is capable of transferring data at speeds around 80 times faster than hi-speed USB (a whopping 40 Gbps)

USB version 1.1 supported two speeds, a full speed mode of 12 Mbps and a low speed mode of 1.5 Mbps. The 1.5Mbps mode is slower and less susceptible to Electromagnetic Interference (EMI). EMI is unwanted noise or interference in an electrical path or circuit caused by an outside source. Source Article, 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 480 Mbps. The 480 Mbps is known as High-Speed mode and was a tack on to compete with the Firewire Serial Bus.

The Universal Serial Bus is host controlled. There can only be one host per Bus. A computer bus is a link between components or devices connected to a computer. For example, a bus carries data between a CPU and the system memory via the motherboard. Source Article. The specification in itself, does not support any form of multi-master 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 to negotiate for the role of host. This is aimed at and limited to single point to point connection such as a mobile phone and personal organizer 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, similar to that of 10BaseT ethernetAn Ethernet standard that transmits at 10 Mbps over twisted wire pairs (telephone wire). Source Article. 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 chainingConnected in series, one after the other. Source Article 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 InterfaceA register-level interface that enables a host controller for USB or IEEE 1394 hardware to communicate with a host controller driver in software. Source Article Specifications: the Universal Host Controller Interface (UHCI) - developed by Intel, puts more of the burden on software (Microsoft), allowing for cheaper hardware; and the Open Host Controller Interface (OHCI) - developed by Compaq, Microsoft, and National Semiconductor, places more of the burden on hardware (Intel) and makes for simpler software.

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.

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 synchronize the host and receiver clocks.

USB supports plug and play 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 unplug the cable, 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 ForumThe USB Implementers Forum (USB-IF) is a nonprofit organization created to promote and support USB (Universal Serial Bus). Source Article at a cost. 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 organizations provide is an extra VID for non-commercial activities such as teaching, research or fiddling (The Hobbyist). The USB Implementor's 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

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. For most purposes, this interface was superseded by Thunderbolt.

Thunderbolt

Thunderbolt is a connectivity specification that was developed by Apple and Intel which is currently at version 4. It supports display out at speeds of up to 40 Gbps. It also supports Ethernet networking protocols, and also can be used for external storage. It can even be used to connect external graphics cards. It also supports the USB4 specification. Most Apple branded computers use Thunderbolt ports.

Slots

Slots are an opening in a computer where a peripheral 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 flavors, which will be described below. An alternative explanation for expansion slots can be found here.

Graphics Card

Graphics Card

Graphic cards, also called video cards or video adapters, convert signals into video signals so the images can be displayed on the monitor. While many low-end graphics units are built into the CPU 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 frame-rates in computer games.

Graphics cards are designed to offload rendering from the CPU. Some graphics cards can be powered by the motherboard and usually require a PCI-e slot. Higher-end cards require more power and thus will need a double 6-pin/8-pin connector that runs directly to the power supply. Standalone Graphics cards also include onboard memory for efficient rendering. Typical sizes of modern graphics cards include 4-16 GB of memory. Today, 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

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 components for multimedia applications such as: games, video/audio editing software, and music composition. Before, computers used to have sound capabilities built into the motherboard, while other computers required additional expansion cards. Now, the main method of sound used for computers is through either a USB speaker, or audio out through HDMI or DP.

Sound Card on Wikipedia.

Network Interface Cards (NICs)

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, while others required expansion NICs, either through M.2 or PCIe ports.

NICs on Wikipedia

PC Card

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. This technology has been largely superseded in favor of newer technologies such as ExpressCard.

PC Card on Wikipedia

Course Navigation

<< Previous - Data sizes and speeds				Next - Processor >>