Compression by the SIP

As telephone-based 56k modems began losing popularity, some Internet service providers such as Netzero and Juno started using pre-compression to increase the throughput and maintain their customer base. As example, the Netscape ISP uses a compression program that squeezes images, text, and other objects at the modem server, just prior to sending them across the phone line. Certain content using lossy compression (e.g., images) may be recompressed (transcoded) using different parameters to the compression algorithm, making the transmitted content smaller but of lower quality. The server-side compression operates much more efficiently than the on-the-fly compression of V.44-enabled modems due to the fact that V.44 is a generalized compression algorithm whereas other compression techniques are application-specific (JPEG, MPEG, Vorbis, etc.). Typically Website text is compacted to 4% thus increasing effective throughput to approximately 1,300 kbit/s. The accelerator also pre-compresses Flash executables and images to approximately 30% and 12%, respectively.

The drawback of this approach is a loss in quality, where the GIF and JPEG images are lossy compressed, which causes the content to become pixelated and smeared. However the speed is dramatically improved such that Web pages load in less than 5 seconds, and the user can manually choose to view the uncompressed images at any time. The ISPs employing this approach advertise it as "surf 5× faster" or simply "accelerated dial-up".

Voice Modem

Voice modems are regular modems that are capable of recording or playing audio over the telephone line. They are used for telephonyapplications. See Voice modem command set for more details on voice modems. This type of modem can be used as an FXO card forPrivate branch exchange systems (compare V.92).

Compression by the SIP

As telephone-based 56k modems began losing popularity, some Internet service providers such as Netzero and Juno started using pre-compression to increase the throughput and maintain their customer base. As example, the Netscape ISP uses a compression program that squeezes images, text, and other objects at the modem server, just prior to sending them across the phone line. Certain content using lossy compression (e.g., images) may be recompressed (transcoded) using different parameters to the compression algorithm, making the transmitted content smaller but of lower quality. The server-side compression operates much more efficiently than the on-the-fly compression of V.44-enabled modems due to the fact that V.44 is a generalized compression algorithm whereas other compression techniques are application-specific (JPEG, MPEG, Vorbis, etc.). Typically Website text is compacted to 4% thus increasing effective throughput to approximately 1,300 kbit/s. The accelerator also pre-compresses Flash executables and images to approximately 30% and 12%, respectively.

The drawback of this approach is a loss in quality, where the GIF and JPEG images are lossy compressed, which causes the content to become pixelated and smeared. However the speed is dramatically improved such that Web pages load in less than 5 seconds, and the user can manually choose to view the uncompressed images at any time. The ISPs employing this approach advertise it as "surf 5× faster" or simply "accelerated dial-up".

Using Digital Lines

In the late 1990s Rockwell and U.S. Robotics introduced new technology based upon the digital transmission used in modern telephony networks. The standard digital transmission in modern networks is 64 kbit/s but some networks use a part of the bandwidth for remote office signaling (e.g., to hang up the phone), limiting the effective rate to 56 kbit/sDS0. This new technology was adopted into ITU standards V.90 and is common in modern computers. The 56 kbit/s rate is only possible from the central office to the user site (downlink). In the United States, government regulation limits the maximum power output, resulting in a maximum data rate of 53.3 kbit/s. The uplink (from the user to the central office) still uses V.34 technology at 33.6 kbit/s.

Later in V.92, the digital PCM technique was applied to increase the upload speed to a maximum of 48 kbit/s, but at the expense of download rates. For example a 48 kbit/s upstream rate would reduce the downstream as low as 40 kbit/s, due to echo on the telephone line. To avoid this problem, V.92 modems offer the option to turn off the digital upstream and instead use a 33.6 kbit/s analog connection, in order to maintain a high digital downstream of 50 kbit/s or higher. V.92 also adds two other features. The first is the ability for users who have call waiting to put their dial-up Internet connection on hold for extended periods of time while they answer a call. The second feature is the ability to quickly connect to one's ISP. This is achieved by remembering the analog and digital characteristics of the telephone line, and using this saved information to reconnect at a fast pace.

Soft Modem

A Winmodem or softmodem is a stripped-down modem that replaces tasks traditionally handled inhardware with software. In this case the modem is a simple interface designed to create voltage variations on the telephone line and to sample the line voltage levels (digital to analog and analog to digital converters). Softmodems are cheaper than traditional modems, since they have fewer hardware components. One downside is that the software generating and interpreting the modem tones is not simple (as most of the protocols are complex), and the performance of the computer as a whole often suffers when it is being used. For online gaming this can be a real concern. Another problem is lack of portability such that non-Windows operating systems (such as Linux) often do not have an equivalent driver to operate the modem.

A modem (modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from driven diodes to radio.

The most familiar example is a voice band modem that turns the digital data of a personal computer into modulated electrical signals in thevoice frequency range of a telephone channel. These signals can be transmitted over telephone lines and demodulated by another modem at the receiver side to recover the digital data.

Modems are generally classified by the amount of data they can send in a given time unit, normally measured in bits per second (bit/s, or bps). They can also be classified by the symbol rate measured in baud, the number of times the modem changes its signal state per second. For example, the ITU V.21 standard used audio frequency-shift keying, aka tones, to carry 300 bit/s using 300 baud, whereas the original ITU V.22 standard allowed 1,200 bit/s with 600 baud using phase shift keying.

Form Factor

Motherboards are produced in a variety of sizes and shapes called computer form factor, some of which are specific to individual computer manufacturers. However, the motherboards used in IBM-compatible to fit variouscase sizes. As of 2007, most desktop computer motherboards use one of these standard form factors—even those found in Macintosh and Sun computers, which have not traditionally been built from commodity components. 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.

Peripheral Card Slots

A typical motherboard of 2009 will have a different number of connections depending on its standard.

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 (which will eventually supersede PCI). A standard EATXmotherboard 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. (This varies between brands and models.)

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.

As of 2007, 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. This 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 have their graphics chip built into the motherboard rather than needing a separate card. A separate card may still be used.

With the steadily declining costs and size of integrated circuits, it is now possible to include support for many peripherals on the motherboard. By combining many functions on onePCB, 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.

For example, the ECS RS485M-M, a typical modern budget motherboard for computers based on AMD processors, has on-board support for a very large range of peripherals:

• disk controllers for a floppy disk drive, up to 2 PATA drives, and up to 6 SATA drives (including RAID 0/1 support)
• integrated graphics controller supporting 2D and 3D graphics, with VGA and TV output
• integrated sound card supporting 8-channel (7.1) audio and S/PDIF output
• Fast Ethernet network controller for 10/100 Mbit networking
• USB 2.0 controller supporting up to 12 USB ports
• IrDA controller for infrared data communication (e.g. with an IrDA-enabled cellular phone or printer)
• temperature, voltage, and fan-speed sensors that allow software to monitor the health of computer components

Expansion cards to support all of these functions would have cost hundreds of dollars even a decade ago; however, as of April 2007 such highly integrated motherboards are available for as little as $30 in the USA.

Overview

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.

An important component of a motherboard is the microprocessor's supporting chipset, which provides the supporting interfaces between the CPU and the various buses and external components. This chipset determines, to an extent, the features and capabilities of the motherboard.

History

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. The Central Processing Unit, memory and peripherals were housed on individual printed circuit boards which plugged into the backplane.

During the late 1980s and 1990s, it became economical to move an increasing number of peripheral functions onto the motherboard (see below). In the late 1980s, motherboards began to include single ICs (called Super I/O chips) capable of supporting a set of low-speed peripherals: keyboard, mouse, floppy disk drive, serial ports, and parallel ports. As of the late 1990s, many personal computer motherboards supported a full range of audio, video, storage, and networking functions without the need for any expansion cards at all; higher-end systems for 3D gaming and computer graphics typically retained only the graphics card as a separate component.

The early pioneers of motherboard manufacturing were Micronics, Mylex, AMI, DTK, Hauppauge, Orchid Technology, Elitegroup, DFI, and a number of Taiwan-based manufacturers.

Motherboard

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, while providing connectors for other peripherals. The motherboard is sometimes alternatively known as the main board, system board, or, on Apple computers, the logic board. It is also sometimes casually shortened to mobo.