Hardware (computer)

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Hardware Connections

To function, hardware requires physical connections that allow components to communicate and interact. A bus provides a common interconnected system composed of a group of wires or circuitry that coordinates and moves information between the internal parts of a computer. A computer bus consists of two channels, one that the CPU uses to locate data, called the address bus, and another to send the data to that address, called the data bus. A bus is characterized by two features: how much information it can manipulate at one time, called the bus width, and how quickly it can transfer these data. In today’s computers, a series of buses work together to communicate between the various internal and external devices.

A

Internal Connections

Expansion, or add-on, cards use one of three bus types to interface with the computer. The Peripheral Connection Interface (PCI) is the standard expansion card bus used in most computers. The Accelerated Graphics Port (AGP) bus was developed to create a high-speed interface with the CPU that bypassed the PCI bus. This bus was specifically designed for modern video cards, which require a large amount of bandwidth to communicate with the CPU. A newer version of PCI called PCI Express (PCIe) was designed to replace both PCI and AGP as the main bus for expansion cards.

Internal storage devices use one of three separate standards to connect to the bus: parallel AT attachment (PATA), serial AT attachment (SATA), or small computer system interface (SCSI). The term AT refers to the IBM AT computer, first released in 1984. The PATA and SCSI standards were first introduced in 1986; the SATA standard was introduced in 2002 as a replacement for the PATA standard. The SCSI standard is mainly used in servers or high-end systems.

A

1

Parallel and Serial Connections

For most of the history of the personal computer, external and internal devices have communicated to each other through parallel connections. However, given the limitations of parallel connections, engineers began to develop technology based on serial connections, since these have greater data transfer rates, as well as more reliability.

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A serial connection is a wire or set of wires used to transfer information from the CPU to an external device such as a mouse, keyboard, modem, scanner, and some types of printers. This type of connection transfers only one piece of data at a time. The advantage to using a serial connection is that it provides effective connections over long distances.

A parallel connection uses multiple sets of wires to transfer blocks of information simultaneously. Most scanners and printers use this type of connection. A parallel connection is much faster than a serial connection, but it is limited to shorter distances between the CPU and the external device than serial connections.

The best way to see the difference between parallel and serial connections is to imagine the differences between a freeway and a high-speed train line. The freeway is the parallel connection—lots of lanes for cars. However, as more cars are put onto the freeway, the slower each individual car travels, which means more lanes have to be built at a high cost if the cars are to travel at high speed. The train line is the serial connection; it consists of two tracks and can only take two trains at a time. However, these trains do not need to deal with traffic and can go at higher speeds than the cars on the freeway.

As CPU speeds increased and engineers increased the speed of the parallel connections to keep up, the main problem of parallel connections—maintaining data integrity at high speed—became more evident. Engineers began to look at serial connections as a possible solution to the problem. This led to the development of both SATA and PCI Express, which, by using serial connections, provide high data transfer rates with less materials used and no data loss.

B

External Connections

The oldest external connections used by computers were the serial and parallel ports. These were included on the original IBM PC from 1981. Originally designed as an interface to connect computer to computer, the serial port was eventually used with various devices, including modems, mice, keyboards, scanners, and some types of printers. Parallel ports were mainly used with printers, but some scanners and external drives used the parallel port.

The Universal Serial Bus (USB) interface was developed to replace both the serial and parallel ports as the standard for connecting external devices. Developed by a group of companies including Microsoft, Intel, and IBM, the USB standard was first introduced in 1995. Besides transferring data to and from the computer, USB can also provide a small amount of power, eliminating the need for external power cables for most peripherals. The USB 2.0 standard, which came into general usage in 2002, drastically improved the data transfer rate.

A competing standard to USB was developed at the same time by Apple and Texas Instruments. Officially called IEEE 1394, it is more commonly called FireWire. It is capable of transferring data at a higher rate than the original USB standard and became the standard interface for multimedia hardware, such as video cameras. But Apple’s royalty rate and the introduction of USB 2.0—as well as the fact that Intel, one of the companies behind USB, is responsible for most motherboards and chipsets in use—meant that FireWire was unlikely to become the standard peripheral interface for PCs. Today most computers have both USB and FireWire ports connected to the motherboard.

Wireless devices have also become commonplace with computers. The initial wireless interface used was infrared (IR), the same technology used in remote controls. However, this interface required that the device have a direct line of sight to the IR sensor so that the data could be transferred. It also had a high power requirement. Most modern wireless devices use radio frequency (RF) signals to communicate to the computer. One of the most common wireless standards used today is Bluetooth. It uses the same frequencies as the Wi-Fi standard used for wireless LANs.

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