Exam 5: The System Unit

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Expansion buses are the channels that allow for additional hardware or peripherals to be connected to the computer's motherboard. These buses enable the computer to be expanded beyond its original capabilities. There are several types of expansion buses, but the three principal types are:

1. **PCI (Peripheral Component Interconnect)**: Introduced in the early 1990s, PCI was a significant improvement over its predecessors. It is a hardware bus designed for attaching hardware devices in a computer. These devices can include network cards, modems, sound cards, and graphics cards. PCI supports bus mastering, which allows devices connected to the bus to communicate with each other without going through the CPU. This reduces the load on the processor and allows for better system performance. PCI has largely been replaced by PCI Express in modern systems.

2. **AGP (Accelerated Graphics Port)**: Specifically designed for the high demands of 3D graphics, AGP was introduced in 1997. It was used exclusively for graphics cards, providing a direct connection between the card and the memory. This direct connection allowed for higher bandwidth and more rapid data transfer, which resulted in better performance in 3D graphics applications. AGP has multiple standards like AGP 1x, 2x, 4x, and 8x, with each providing a faster data transfer rate. However, AGP has been largely phased out in favor of PCI Express.

3. **PCI Express (PCIe)**: The most recent and the most used expansion bus in modern computers, PCI Express, was introduced in the early 2000s. It uses a serial interface, unlike the parallel interface used by its predecessors. This allows for faster data transfer rates and greater flexibility. PCIe slots come in different sizes, such as x1, x4, x8, x16, and x32, which refers to the number of lanes that are available for data transfer. Each lane consists of two pairs of wires, one for sending and one for receiving data. This technology is used for a wide range of purposes, including graphics cards, solid-state drives, network cards, and more.

These expansion buses have evolved over time to accommodate the increasing demands for data transfer speed and bandwidth. While PCI and AGP have played significant roles in the development of computer expansion technology, PCI Express is currently the standard for new systems due to its versatility and high performance.