Remembering old friends - SCSI

In many ways, the SCSI interface is like an old friend. It's been around since 1982 in one form or another. SCSI - Small Components Software Interface - is more than just a parallel interface; it is also a protocol. The first version, SCSI-1 was introduced to the market in 1982 and offered what was then a convenient means of connecting peripheral devices.

SCSI-2 has been available since 1986. Depending on the bus bandwidth, anywhere from 7 to 15 devices can be connected to the SCSI bus. It offers two bandwidths, 8 and 16-bit, which deliver data transfer rates of 5 and 10 Mbytes per second respectively. Its primary purpose is to connect external peripherals like hard drives, scanners, MO drives and controllers.

UltraSCSI, the next generation of SCSI-2, doubles speeds to 20 MHz, which combined with a 16-bit wide bus (known as WIDE16) allows for transfer rates of 40 Mbytes per second. Obviously, SCSI has not been left behind in the battle for more data transfer performance. Looking to the future, SCSI will be able to connect even more things over longer distances.

One of the more exciting recent developments, Fibre Channel, uses the SCSI protocol but in connection with a serial interface. It offers serial data transfer rates up to 200 MB per second, 30-metre copper wire lengths and support for 126 devices. SSA, a technology developed by IBM for its own high-end peripherals, also uses the SCSI-2 protocol and provides data transfer rates up to 80 MB/s, 20-metre cable lengths and support for 126 devices. Although the performance of SCSI has improved over the years, it is facing fierce - if not fatal - competition from newer technologies, such as Fibre Channel and 1394.

SCSI inside notebooks, however, has not proved popular and is rarely seen. Because SCSI is used for stationary peripherals, it is usually included in docking stations.

It's all in the (PC) cards

Along with PCI bus technology, which is ultimately a key factor for easy expansion and flexibility, it is important to look at what is being connected to this bus.

PC Cards, formerly known as PCMCIA cards, are the quickest and easiest way of expanding a mobile computing environment. In the early 1990's, these small credit-card shaped adapters for PCs quickly became standard equipment in mobile computers. Like many technologies, PC Card technology has grown up in recent years. Many different types of these credit-card size devices are available - ranging from hard disk drives and modem cards to network cards and ISDN cards.

All of these PC Cards also bring a whole new meaning to the word connectivity. Think of the modem card that connects users to Internet providers. Or the Ethernet card that provides a LAN connection. In this area, a lot of exciting developments can be seen. Xircom has introduced a credit card Ethernet Adapter 10/100 that allows notebook users to connect to 10Mbps and 100Mbps Ethernet networks. For mobile PC users, connectivity is all in the cards.

CardBus, a recent development, is an extension of the latest PC Card standard. It is derived from the PCI architecture and is capable of 32-bit, 33 MHz operation. CardBus is beneficial for higher data throughput needed for high-bandwidth applications, such as high-speed networking.