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Input-Output (I/O) Technologies
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Computer Technology
This web page was written as a University project on the 2nd of June 1999, and its purpose is to shed light on some new I/O (input/output) devices, namely USB (Universal Serial Bus), IEEE 1394/1394b (FireWire/iLink) and SCSI (Ultra2 and Ultra160/m). This web site consists of an information page and two data sheet pages. The information in this web page was taken from many sources, a lot of the data present was 'learnt' from Personal Computer World magazine what inspired me to create a web site on this topic, and without which this web site would have been impossible.
Please have a browse around, some of the information is quite enlightening, if you have any information you think should be added to this web page or if you notice any mistakes or if you just have any questions you think I may be able to answer please do not hesitate to e-mail me on the following address: [email protected]
Read on... and, thanks for visiting my web page.
Site creator, Peter G. Liverpool, UK.
1) FireWire, USB and SCSI information page.
2) FireWire, USB and SCSI devices data sheet.
3) FireWire, USB and SCSI data sheet.
1) IEEE 1394, 1394b, USB,SCSI Buses.
With the recent increase in computer power and program size it has become necessary to develop new and faster Bus connector options. For years the PC has been graced with an array of different I/O (Input/Output) facilities, including Parallel, Serial, PS/2, IDE ports.
The throughput of these devices are relatively low, serial ports transfer data at 115.2Kbps, parallel ports transfer data at about 500Kbps (according to type), and IDE of which there is now two types, transfers data at ATA33 (33Mb/s) or ATA66 (66Mb/s) burst rates, or about 7-8Mb/s sustained transfer.
Modern devices and programs are becoming increasingly 'bandwidth hungry' requiring more memory and speed, also with the introduction of new memory devices such as DVD (Digital Versatile Disk) and new multimedia devices, it has become necessary to attach far more 'faster' devices to a computer, and now the legacy I/O ports are being stretched to their limits which is causing an I/O 'bottleneck'.
Recently there has been the introduction of a new I/O port, the USB (Universal Serial Bus) which has been standard on many motherboards for the last few years but until recently has had few supporting devices or OS (Operating System) compatibility. Now hundreds of USB devices are available, and with its advanced features such as plug and play, hot swap capability, and power through host bus, not mentioning its 1.5Mb/s transfer speed and ability to connect up to 127 devices, it is looking to replace most of the current legacy I/O ports (Serial, Parallel, PS/2).
Along with the introduction of USB, another faster more versatile port was introduced, IEEE 1394, Institute of Electrical and Electronic Engineers 1394 bus. This port was originally developed by Apple under the name of 'FireWire' (Sony call it i.Link). FireWire was developed as a DV (Digital Video) connector as its bandwidth was so high, but its potential as a general data transfer medium has been recognised and various high performance media will soon be available. FireWire has many advantages over other data transfer buses, first its ability to handle sustained data transfer rates of up to 50Mb/s (400Mbit/s), hot swappable, plug and play protocol, peer to peer operation and power through the IEEE 1394 cable. Another advantage of FireWire is its ability to support different speed devices on the same bus without slowing down the faster devices, in other words you can mix fast and slow devices on the same bus without reducing the top speed of the fastest device. There are two standard ports for IEEE 1394 a small and large port for various reasons, such as device size and aesthetics.
In the next few months we expect to see the release of IEEE 1394b which is strictly the same thing as IEEE 1394 but with a different system of data encoding. This different system of encoding increases the buses bandwidth to top out at 200Mb/s (1600Mbit/s), also with the introduction of bus-bridging technology, up to 64,000 1394/1394b devices can, in theory, be attached.
FireWire and USB when used in conjunction are complementary, they address all the limitations of legacy I/Os. USB deals with slower devices, and FireWire deals with the faster devices. Both support plug and play and hot swapping. Eventually all peripherals will be connected to a PC via USB and FireWire.
Furthermore IEEE 1394 (FireWire) has found its way into the consumer market and will soon be standard on most electronic equipment, such as TVs, Videos, DVDs, Sound systems, Satellite receivers, Digital cameras and video-cameras, GPS, giving true multimedia capability. USB will never make it on to the consumer market due to certain limitations, such as no peer to peer.
Eventually USB will 'die off' as it does not offer some of the advanced features of FireWire or the incredible bandwidth, and in a few years hundreds of devices will be available for FireWire, it will support all the devices currently supported for by USB plus a huge array of hardware and multimedia/consumer devices.
For years the standard way of attaching internal devices to a PC has been via two internal IDE channels, each channel capable of supporting two devices, therefore making it possible to attach a total of four internal devices. Whilst the PC had IDE, the Apple computers were supplied with a SCSI (Small Computer Systems Interface) as standard, SCSI is far superior to IDE as it is capable of supporting between four and fifteen devices, varying in transfer speeds from 8Mb/s to a whopping 160Mb/s, also SCSI is capable of attaching external drives and high performance scanners making it far more versatile than IDE. SCSI has been introduced into the PC via an add on ISA or PCI card or in some cases it is incorporated into the motherboard. The incorporation of a SCSI bus into a PC gives it the capability to have an increased number of devices attached that are running at an increased data transfer rate, this is essential for data intensive applications and devices, high speed workstations and particularly servers. SCSI has not really found its way into the household desktop computer mainly for the reason of implementation costs, also most desktops do not require the increased bandwidth provided by SCSI.
SCSI has been around for years, but recently there has been the introduction of Ultra2 and Ultra160/m SCSI which have peak transfer rates of 80Mb/s and 160Mb/s respectively this gives the modern SCSI bus the edge over other drive device attachment methods. The cost of a modern SCSI PCI card can be expensive and can only be justified in high throughput computers were this extra speed and device addition capability is necessary, also modern SCSI devices are far more expensive than IDE devices and once again this extra cost can only be justified where speed and large storage capacity is essential. SCSI provides a high speed, high capacity device addition system which is far superior to IDE and gives a computer increased versatility and future proofing.
With the addition of SCSI, USB and FireWire to a PC, makes it an exceedingly versatile device capable of handling large data throughput at high speeds, with very little restriction. The addition of any of these devices to a PC is very worthwhile in cost and time, as in the end this will give the ultimate flexibility and future proofing. All these devices are worth there weight in platinum and combine to create 'the ultimate computer system', with unlimited upgrade options.
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