| USB
(universal serial bus) 1.0 was introduced in 1995 and USB 1.1 came along a couple of years
later. As mentioned in last
month’s article, it has not had a significant impact on the marketplace yet.
USB 2.0 is expected to reach the
marketplace in the fourth quarter of this year with broad deployment in 2001. With the
arrival of USB 2.0, I believe we will see a rapid disappearance of conventional serial,
parallel, and game port devices and the IDE (integrated drive electronics), PCI
(peripheral component interconnect), and AGP (accelerated graphics port) technologies.
In some applications USB 2.0 will also
compete with the popular SCSI (Small Computer Systems Interface) technology.
USB’s biggest attraction is the
ease with which multiple and various peripheral devices can be connected and unconnected.
Attaching a USB peripheral to a USB hub is as easy as plugging a telephone line into a
wall jack.
USB 1.1 is capable of two different
communication speeds. In low-speed mode it transfers data at a rate of 1.5 megabits per
second (mbps). In high-speed mode the transfer rate is 12 mbps. The bus automatically
shifts speeds to match the speed of the peripheral. Keyboards, mice, and joysticks are
examples of low-speed devices while printers, scanners, and zip-drives are examples of
high-speed devices.
USB 1.1 is much faster than a regular
serial port (RS-232) which communicates at a rate of approximately .25 mbps. Thus, USB is
six times faster than RS-232 in low-speed mode and 48 times faster in high speed mode.
USB 2.0 will increase the throughput
speed over USB 1.1 by a factor of 40. Its projected transfer rate of 480 mbps or 60
megabytes (8 bits=1 byte) per second (MBps) will be close to that of the fastest IDE hard
drives which have a transfer rate of 66 MBps.
USB won’t be as fast as SCSI. Fast
SCSI-2 moves data at up to 80 MBps and Ultra SCSI-3 is capable of speeds up to 160 MBps.
USB 2.0 will be closer than v1.1 to the speeds of SCSI-3 and will therefore be a viable
replacement in some cases for SCSI because of ease of configuration.
USB’s biggest attraction is the
ease with which multiple and various peripheral devices can be connected and unconnected.
SCSI can be exasperating if the devices
and controllers aren’t perfectly addressed and terminated. Because of it superior
speed, SCSI will retain its dominance as the technology of choice for large server hard
drives and tape drives. SCSI speeds will continue to increase and it is not likely that
any technology will surpass it.
This year, the SCSI Trade Association
adopted a new SCSI technology plan that will provide up to 640 MBps performance.
Predictions that USB 2.0 will replace SCSI seem unlikely to me. Most network
administrators will choose throughput speed over ease of configuration and administration.
To take advantage of USB 2.0, your
computer must have a motherboard equipped with at least one USB 2.0 port on board. These
motherboards should be available by the end of the year. USB 2.0 will be fully forward and
backward compatible with other versions and will support a mixture of v2.0 and v1.x
devices on the same hub.
All USB 1.1 cables and connectors will
support the higher speeds of USB 2.0. A USB 1.1 hub will work with USB 2.0 but not at
v.2.0 speeds.
Replace the hub with a new one and
daisy chain the v1.x hub to the v2.0 hub for expanded device capacity. Plug v.1.x devices
into the v.1.x hub and use the v.2.0 hub ports for v.2.0 devices.
The USB 2.0 host
negotiates the communication speed with each device based on the speed of the device.
Device addressing and configuration is done automatically by the host for true plug and
play functionality.
Will it really
work? Look for the answer in a follow up article around this time next year.
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