Hardware Reference
In-Depth Information
will not use separate IRQs as they might if each was connected over a separate interface.
USB 3.0 (SuperSpeed USB)
USB 3.0 (also called SuperSpeed USB) offers performance and bandwidth that is more than 10 times
the performance of USB 2.0 and yet is backward compatible with existing USB 1.1 and 2.0. In
addition, USB 3.0 is optimized for lower power consumption and improved protocol efficiency (less
overhead).
On September 18, 2007, Intel announced both the formation of the USB 3.0 Promoter Group and the
development of the USB 3.0 interface, which had already been well underway. The initial members
of the group included Intel, HP, Microsoft, NEC, NXP, and Texas Instruments. The final USB 3.0
specification was released on November 17, 2008.
The main feature of USB 3.0 is an increased transfer speed of 5Gbps (500MBps), thus significantly
reducing the time it takes to move data.
Table 14.6
shows the time it takes each version of USB to
transfer the amount of data contained in popular media, including a music CD ripped as 320Kbps
MP3 files, a standard definition movie, and a high definition movie. These numbers point to the actual
or effective transfer rates of USB, accounting for protocol overhead. From these numbers, you can see
that USB 2.0 is about 40 times faster than USB 1.1, and USB 3.0 is more than 10 times faster than
USB 2.0. An important consideration for the design of USB 3.0 was the time it takes to transfer high
definition movie content, which is about 14 minutes using USB 2.0. Knowing that people would be
highly unsatisfied with that level of performance, USB 3.0 was designed to increase bandwidth so
that a transfer of that type would take just over a minute.
Table 14.6. Time to Copy Media Using USB 1, 2, and 3
It is interesting to note that the level of actual or effective performance indicated by Intel for USB 3.0
(transferring 25GB in 70 seconds) is equal to approximately 360MBps in effective throughput
(including overhead), which compares to about 32MBps maximum effective throughput for USB 2.0.
This is significantly faster than most magnetic storage drives are capable of; however, high-
performance SSDs (solid-state drives) with a SATA 6Gbps interface can easily achieve and even
exceed that level of performance.
Note
Although USB 3.0 is faster on paper than eSATA, in reality eSATA is still faster and more
efficient for connecting external drives. This is because USB adds overhead to the connection,
and any external USB enclosure still incorporates SATA internally for the drive interface. For
this reason many people are in no rush to replace eSATA connected external drive docks and
enclosures with newer and more expensive USB 3.0 versions.
In the future it is expected that both hard drives and especially flash or solid-state storage devices
such as media players or flash drives will experience dramatic improvements in performance, and
USB 3.0 is designed to be capable of meeting the demands of these products.
