Hardware Reference
In-Depth Information
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 in-
crease 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
drivesarecapableof;however,high-performanceSSDs(Solid-StateDrives)withaSATA
6Gbps interface can achieve and even exceed that level of performance.
Note
AlthoughUSB3.0isfasteronpaperthaneSATA,inrealityeSATAisstillfasterandmoreef-
ficient for connecting external drives. This is because USB adds overhead to the connection,
andanyexternalUSBenclosurestillincorporatesSATAinternallyforthedriveinterface.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.
The primary enhancements in USB 3.0 include the following:
• Dedicated IN and OUT lanes with four additional wires (plus ground) allowing full-
duplex operation (reading and writing at the same time).
• Increased power available for bus-powered devices, 900mA (4.5W) versus only
500mA (2.5W) in USB 1.1/2.0.
• Aggressive power management; links go to low-power states when idle.
• The host schedules all transactions (no polling).
• Both hosts and devices transmit only when they have data.
