The latest SCSI-revision is able to provide up to 160 MB/s. Some people may wonder how this is supposed to work with a normal PCI-card, which has a bandwidth limitation of 133 MB/s. The answer is simple. Most Ultra160 cards are only available as 64 Bit PCI cards. A few Ultra160 cards are available as 32 Bit models.
Luckily, every 64 Bit card can also be used in 32 Bit PCI slots - as long as there is no component in the card's way.
You may wonder what's the use of a bandwidth of 160 MB/s when even the fastest SCSI hard drives can only supply a data stream of up to 40 MB/s. You've got to remember that SCSI is a bus system with which you can daisy-chain 7 or 14 devices. Those devices are all sharing the SCSI-bandwidth. Therefore 160 MB/s can easily be used up with a RAID that consists of four high-end hard drives. Adding more hard drives to this RAID would already require a higher bandwidth.
The performance of 160 MB/s is be achieved using a technology called 'Double Transition Clocking'. It's the same basic idea which is used with AGP2x, double data rate memory or the Athlon's double-pumped system bus. Data is transferred at both the rising and the falling edge of a bus clock cycle, thus doubling the transfer performance without increasing the bus clock.
There are some other innovations that Ultra160 takes advantage of, which are making this standard faster and more secure than all prior versions. The explanation of those would go too far, so I decided to skip this part for the time being.
If you want to know more, please check at IBM's website .
Similar information can also be found on Adaptec's website .