Types of SCSI

Can someone explain the different types of scsi. Like SCSI II, 160, 320 and so on. Seems like there are a lot of standards for them. Which one is widely used?

SCSI is much like IDE, it has a progression but Ill let someone else explain.
http://www.scsilibrary.com/standards.html
http://www.pcguide.com/ref/hdd/if/scsi/std/
http://www.scsita.org/terms/SCSI_Overview.html
From a google search.

Here's a decent start.

Interfaces:

SCSI interfaces come in several varieties grouped by their maximum theoretical bandwidth and width of the bus. Interfaces include:

SCSI-1 5MB/Sec 8 bit SCSI Bus
SCSI-2 5MB/Sec 8 bit SCSI Bus
SCSI-2 Fast 10MB/Sec 8 bit SCSI Bus
SCSI-2 Fast Wide 20MB/Sec 16 bit SCSI Bus
SCSI Ultra 20MB/Sec 8 bit SCSI Bus
SCSI Ultra Wide 40MB/Sec 16 bit SCSI Bus
Ultra2 Wide 80MB/sec 16 bit SCSI Bus
Ultra160 Wide 160MB/sec 16 bit SCSI Bus
Ultra320 Wide 320MB/sec 16 bit SCSI Bus

The last four in the main list are the most commonly used interfaces.

Fiber channel drives and adapters are also available, but are too expensive for anything other than the enterprise server market.

Unlike DMA modes for the ATA specification (with the exception of PIO mode devices), connection of compatible lower speed devices will cause the interface to lower its performance to the level of the slowest device. For example, use of narrow SCSI-2 devices on a Ultra2 Low Voltage Differential (LVD) port will cause the entire bus to run at the SCSI Ultra 20MB/sec level. Very few people still use the narrow bus (8 bit), but devices are still available, most commonly in optical drives.

The number of devices, which can be attached to any channel, varies with the type of controller used and usually the cabling requirements. Narrow (8 bit) controllers can support up to 7 devices and the controller. Wide (16 bit) controllers can handle 15 devices and the controller. The reason that this is noted per channel is due to the many multi channel controllers in use. Controllers can commonly come with 4 or more channels, particularly in higher end RAID controllers.

The devices on a SCSI chain use identification numbers rather than the master/slave configuration of IDE specifications. The devices are numbered from 0 to 7 on narrow interfaces and 0 to 15 on wide interfaces, with ID 7 typically being the controller on both bus styles. For a drive to be bootable, it needs to be ID 0 on most controllers. ID also can determine the priority of the devices with the lower numbers having increased priority.

Connections:
Over the years, SCSI has used a variety of connection styles. This has added some confusion, since there are adapters for the various types of internal and external cabling. Currently, the cabling that you are most likely to see is the 68 pin internal type. You may find that drives are listed as SCA. These drives use 80pin connectors and require either backplanes or adapters to attach to the 68 pin cabling.

Hope this helps.

That is very well written. I hope someone might think about taking your post and making it a sticky since there isn't one on SCSI. In a nutshell it's almost the perfect post

Thanks, I had started writing something towards that end and never got a chance to complete it.