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A subset of the SCSI-3 standard, also known as IEEE 1394, Firewire is a new high speed data exchange protocol developed at Apple. Occasionally it is referred to as "serial SCSI" because it is a serial protocol and conforms to SCSI standards as well.

They stated that in a fashion that is, at best, a bit confusing. This draft specification for the SCSI architectural model shows on page 10 a diagram showing that there are several interconnect layers for SCSI, including the classic parallel SCSI bus (SPI), and three count 'em three serial layers, namely Fibre Channel (FC-PH), FireWire ("IEEE 1394 High Performance Serial Bus"), and IBM SSA (SSA-PH), with each interconnect layer having a protocol used to implement SCSI on that layer.

Then there are the SCSI commands, which are mostly if not entirely independent of the interconnect layer and protocol. They can be sent over parallel SCSI, Fibre Channel+FCP, FireWire+SBP, SSA-PH+SSP, {pick your link layer}+IP+TCP+iSCSI, Ethernet+HyperSCSI, or the Serial ATA link layer+serial attached SCSI, and, apparently USB+some way of sending SCSI commands over USB. (There certainly don't seem to be many bit-serial links over which you can send SCSI commands and replies.... :-))

FireWire isn't "SCSI", it's an interconnect over which you can send SCSI commands and replies. It's also an interconnect over which you can send stuff that has nothing to do with SCSI, e.g. IP datagrams (we ignore here the possiblity of IP datagrams containing TCP segments that make up iSCSI PDUs :-)), just as Fibre Channel is an interconnect over which you can send SCSI commands and replies, as well as stuff that has nothing to do with SCSI, e.g. IP datagrams, and just as USB is an interconnect over which you can send SCSI commands and replies, as well as stuff that has nothing to do with SCSI, including network packets.

For SCSI Ultra640 is being hammered out along with SA-SATA. Soon you'll be able to use big cheap SATA drives (or the usual expensive performance SCSI) on a SA-SCSI interface (but not visa versa). SA-SCSI will feature the benefits of SATA and more.

snatched from the site:

What is the difference between Parallel SCSI and Serial Attached SCSI?
Parallel SCSI is a proven enterprise level technology for I/O and device requirements with a twenty-year history of reliability, flexibility and robustness. Parallel SCSI has limited device addressability as well as certain physical limits associated with the nature of its distributed transmission line architecture (performance and distance), plus large connectors that make it unsuitable for certain dense computing environments.

Serial Attached SCSI will leverage the proven SCSI technologies that customers expect in data center environments, providing robust solutions and generational consistency. It will be based on a serial interface, allowing for increased device support and bandwidth scalability, reducing the overhead impact that challenges today's SCSI environments. It will provide easy solutions for systems with simplified cable routing. It will also utilize Serial ATA development work on smaller cable connectors, providing customers a downstream compatibility with desktop class ATA technologies.

Finally, this simplified routing will enable a new generation of dense devices, such as small form factor hard drives, which will enable storage solutions to scale externally where traditional parallel SCSI cannot, due to cabling and voltage challenges.

Is Serial Attached SCSI complementary to or competitive with Serial ATA?
Serial Attached SCSI complements Serial ATA by adding dual porting, full duplex, device addressing and it offers higher reliability, performance and data availability services, along with logical SCSI compatibility. It will continue to enhance these metrics as the specification evolves, including increased device support and better cabling distances. Serial ATA is targeted at cost-sensitive non-mission-critical server and storage environments. Most importantly, these are complementary technologies based on a universal interconnect, where Serial Attached SCSI customers can choose to deploy cost-effective Serial ATA in a Serial Attached SCSI environment.

Of course, no discussion of Serial ATA would be complete without mentioning the answer from the SCSI camp - Serial Attached SCSI. SAS will use the same connector as SATA, but will support longer cable lengths, multiple initiators (if you don't know what an initiator is you don't even belong in this discussion), full SCSI semantics instead of lame-o ATA semantics, etc. Even so, the SAS folks are still ceding the high end to Fibre Channel and talking about three coexisting technologies for the low-end/midrange/enterprise market segments. Sorry, kiddies, but SATA is still low-end.

If there's one mistake you should try not to make more than once in this business, it's that competitors have been standing still since their previous generation. Announcing something brand new and having it be less than half a generation ahead of the competitor's last version is a failure.

They're using the same physical layer as Serial ATA and doing SCSI on top. A new computer industry standard does the opposite of gratuitous incompatibility (gratuitous compatibility?) and probably makes things *more* convenient. What a pleasant surprise!

• Support for the SCSI protocol
• Support for tagged queueing, allowing the drive to multitask. The standard ATA and SATA protocols do not support this yet.
• A single port can connect to multiple drives through an expander (similar to a switch). Currently, SATA is a strict point to point connection.
• Multiple adapters can talk to the same drives.
• Backward compatible support for SATA drives using a tunneled protocol that even allows multiple adapters to talk to the same SATA drive.
• Initial speeds of 1.5 Gb/s and 3Gb/s per port, compared to SATA's 1.5Gb/s per port

Check out: Serial Attached SCSI. This looks to be a superset of Serial ATA. In fact it suggests that a SaSCSI drive would work fine attached to a SerialATA infterface, but not vice versa.

Reposted for those who can't see anonymous messages:

by Anonymous Coward on Wednesday March 20, @10:31AM (#3194064) There is also this web sight. SAS which discusses the future of SCSI and how it will share the same physical connectsions as sATA.

This site has some interesting info to read up on.