SCSI = old-school non-mainstream interface. But I'm sure you knew that.
SCSI-3 isn't native on any Mac, which includes all versions called "Ultra", which in general means all speeds 40 MB/s or higher, but SCSI-3 devices are fully backward compatible with SCSI-2 and SCSI-1.
Then there are the physical interfaces.
"Narrow SCSI" is the internal 50-pin connection that is standard on every desktop Mac from the SE through the beige G3.
"Wide SCSI" is either the standard "desktop-style" 68-pin connection, or the server-style 90-pin "SCA" connection which includes data, power, and 'config' (aka SCSI ID jumpers) on one connection for use in hot-swap bays. Both Wide SCSI connectors can be converted to a narrow 50-pin connector with a simple adapter board. (I ran a 9 GB, 10,000 RPM 80-pin SCA Ultra160 drive in my SE/30 for a while.)
SAS is "Serial Attach SCSI", which is the SCSI command set over a serial connection rather than a parallel connection. It is very similar in concept to the PATA->SATA conversion. (And is, in fact, compatible with SATA devices.) SAS is the currently in use version of SCSI. Older parallel SCSI devices can be converted to run on SAS with a (not cheap) adapter, but I haven't yet seen an adapter to let SAS devices work on parallel SCSI (although it is theoretically possible.)
Another SCSI variant? Firewire. Yup, Firewire is SCSI. It's another "serial" implementation of SCSI, similar to SAS, although much older. And yes, SCSI devices can be converted to Firewire with fairly simple adapters. (I have one lying around somewhere, used it to use my Jaz drive on my Power Mac.)
The big problem with using newer server-grade Ultra-something SCSI drives in older Macs is power usage and heat. The drives in the earliest SCSI Macs are slow. Some were as low as 3500 RPM. That didn't draw much power, or generate much heat. (A Connor 20 MB drive of the kind used in the SE ran at 3500 RPM, had a single platter, and drew 4.2 Watts at load.) A newer server-grade drive, the Seagate Cheetah 15K.3, runs at 15,000 RPM, has four platters, and draws 12.21 Watts at idle. That extra power means a lot of extra heat. (When I used my 9 GB 15,000 RPM drive in my SE/30, I had a second power micro power supply powering it, and ran with the cover off.)
SCSI-3 isn't native on any Mac, which includes all versions called "Ultra", which in general means all speeds 40 MB/s or higher, but SCSI-3 devices are fully backward compatible with SCSI-2 and SCSI-1.
Then there are the physical interfaces.
"Narrow SCSI" is the internal 50-pin connection that is standard on every desktop Mac from the SE through the beige G3.
"Wide SCSI" is either the standard "desktop-style" 68-pin connection, or the server-style 90-pin "SCA" connection which includes data, power, and 'config' (aka SCSI ID jumpers) on one connection for use in hot-swap bays. Both Wide SCSI connectors can be converted to a narrow 50-pin connector with a simple adapter board. (I ran a 9 GB, 10,000 RPM 80-pin SCA Ultra160 drive in my SE/30 for a while.)
SAS is "Serial Attach SCSI", which is the SCSI command set over a serial connection rather than a parallel connection. It is very similar in concept to the PATA->SATA conversion. (And is, in fact, compatible with SATA devices.) SAS is the currently in use version of SCSI. Older parallel SCSI devices can be converted to run on SAS with a (not cheap) adapter, but I haven't yet seen an adapter to let SAS devices work on parallel SCSI (although it is theoretically possible.)
Another SCSI variant? Firewire. Yup, Firewire is SCSI. It's another "serial" implementation of SCSI, similar to SAS, although much older. And yes, SCSI devices can be converted to Firewire with fairly simple adapters. (I have one lying around somewhere, used it to use my Jaz drive on my Power Mac.)
The big problem with using newer server-grade Ultra-something SCSI drives in older Macs is power usage and heat. The drives in the earliest SCSI Macs are slow. Some were as low as 3500 RPM. That didn't draw much power, or generate much heat. (A Connor 20 MB drive of the kind used in the SE ran at 3500 RPM, had a single platter, and drew 4.2 Watts at load.) A newer server-grade drive, the Seagate Cheetah 15K.3, runs at 15,000 RPM, has four platters, and draws 12.21 Watts at idle. That extra power means a lot of extra heat. (When I used my 9 GB 15,000 RPM drive in my SE/30, I had a second power micro power supply powering it, and ran with the cover off.)