On 23 Jul 98 at 10:16, Ubiratan C. Peleteiro wrote:

> What is the basic diferences between SCSI-1, SCSI-2 and SCSI-3?

  SCSI-1 and SCSI-2 both use 50-pin connectors, but are rated for
different speeds.  External SCSI-1 devices use a Centronics-style
connector (like the 36-pin connector on many printers); external
SCSI-2 devices may also use that, but are more likely to use a
D-shaped (trapezoidal) high-density connector.
  Internal SCSI-2 devices use a 50-pin ribbon cable.  I don't think
I've ever seen an internal SCSI-1 device, but I'd expect them to do
the same.

  "SCSI-1" and "SCSI-2" are names of official standards.  As far as I
last heard, "SCSI-3" was not, but was often being used by salespeople
to refer to Wide SCSI, which uses a D-shaped high density 68-pin
connector, both internally and externally.

> How can i identify a HD and an interface with this specification,
> if it isn't in the manual?

  There are three common interfaces on SCSI HDs:

- 50-pin ribbon connector = SCSI-2

- 68-pin "D" connector = Wide/UtraWide (or Differential[*])

- 80-pin ribbon connector = "SCA" wide connector with integrated
power; SCA-to-68-pin adapters are available.

> Are they compatible? Can i use a SCSI-3 HD on a SCSI-1 interface,
> or a SCSI-1 HD on a SCSI-3 interface?

  You can get an adpater that will fit the 68-pin connector on a wide
drive and connect it to a 50-pin (SCSI-1/SCSI-2) bus; in that case,
you've paid for performance you can't use (and paid extra to not use
it).
  You can get adapters to connect 50-pin devices to a 68-pin bus.
Good ones will terminate the lines they don't use -- this has
implications for physical ordering of devices on the bus.

> I have a DEC2000 AXP server with on-board SCSI adaptor on my
> network and i want to put a new HD but i can't identify the
> interface specification.

  See

http://marvelgirl.dmc.com/acornsw.com/WebRoot/tech-notes/00000000.stml

I also found a list which includes "wide SCSI controller" as an
optional add-on, so odds are good that what's built in is 50-pin
only.

David G