🚀 go-pugleaf

In article <31465@mips.mips.COM> rr@pika.mips.com (Robert "Bob" Rodriguez) writes:
>Can anybody comment on whether SCSI-2 is dead and disk manufacturers
>are going yo jump to something called SCSI-3. I have heard rumors.....
>

As with most rumors, this one is more wrong than right.  The disk manufacturers
are working on implementing SCSI-2, but there is some confusion over the
cables.  The cable issue probably fueled this rumor.

SASI and SCSI-1 defined a single 50-conductor cable which transfers 8-bit
data.  The other signals are used for control, grounds, etc.

SCSI-2 defined an optional second cable to allow another 8 or 24 bits of data
to achieve a total of 16 or 32 bits.  This option is referred to as wide SCSI.
The new cable is called the B cable and the original cable (same as SCSI-1) is
called the A Cable.  The B Cable uses 68-conductors when fully populated for
32-bits.  It uses 68-pin connectors even when used for 16-bits.

After SCSI-2 was forwarded out of X3T9.2 (the committee that developed it), a
proposal for doing 16-bit data transfers with only one 68-conductor cable was
received.  This cable has become known as the P Cable.  (I'm not sure why
George Penokie called it the P Cable -- one can only guess :-) 

Of course, the disk manufacturers are much more interested in doing 16-bit
devices with one cable than with 2 cables.  Especially since the committee
has found a clever way of permitting compatibility with 8-bit devices:  The
middle conductors of the P Cable are the same as in the SCSI-1/SCSI-2 A Cable.

I won't bore you with further talk about the Q Cable (P+Q= 32 bits) or the
S Cable (32-bits, with a centered P Cable), but suffice it to say that the
committee has plenty of ideas! :-)

All this gets even more complicated because the committee still has not come
to grips with the scope of the SCSI-3 project and because SCSI-2 is not
beyond change.  As chairman of the SCSI committee, I have received a public
review comment from Western Digital saying we should remove the B Cable from
SCSI-2 and consider adding the P Cable.  I understand that Micropolis plans
to submit a similar public review comment just requesting that the P Cable
be added as an appendix to SCSI-2.  (This means it is not mandatory, but then 
wide SCSI isn't either.)

The committee will address these comments at our Dec. 4-5 meeting.  It should
be real fun ;-).

In any case, wide SCSI is only part of SCSI-2 -- but a tangible part.  I 
believe the disk manufacturers will use the P Cable approach, but otherwise
follow SCSI-2 PROVIDED they need 16-bit data transfers.  If you only need 
8-bit data, then the A Cable is fine...

-- 
John Lohmeyer         J.Lohmeyer@Wichita.NCR.COM
NCR Corp.             uunet!ncrlnk!ncrwic!entec!jlohmeye
3718 N. Rock Rd.      Voice: 316-636-8703
Wichita, KS 67226     SCSI BBS 316-636-8700 300/1200/2400 24 hours