SCSI-3 Reseved Fields and Codes

Tak Asami (Asami asami at
Wed May 4 21:14:21 PDT 1994

Roy Shenfield of Adaptec wrote:
> In summary, it seems to me that making the setting of reserved bits equal
> to zero mandatory, but the checking of the same reserved bits optional 
> could lead to some potential problems.

Excuse me, but I couldn't resist this one....

Since when an arbitrary business decisions become a concern of SCSI
(or any ANSI) standard?
The company C is free to care about the reserved field zero status or not
to care.  If Drive A did not sell for this reason, well, that's that.
That still doesn't sound like a reason for SCSI standard to mandate such
checking.  Drive B didn't violate anything if it did check for the zeros.
That's a drive B feature.

The point is this:
If a standard for interoperability has to assume the other guy may not
follow the prescribed rules, then I bet I can find a way to break that
system no matter what you do for the protection.
And on top of that, the component will be slower and more expensive.
But without making such protection a mandate, you can make your product
slow and expensive if you wanted to without violating the standard.

Tak Asami
Western Digital Corp.
I/O Product Engineering

(714) 932-7621
asami at

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