Software Write Protect Proposal

Jeff Williams JWILLIAM at
Thu Feb 1 06:51:00 PST 1996

* From the SCSI Reflector, posted by:
* Jeff Williams <JWILLIAM at>

> 1) Making the WP bit in the MODE SENSE header a "writable" bit can result 
> unintentional clearing of write protected condition. Many SCSI drivers 
> always clear these header bits when doing a Mode Sense followed by a Mode
> Select because all of these bits are supposed to be illegal for MODE 
> A bit within a mode page would not have this problem.

What makes this any more "clearable" than a reserved bit in a mode page?  I 
would prefer to see the header bit used since it is already defined to 
indicate that write protect is on.  If a device is in a state such that the 
write protect is on, then it knew that it turned on the write protect and it 
knew how to do it.  Keep the bit where it is at and add a definition for a 
mode select.  When I looked at implementing write protect a long time ago, I 
felt that this was the most logical mwthod for turning it on and off.  Most 
people just to a read/modify/write on the pages and could/should do the same 
for the header.

Jeff Williams
Jeffrey L. Williams                                   Office: (507) 286-7589
Western Digital Rochester                                Fax: (507) 286-7528
Enterprise Storage Group                      e-mail: jwilliam at

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