The origin of SCSI [WAS:RE: The origin of the phrases ATA and IDE ]

Jerry Weiss jsw at
Thu Oct 5 20:39:34 CDT 2017

The DK Driver for VMS versions around 5.x definitely had a problem with non-DEC disks.  6.X and greater were slightly more forgiving.

The specifics are summarized in a note from Ralph Weber in!search/SCSI$20Mode$20Page$20Requirements$20$20axp/comp.os.vms/RAaUpP_XXEw/BWn64YZYwBQJ .  

I don’t think there is list of non-DEC disks in the driver as it instead checked the SCSI Mode bits and other disk configuration settings.   There is a list (table) for DEC Drives (idiosyncrasies?) and another SCSI2 Tagged Queuing devices requirements used for Clusters in the driver.


> On Oct 5, 2017, at 6:23 PM, Peter Coghlan via cctalk <cctalk at> wrote:
>> The biggest problem you had was the requirement to assert ATN when selected properly.� Later the tag queuing caused huge headaches as manufacturers implemented that feature.
>> It eventually was made mandatory for the most part by linux, and perhaps Windows requiring the tag queuing drilled own to the lowest level of the system's use of the disk.  The capability to do that, or fake it is required to allow the kernel to queue commands to run, and have the OS continue to run till command completion.
> I recall VMS having issues with SCSI disks which claimed to do tag queueing
> (and bad block replacement) but didn't do it right, before I'd even heard
> of linux.
> Customers complained that VMS refused to work with commodity SCSI disks
> and thought that it was a conspiracy to get them to buy expensive DEC branded
> disks.  DEC claimed that only the disks with their firmware did tag queueing
> and bad block replacement correctly.  The VMS SCSI driver supposedly had (has?)
> a list of specific disks known to mess up which it would refuse to bring
> online.
> I wasn't well up on Sun but I expect the same issue existed there too.
> Regards,
> Peter Coghlan.

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