X3T9.2/87-84



To:       John Lohmeyer -- Chairman X3T9.2

From:     Anthony Kozlowski

Subject:  Peripheral Device Type for Direct Access Tape Devices

Date:     May 18, 1987



There is a need to create another Periperal Device Type code, 
as reported by the Inquiry Command.  This new Device Type is 
a Direct-Access Magnetic Tape Device.  This new device type 
can be characterized by the following statements:

     1. The device is a block-oriented tape drive;
     2. Each block on the device is individually addressable;
     3. Each block on the device is individually modifiable;
     4. The device responds to the Direct-Access SCSI command 
        set;
     5. The data concept of the device is fixed-block-size, 
        contiguous, error-free data to the host;
     6. Block sizes are typically larger than for Disk 
        devices (1K, 4K, 32K vs. 512 bytes);
     7. Because the device is a tape device, access time is 
        much slower as compared to a Disk device;
     8. Before reading or writing can take place, the medium 
        used in the device must be formatted;


Since this device is a mix of characteristics of other 
devices, it is important for a self-configuring system to 
recognize this device as being different from other like-
responding devices in the system.  To that end, I recommend 
that the Peripheral Device Type Code for this device be 
different than the standard Direct-Access Device Code.

Specifically, I recommend that the Peripheral Device Type 
Code for Direct Access Magnetic Tape Devices be:   10h.

This code value was chosen to conform to the value of 
implementation of current Direct-Access Magnetic Tape 
devices.
In order to effect this change, the following are the changes
that should be made to the SCSI-2 document, X3T9.2/86-109 
Rev. 1, dated April 15, 1987:


p. 7-13  Table 7-11: Peripheral Device Type

     Code           Description
     --------------------------------------------------------
      0Bh - 0Fh     Reserved
      10h           Direct Access Magnetic Tape device
      11h - 7Eh     Reserved


I do not feel it is necessary to specifically detail this 
device type label wherever the Peripheral Device Type name is 
listed (ie, as part of each command), since all of the 
Direct-Access commands potentially apply to Direct-Access 
Magnetic Tape devices.

Thank you for your consideration in this matter.

Sincerely,




__________________________

A. Kozlowski