Optical Drive and Library SCSI-2 Command Reference

SCSI-2 Drive Command Set
Mode Select Command (15H)
Chapter 22-38
MF The Multiplication Factor bit is set to 1 and cannot be
changed. This bit is used with the Minimum and
Maximum Pre-fetch fields during READ operations. If
this bit is set to 0 by the MODE SELECT command, a
CHECK CONDITION status is returned with the sense
key/additional sense code set to ILLEGAL REQUEST/
Invalid Parameter List.
Disable Pre-fetch
Transfer
Length This field sets the threshold value for pre-fetching data
during reads. If the number of blocks to be read is
greater than this value, no pre-fetching occurs.
Minimum
Pre-fetch The default value is 1 and cannot be changed. If this bit
is set to 0 by the MODE SELECT command, a CHECK
CONDITION status is returned with the Sense Key/
Additional Sense Code set to Illegal Request/Invalid
Parameter List. Since the MF bit is 1 and the Minimum
Pre-fetch bit is also 1, the Minimum Pre-fetch size is
equal to the READ transfer length. This field does not
affect the operation of the drive.
Maximum
Pre-fetch The default value is 1 and cannot be changed. If this bit
is set to 0 by the MODE SELECT command, a CHECK
CONDITION status is returned with the Sense Key/
Additional Sense Code set to Illegal Request/Invalid
Parameter List. Since the MF bit is 1 and the Maximum
Pre-fetch bit is also 1, the Maximum Pre-fetch size is
equal to the READ transfer length. This field does not
affect the operation of the drive.
Maximum
Pre-fetch
Ceiling The Maximum Pre-fetch Ceiling field does not affect the
operation of the drive and can be set to 32 or 64. If
another value is set, a CHECK CONDITION status is
returned with the Sense Key/Additional Sense Code set
to Illegal Request/Invalid Parameter List.