Moin Andrew,

24.02.95 04:57, you wrote a message to Mike Bilow:

 MB>> OS/2 does not really know about sectors per se.  At a low level, OS/2
 MB>> uses a SCSI-like model for storage where blocks are allocated in some
 MB>> native size for the media and sequentially numbered beginning with
 MB>> zero.

 AC> So presumably... the kernel asks to read (for example) a particular 
 AC> block based on its block number, and the disk driver
 AC> converts this into a cylinder-sector-head address which it
 AC> thens asks the drive controller itself to
 AC> find? 

The filesystem driver asks DMD for a particular block number. 
DMD calls an ADD and provides this block number. The ADD may translate this
block number to Cylinder-Head-Sector or use it directly depending on the
drive controller interface. MFM, IDE ADDs would translate, SCSI ADDs would
not.

Exceptions:
- The ADD may request the DMD to use CHS addressing (flag per adapter).
This flag is set in IBM?FLPY.ADD.
- There may be filter drivers between DMD and ADD. Filter drivers are
allowed to change anything in the request block (consider a RAID.FLT which
stripes data blocks over several disks).

Bye,
	Vitus

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