SET READ AHEAD comments and questions

keiji_katata at post.pioneer.co.jp keiji_katata at post.pioneer.co.jp
Mon Jul 24 21:06:20 PDT 2006


* From the T10 Reflector (t10 at t10.org), posted by:
* keiji_katata at post.pioneer.co.jp
*
Hi Henry,
-----
if a VOB file transition skipped some space, the 1x drive
would be unable to continue to offer seamless playback without a method
for the PC player software to indicate this transition point.
-----
This is not correct. Many CE players use (had used) 1X playback speed reader
unit. DVD Video format allows such 1X players to play multi-angle view back
as
seamless without special buffer control on Reader drive.
SET READ AHEAD command was prepared to guarantee the seamless playback with
high
overhead/low performance PC system. At that time, PC system used pure PIO
mode
data transfer. CPU read a word from ATAPI port, wrote the word to MPEG2
decode
module. 5.1ch audio decode, Navigation control and DVD CSS decode were done
with
PIO data transfer too.
On new media formats, 1X data transfer speed should have some margin as well
as
DVD Video format. And already PC drives have 2X data reading speed on the new
media formats. So there is no problem.
New media/video formats use Full file system. Direct sector access scheme
that
is used by DVD Video may not be able to used for the new media/video formats.
Does Live UDF support IOCTL_STORAGE_SET_READ_AHEAD to read files?
Best regards,
Keiji Katata
PIONEER CORP.
"Henry Gabryjelski" <Henry.Gabryjelski at microsoft.com>@avc-pioneer.com on
2006/07/19 07:03:39
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bcc:
$B7oL>(B:  SET READ AHEAD comments and questions
Microsoft has some questions regarding the current attempt to obsolete
the SET READ AHEAD command.  This command is currently exposed in
Windows XP (and later) via IOCTL_STORAGE_SET_READ_AHEAD and
IOCTL_DVD_SET_READ_AHEAD.
Our understanding is that this command was created for the first (1x)
DVD-ROM drives so that PC player software would be able to optimize the
drive's read-ahead cache for DVD playback.  In particular, most
read-ahead cache on drives at that time would read ahead linearly.
Unfortunately, if a VOB file transition skipped some space, the 1x drive
would be unable to continue to offer seamless playback without a method
for the PC player software to indicate this transition point.
Clearly this optimization is not required any longer for the current
DVD-ROM drive market, as speeds for the drives are now at least 8x read
speed for all drives and can maintain (or "catch up") seamless playback
without this optimization.  However, it seems that this optimization may
once again be required for any new format (i.e. the new blue laser disc
formats) which has non-CE hardware produced at 1x speed ("1x drive A/V
stream" issue).
Please help us to understand the reasons why this command has been
requested to become obsolete.  In addition, if the above "1x drives A/V
stream" issue is already mitigated by other factors, please include this
in the reply.
Thank you,
Henry Gabryjelski
Microsoft Corporation
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