Re: SONY or CD-ROM lying about speed?

Mark Lord (mlord@pobox.com)
Sun, 07 Feb 1999 10:44:14 -0500

Thierry Danis wrote:
>
> On Sat, Feb 06, 1999 at 04:37:34PM +0100, Jon K Hellan wrote:
> > I have a SONY 32x CD-ROM CDU771. However, Linux reports it as 14
> > speed. Apparently, FreeBSD does the same.

The PIDENTIFY_DEVICE command is sent to the drive,
and one of the data fields returned is "drive maxspeed"
which in this case the drive sets to "14 x 176KB/sec"
(176KB/sec = 1X or "original" CD speed).

Linux just displays what the drive told it.

> I've seen the same. Running a 'dd' over a complete CDROM
> gives me a transfer rate around 2100 KB/s, which is x14.
> I have a CD-ROM CDU701.

Note that the "maxspeed" only applies to a small zone on the outer
tracks,
which is why cdroms are now advertised as "up to 32x" rather than "32x".
The *average* over the whole drive will be much lower than the maxspeed.

-- 
mlord@pobox.com


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/