Date: Thu, 2 Sep 1999 01:40:38 +0200 (CEST) From: Oliver Fromme <olli@dorifer.heim3.tu-clausthal.de> To: freebsd-current@FreeBSD.ORG Subject: Re: HEADS UP! ATA driver (atapi DMA).. Message-ID: <199909012340.BAA03349@dorifer.heim3.tu-clausthal.de>
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Daniel O'Connor wrote in list.freebsd-current:
> On 31-Aug-99 Kevin Street wrote:
> > > Well 2MB/sec == 14x CDRom drive. Is it a 14x CDRom drive? CDRom
> > > drives are typically limited to how quickly they can get data off
> > > the platter. A faster bus transfer will not improve that.
> > I should have mentioned that ... it's a 32x cdrom. dmesg says it
> > claims to be able to do 5515 KB/sec.
>
> Which is slightly more correct..
> 32x = 32 * 150 = 4800 kb/s
>
> 1 spin = 150kb/sec
The raw mode2 data rate is 176400 bytes/sec (not counting
subchannel information, which is normally not transferred
along with the raw data anyway):
176400 * 32 / 1024 = 5512.5 Kbyte/sec.
That number is derived from the throughput of CD audio data:
176400 bytes/sec = 44.1 kHz * 2 channels * 2 bytes/sample.
(There are 75 sectors per second with 2352 bytes each.)
Don't know where those 5515 come from... Maybe they
rounded generously... ;-)
Regards
Oliver
--
Oliver Fromme, Leibnizstr. 18/61, 38678 Clausthal, Germany
(Info: finger userinfo:olli@dorifer.heim3.tu-clausthal.de)
"In jedem Stück Kohle wartet ein Diamant auf seine Geburt"
(Terry Pratchett)
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