[mythtv-users] CPU power for digital tuners

Jarod Wilson jcw at wilsonet.com
Fri Jul 9 20:27:29 EDT 2004

On Friday 09 July 2004 17:01, Dylan Egan wrote:
> > On the other hand, general throughput (e.g. PCI bus, HDD) might become a
> >problem. Here in Oz, SD broadcasts are about 6Mbit/s, and I think HD are
> >10-12. If you've got a few cards recording HDTV at the same time, you'll
> >want to make sure you've got a pretty quick disk subsystem.
> >  
> Hrmph yeh I didnt really consider that. Im using that machine as a file
> server too, it used to be a mail/web server too, but I moved that to
> another machine. Maybe I can have 2 machines splitting 4 cards or so, so
> 2 in each. Im running 1 SATA drive at the moment.

Typical US ATSC HDTV streams are usually 19.2 Mbps (though they can be 
greater). Any reasonably new hard drive has a sustained throughput threshold 
magnitudes greater. SATA has a theoretical peak of 150MB/s. Low-balling it, 
sustained transfers might be in the 60MB/s range, which still translates to 
480Mbps. So you can write several HDTV streams at once. I know someone who 
has 3 pcHDTV cards that has no problem recording 3 streams at once on a 
single 5400rpm drive.

In short, if you're talking 10-12Mbps streams, your single SATA drive 
shouldn't have a problem handling all four cards. That'd be a peak throughput 
requirement of 48Mbps, which is hardly going to make the drive sweat. At 
least theoretically. (Some of the Linux SATA drivers still absolutely suck).

Jarod C. Wilson, RHCE
jcw at wilsonet.com

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