[mythtv-users] HD Woes (so close to working, dual-channel RAM question)

Daniel Kristjansson danielk at cuymedia.net
Sat Feb 3 16:52:08 UTC 2007

On Sat, 2007-02-03 at 08:41 -0700, Brian Wood wrote:
> On Feb 3, 2007, at 8:10 AM, Nate Crosno wrote:
> > So my current question is how much of a difference does dual  
> > channel memory
> > make on a Mythtv system?  I am an idiot and did not realize I  
> > actually had a
> > 1gb and a 512mb stick and not 2x512.  In the bios on startup, it  
> > says it's
> > running in single channel mode.
> >
> I suspect it would not make much if any difference, Myth is not a  
> memory access intensive application.

Memory bandwidth of playback using deinterlacer:
 1088 * 1920 * 4 * 3 * 30 = 752 MB/second

Memory bandwidth of single channel DDR400:
 3200 MB/second

But that being said, I ran my computer for a week last year
with single channel memory due to a RAM chip failure and
the whole computer was agonizingly slow. (Same amount of RAM,
I had extra SIMMs, just not a combo that could be used in a
dual-channel configuration). Dual channel RAM on a processor
capable of handling the bandwidth, like the AMD 3500+ or any
P4 or later, effectively doubles the speed of your computer
when doing memory intensive things like running gcc, loading
a program into core, etc.

With MythTV I suspect that it would give you less than a 12%
performance boost @ 1080i, since only about 24% of your
playback time is dedicated to memory copies.

-- Daniel

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