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

Brian Schott bschott at east.isi.edu
Sun Feb 4 02:09:34 UTC 2007

I  agree.  MythTV might have a relatively small footprint, but it can  
be pretty bandwidth intensive (not to mention having real-time  
constraints if you don't want to drop frames).  Single channel memory  
might have a bigger impact than you think given the number of memory  
copies that are probably going on in the different library layers  
(decoder, filter, etc.)

On Feb 3, 2007, at 11:52 AM, Daniel Kristjansson wrote:

> 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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