[mythtv-users] What is a "dual core processor"?

Jim Carter jimc at math.ucla.edu
Thu Dec 4 18:02:54 UTC 2008


On Thu, 4 Dec 2008, Marc Barrett wrote:

> There are older processors which are still technically  "dual core", and I was
> wondering if they would work.  There is the Pentium D, and the "Pentium 
> Dual Core".  As well as many processors from AMD, but I admit that I know
> very little about AMD.  Which of these older "dual core" processor lines
> would work, and how fast of a system would I need?  

I believe the exact nature of the processor(s) is not all that important.  
In one test on very old hardware, a Pentium III "Coppermine" at 1.0GHz was 
just barely able to compress (MJPEG2) a NTSC stream and play it back in 
live TV mode, with rare missed frames.  This is OK for a proof of principle 
but not for production.  Other people report similar performance.  

A Pentium 4 2.4GHz handles the same workload with 35% to 45% CPU 
utilization.  I don't have MythTV data on Core 2 chips but my impression 
for other workloads is that, like AMD chips, they run the clock half as 
fast for the same work product.  There is also the "Core" line (without the 
2) which is slightly older; I don't know its clocking.

I just ran a short benchmark on a Pentium D 3.4GHz.  It runs 3.2 times 
faster than the Coppermine (so it's using old Pentium clocking), but 2 
simultaneous instances of the benchmark run in the same time as a single 
one, meaning that there are 2 independent cores.  For MythTV that means 
that backend NTSC compression and frontend displaying would each settle 
onto a different core.  The machine would be very lightly loaded.

Some or all Pentium 4's have hyperthreading, which means that one core can 
hop between two instruction streams.  On a HT Pentium 4 the test with two 
benchmark processes takes twice as long as with one.  In /proc/cpuinfo the 
HT chip is reported as two processors.  Beware, the processor flags (see 
/proc/cpuinfo) on the Pentium D and Core 2 Duo announce "ht" 
(hyperthreading) which these chips do not actually have.  Or if they do, 
Linux smartly doesn't turn it on.

I hope this clarifies some of the confusion about the Pentium D.

James F. Carter          Voice 310 825 2897    FAX 310 206 6673
UCLA-Mathnet;  6115 MSA; 520 Portola Plaza; Los Angeles, CA, USA  90095-1555
Email: jimc at math.ucla.edu    http://www.math.ucla.edu/~jimc (q.v. for PGP key)


More information about the mythtv-users mailing list