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Quad-core CPU and WinRAR question

mikeymikec

mikeymikec

Lifer
WinRAR on my machine (with an Athlon II X4) never seems to use all the CPU time, but rather 50-75% of it, even on the benchmark. Does anyone else notice this?

I'm using 4.01 64-bit on Win7.
 
AFAIK, it's rather common for all multithreaded apps. I don't know of any that can fully utilize each core. For example, I recall awhile back someone compared a C2D to a similar-speed C2Q with a multithreaded app, and saw about a 35% increase in performing the task...and wondered why it wasn't at least a 75% increase.

It primarily depends on the amount of effort the developer puts into it. Plus, I think there are differing results between AMD and Intel procs, and most devs put more effort toward Intel results. I think another dependency is the speed of your RAM.
 
On my computer at least, 7zip uses 90-100% during the benchmark. This is a shot in the dark but I think that since file compression is cache-reliant, the Athlon II's lack of L3 might be bottlenecking the process.
 
It depends on how much effort has gone into parallelising the software, and also how parallel it can be made.

Some types of software simply cannot be made to benefit from multiple cores/threads to any significant degree (these algorithms are called "inherently serial" and it is mathematically impossible to break the problem down into individual threads because each calculation to be performed relies on the answer from the immediately preceding calculation), the classic example of this is ZIP compression.

Others are "embarrassingly" parallel (like video encoding or 3D rendering) and scale almost perfectly.

Most software is somewhere in the middle. The RAR algorithm scales very well for a general-purpose data compression tool, but because of the fact that compression is, to a large part, a serial process - it cannot be effectively parallelized onto a large number of cores.
 
I just tried the 7-zip benchmark and got 90 - 100% CPU usage (though with an occasional sawtooth effect on the graph).
 
Though I havent upgraded (3.7x) version WRAR, I have found out that memory speed and bandwidth make a difference as well, Im using a AII X4 640 and it will hold 66-75% with DRR2 1066, It was significantly lower with 800.
 
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