[OS X TeX] multi cores

Peter Dyballa Peter_Dyballa at Web.DE
Sun Dec 13 14:40:19 CET 2009

Am 13.12.2009 um 12:26 schrieb Josep Maria Font:

> According to Apple's Tech Specs page, for the 27" iMac there are,  
> besides the Core 2 Duo processors, the following two processor  
> configurations:
> • 2.66GHz quad-core Intel Core i5 processor with 8MB shared L3  
> cache; Turbo Boost dynamic performance up to 3.2GHz
> • 2.8GHz quad-core Intel Core i7 processor with 8MB shared L3 cache;  
> Turbo Boost dynamic performance up to 3.46GHz; Hyper-Threading for  
> up to eight virtual cores

The names i5 and i7 just mean that the latter uses hyper-threading,  
i.e., the ability to tell the system it has twice as much cores, the  
i7 has one more step (5) of "Turbo Boost" mode. The elder processor is  
the Bloomfield and the newer ones are Lynnfield. All Lynnfield i5 and  
i7 and their chipsets consume less power and have a faster (built-in)  
memory interface (DDR3-1333 instead of DDR3-1066), including also  
faster access to the built-in caches (L1, L2) then their predecessors.

> So it seems both processors have 4 real cores, and only when the  
> software is specially desgined they simulate 8 cores (and TeXShop  
> doesn't; or is it TeX itself ?). I'm not sure I am interpreting  
> things right, though.

HT (hyper-threading) is quite useful, even when you do not have  
software written for parallel execution. HT offers the system to do  
another task while this core is waiting for data to be able to  
continue the task it has started before. And because you have running  
more than 100 processes on your Mac (and almost each one is doing a  
small bit at any time) HT will give some advantage – almost for free  
(in terms of power consumption and silicon)! Safari *is* multi- 
threaded... ClamXav could check incoming eMails or downloads in  
parallel... A set of cores could deliver requested data faster to the  
MP3 player – or the TeX compiler. Faster spell(ing) correction...

> Do you think there is no point (or no obvious advantage) in buying  
> the i7 version ? I am trying to make up my mind beween the i5 and  
> the i7 versions.

300 US-$ divided by three years and the hope that TeX could become  
parallel or the compilers might learn to understand parallelisms in  
the software and produce better performing code – I'd say: YES!

When still in doubt, wait a half year! The price (for the then old  
model) will improve. But buy the new ones! Don't get fooled by 3.06  
GHz of the rancid Core 2 Duos.



Don't force it; get a larger hammer.
				– Anthony's Law of Force

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