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CPU Cache - Everyones Favourite

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December 12, 2012 7:41:15 PM

Hello,

I am considering upgrading my PC MB & CPU but I am confused about the Cache Memory.

I think I understand what it does, my understanding is that cache memory is instant memory within the CPU (L1, L2, L3) that the computer can retrieve quickly as opposed to slowly from the RAM modules (L4, L5)

My question, what CPU out of the 2 below has more efficient Cache memory?

AMD's offering (the amd-fx-4100) with a total Cache of 12mb split 4mb in L2 & 8 in L3

see here http://www.dabs.com/products/amd-fx-4100-am3--3-6ghz-12...

OR

Intels offering (the Intel® Core™ i7-920 Processor) with a total Cache of 8mb which I assume is L1 Cache

see here http://ark.intel.com/products/37147/Intel-Core-i7-920-P...


now the price difference between these two processors is a dead giveaway :o  but I am trying to identify what is value for money in terms of efficiency. i.e. does 4mb of L1 Cache memory have the same efficiency of 12mb split 4mb in L2 & 8 in L3?

Any help would be greatly appreciated
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December 12, 2012 8:41:19 PM

There is major differences in cache. L1 is never high enough to be 8MB. Usually around 1, L2 is about 4-6, and L3 is 6-12. L1, L2, and L3 caches are also used for different instruction sets - the more you have for each one, the better. Go with the i7 because the cache plus CPU performance will top the FX.
While cache is important, so is cores. The FX uses 2 real cores but they are seen everywhere as 4. Pseudo cores. Not the same as 4 individual, raw cores.
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a b } Memory
December 12, 2012 8:59:10 PM

With the same price of a good quality motherboard for the i7 920, you should be able to get a Sandy Bridge processor and motherboard. The 1366 platform is very expensive and it is out of date.

Tell us your budget and what the PC is for, then we should be able to help you.
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December 12, 2012 9:02:28 PM

i agree with payturr, and wanted to add: if you want to go with intel, get a current gen (ivy bridge) CPU and motherboard. The i7 920 came out in 2008, as you can see on the website. Intel has a tendency NOT to lower the price on older parts.

I advise to get a i5-3570K or a i7-3770K. They are about the same in performance/core, but the latter supports hyperthreading for a total of 8 logical cores. This is only important if you do great amounts of video editing, scientific calculations and the like. But that feature sets you back another ~100$ compared to the i5, your call if you think it's worth it.
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December 12, 2012 9:27:05 PM

+1 to Ivy Bridge. And don't worry too much about the specs - they're a means to an ends. Why not look at the benchmarks and just see the end result? It's kind of like speculating on a car's 0-60 time based on the horsepower. Why bother guessing when there's a published 0-60 figure that gives you the true performance?

If you've found some deal on the i7 920 by the way, it's an excellent processor and will game every bit as well as the newer Intel ranges (there's been very little progress since Nehalem for gaming performance), however it will consume a fair bit more power. You're looking at 130 watts TDP vs 77 watts on the newer CPUs. I used to think it was a weak argument (it's often used against AMD's current CPUs) but then I did the math on it, and the annual costs really do add up, especially when you factor in PSU efficiency (which will exacerbate these power consumption differences).
December 12, 2012 10:29:04 PM

Hey guys thanks for the feedback i want to upgrade for Gaming (total war series), Autodesk, basic Photoshop & 2 monitors, my budget was around £200 At the moment my current PC has an
AMD Athlon 2x4 640,
BIOSTAR A780L3L with
4GB DDR3,

any suggestions to avoid a complete overhaul?

The reason I am considering a complete overhaul is, I bought a basic graphics card (Radeon HD 5450) and it won’t register on the PCIe strip on the MB, I have tried everything including the BIOs settings and I am beginning to think it is the MB.
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December 12, 2012 11:55:41 PM

This system has a good basic specification if you are not planning on overclocking and just want to add a a video card:
http://www.mwave.com.au/product/sku-ab47713-mwave_essen...
- It is rather overpriced though, I am sure you can find the parts much closer to $425.

================================================================

CPU's have L2/L3 cache due to economics.
- Having 4GB to 8GB of SRAM would cost an absolute fortune and use heaps of power.
- So a cache used with a hit rate of >= 70% using much less resources and we use DRAM (eg: DDR3-SDRAM) for memory as it is much cheaper to produce and uses much less power than SRAM.

AMD's caches are usually exclusive so each level adds to the next.
Intel's caches are usually inclusive so each level mirrors the data in the level above it, plus some.

Intel's caches usually have higher x-way set associativity which yields greater performance in gaming workloads using less storage. (Basically they can keep the cache hit ratio high enough without using stupidly large caches).

Thanks to memory increasing in performance so much due to various factors, integrated memory controllers and the like, we don't require 128MB Lx caches in todays systems.

Larger caches are better in server workloads when there is a lot of virtualization/consolidation going on. Especially if each CPU in a sytem can snoop the other CPU's caches via a high performance transport via a ccNUMA type set-up.

AnandTech have a dated article that explains it more:
- http://www.anandtech.com/show/1066/5
a b à CPUs
December 13, 2012 11:02:19 AM

LOL Scott... how do you know all this stuff? You're like a tech encyclopaedia! You write assembly code for a living?
a b à CPUs
December 13, 2012 11:51:35 AM

No idea what you're talking about (hehehe):

a b à CPUs
December 13, 2012 11:58:02 AM

Haha damned emoticons :-) So you are a programmer? I think I saw your blog (can't remember where I saw the link) and it looked like you do web development work?
December 13, 2012 12:07:17 PM

sam_p_lay said:
+1 to Ivy Bridge. And don't worry too much about the specs - they're a means to an ends. Why not look at the benchmarks and just see the end result? It's kind of like speculating on a car's 0-60 time based on the horsepower. Why bother guessing when there's a published 0-60 figure that gives you the true performance?

If you've found some deal on the i7 920 by the way, it's an excellent processor and will game every bit as well as the newer Intel ranges (there's been very little progress since Nehalem for gaming performance), however it will consume a fair bit more power. You're looking at 130 watts TDP vs 77 watts on the newer CPUs. I used to think it was a weak argument (it's often used against AMD's current CPUs) but then I did the math on it, and the annual costs really do add up, especially when you factor in PSU efficiency (which will exacerbate these power consumption differences).


Hi sam_p_lay, Just wanted to ask is there a performance benchmark website that I can look at?
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December 13, 2012 5:26:24 PM

martmart said:
Hi sam_p_lay, Just wanted to ask is there a performance benchmark website that I can look at?


You're looking at it :-) A lot of people don't seem to realise Tom's Hardware isn't just a forum - it's a tech media site with a forum stuck on it! Second item on the menu up there ^ or just check out http://www.tomshardware.co.uk/review/Components,1/CPU,1...
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December 13, 2012 5:29:00 PM

This article in particular tests a good range of CPUs - http://www.tomshardware.co.uk/fx-8350-vishera-review,re...

That links you to the first page of benchmarks, plenty more to navigate through after that. The gaming benchmarks are a bit later in the article. You'll find loads of articles/reviews there though with benchmarking.
!