# 533 vs 667 RAM bus.

## Ishiki

Given: Intel Core 2 Duo, a 5400 rpm hard drive, 1 or 2 GBs of RAM, 

will there be any noticeable, and 150$ worth, speed differences in compiling between memory of 533 vs 667 MHz ?

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## HeissFuss

I doubt you'd notice.  If you're worried about speed, upgrade your hdd to 7200RPM rather than your ram.  You'll see more improvement there.

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## Ishiki

I'm planning to buy a notebook, and I don't know if it's worth purchasing one with 667 MHz memory bus.

And I can't afford laptop with 7200 rpm HD.

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## energyman76b

yes, the difference is there.

it might be not big - but every memory access is very slow - so the faster the ram the better.

It is smarter to buy a slower cpu and faster ram, than the other way.

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## HeissFuss

 *Quote:*   

> It is smarter to buy a slower cpu and faster ram, than the other way.

 

What?  I'd like to see some benchmarks to back that statement up...

We're talking about approximately a 1% overall performance increase with 667 vs 533 ram.  Upping the CPU a notch would yield a much higher performance increase for a core2duo (5-10% for CPU intensive tasks such as compression and en/decoding.)

Your CPU spends a hell of a lot longer waiting on disk access than on RAM, which is why you'll see faster response starting programs, syncing portage or doing anything else involving files with a faster HDD.

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## energyman76b

 *HeissFuss wrote:*   

>  *Quote:*   It is smarter to buy a slower cpu and faster ram, than the other way. 
> 
> What?  I'd like to see some benchmarks to back that statement up...
> 
> We're talking about approximately a 1% overall performance increase with 667 vs 533 ram.  Upping the CPU a notch would yield a much higher performance increase for a core2duo (5-10% for CPU intensive tasks such as compression and en/decoding.)
> ...

 

a) he is talking about a laptop. For laptops 5400rpm is fast

b) you don't know what you are talking about. Every ram access costs times - hundreds of cycles. So while hdd access is definitive worse, ram is so slow compared with cpu speeds that every mhz more on the ram front is extremly usefull.

The cpu spends ages on waiting on ram every freaking second! Just think about it, where does the stuff come from the CPU is crunching? ah, from ram. And what is ridiculously slow? ah, ram....

So what do you get from a cpu that has 3,4ghz instead of 3.2ghz? Nothing in real world performance. The increase is so mediocre it does not even show up in any real world load. But with ram, even the few clocks that 667 is faster than 533 make a big difference! Becaue ram is so slow and every ram access is a horrible waste of time.

oh and just for fun:

http://en.wikipedia.org/wiki/DDR2

so in 'real' mhz, 667 is 25% faster... and in 'peak' throughput it is too....

25% that is a lot!

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## Cyker

There will be a speed difference, but not one big enough that I (personally) would spend $150 on.

It may be 25% theoretically, but in real world I heavily doubt you'll see anything near that unless you're doing something ridiculously memory intensive like CFD.

Also, I'd rather have 2GB of 533 than 1GB of 667...

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## eccerr0r

The difference between DDR2-667 and DDR2-533 will be noticed when the MHz difference of the CPU (specifically, cache) doesn't make a difference...

It all depends on your workload.  If you plan to make full use of your CPU/onchip cache, you will not notice the RAM speed difference.  If you plan to use your RAM speed (i.e., large data sets) you'd be missing cache and thus your CPU speed is no longer useful.  So whoever thinks RAM is a huge bottleneck who you pay a huge penalty...well you're right, but that's what cache is there for, and using that on-chip cache effectively diminishes the RAM speed discrepancy.

Now of course the best if you have a fast CPU and fast RAM and can run either workload... but the typical workload you'll never see the 25% speed bump at all.  I'd say a few percent tops on average, and maybe 5-10% on RAM intensive (video encoding/handling don't really count, see next paragraph; probably more like AI-type applications like chess, image recognition, annealing-synthesis, etc.; also large simulations, large photograph handling), and maybe 20% on RAM benchmarks.  I'm not sure how much work RAM benchmarks do for people though.  Shows just a number and eats electricity...

(I second the 7200 RPM HDD for the laptop and/or more RAM.  ram cache misses/demand loads have a _HUGE_ penalty, and every little bit helps here.  Video means huge files where you'll constantly be fetching from disk.)

But what am I to say, I don't know what people are doing with their computers, it's up to them to pay what they want.  If you want to overspend, I'm not stopping anyone  :Smile: 

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## HeissFuss

I asked you to show benchmarks, not the specs (obviously if it's clocked higher it'll probably respond faster, but what effects are actually noticeable?)

 *Quote:*   

> a) he is talking about a laptop. For laptops 5400rpm is fast

 

5400 is standard, even for low-end laptops nowadays.  Vendors such as Dell offer 7200rpm drives in their customizations.

 *Quote:*   

> So what do you get from a cpu that has 3,4ghz instead of 3.2ghz? Nothing in real world performance. The increase is so mediocre it does not even show up in any real world load. But with ram, even the few clocks that 667 is faster than 533 make a big difference! Becaue ram is so slow and every ram access is a horrible waste of time. 

 

Should I even bother to mention that laptops don't have CPUs at the clock rate?  These aren't P4s.

If you want some benchmarks on different CPU clock mobile systems, take a look at Tom's mobile CPU charts.

And for memory clock,

Here's a link that may actually be useful, with both synthetic and real world benchmarks for different clock and latency RAM.

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## energyman76b

Cache does not save your ass in the cold cache case. And cold cache (aka cache miss) is very common. Yes, you can mitigate some of it with bigger caches and prefetching, but at some point you are screwed. Games, videos, encoding stuff is especially screwed. Because in that cases you have to access the ram to get the new data constantly.

About benchmarks - that site used Sandra - that is almost a disqualification. Tomshardware, theinquirer and others had enough reports about sandra and its usefullness in the past. And I really doubt that anything changed.

Second run all tests except the first 'memory bandwidth' which was also a sandra benchmark, on the same cpu - not really a comparism of different speeds.

Third, if you want good benchmarks and articles about memory and the influence of it on the overall system performance, go heise.de and buy some of their magazines.

Fourth, you can test it for yourself: just downclock your ram to 166 instead of 200mhz (or whatever you have) and run your system - it is way, way slower. Why, do you think, a few years back systems with 200mhz ram (or ddr400) were trashing 166mhz (or ddr333) systems? Ah, because of ram speed. Just use google and search some articles where ddr333 board and ddr400 boards were tested - with the same cpu.

Fifth, as you can see from the link you are posted: there is a nice increase of speed with increased memory speed.

Show me one(!) workload that is not totally artifical that does not benefit from faster memory (hint, there is only one: an algorithm is spinning on a dataset that totally sits in the cache - and that needs so long to finish that the cold cache penalty on startup does not matter).

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## Akkara

 *Quote:*   

> What? I'd like to see some benchmarks to back that statement up...

 

I was recently doing some memory tuning.

Core2 Duo, 3GHz, PC6400 ram, 7200rpm seagate baracuda, playing with RAS/CAS timings and bus frequency, keeping CPU frequency constant.

The quick summary: A given x% increase in memory bandwidth as reported by memtest, resulted in approximately (x/2)% decrease in usr+sys time of compiling 2.6.22-gentoo-r2 from a make clean state using make -j3, with nothing from there cached (unmount + remount the /usr/src filesystem).

[Edit: I realized I gave the usr+sys times above.  The wall-clock elapsed time was approximately (x/3)% less, with a x% increase in memory bandwidth]

Memory bandwidth as reported by memtest seemed to be directly proportional to bus speed, when compared with same RAS/CAS timings.

So if this informal study holds in your laptop's case, the ratio of 667:533 is about 25%, I'd expect to see 8% speed improvement in elapsed time in compilation type jobs, and up to 12% in compute-bound jobs.  I'd say, yea, get the better RAM.

An interesting followup comparison would be to time building the kernel in ramdisk versus on hard disk to get an idea how much effect drive speed has.  I can be persuaded to do that later if there's interest  :Smile: 

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## Ishiki

I would like to thank You all for participation in the discussion.

I've ralised long time ago that there is, of course, a way to have not only 667 MHz RAM, but even a 7200 hard drive - a barebone.

But I am not sure if it's ok to risk, as barebones can have keyboards and matrices/screens/displays of a lesser quality.

Maybe I could find a store nearby that has some VBIs in stock, so I could touch and see them...

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## Akkara

I just noticed you're also considering 1 or 2 GB.

I'd go with 2GB, if you can afford it.  More memory = bigger disk cache = speed of the disk isn't as important.

If I were to guess, I'd rank your choices like this, in order from worst to best:

1GB @ 533, 5400 rpm

1GB @ 667, 5400 rpm

2GB @ 533, 5400 rpm

2GB @ 667, 5400 rpm

2GB @ 667, 7200 rpm

And in fact I'm not so sure about the last one even if affordable.  Faster disks also take more power and make more noise which is a mixed tradeoff in a laptop.

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## Ishiki

 *Akkara wrote:*   

> More memory = bigger disk cache = speed of the disk isn't as important. 

  I uderstand, but before something gets into the cache, it has to be read from disk. Apps that are started for the first time after booting the system, reading and writing files in compilation process - in these, HD's speed really matters.

When something is in the RAM already (a portion of code that is being compiled atm.), HD's speed has no effect.

The best buy would be a barebone notebook with 1 / 2 GB of 667 MHz RAM and a fast, 7200 rpms hard drive.

But there are always some buts  :Very Happy: 

Barebones may have displays a class or two worse than 'normal' notebooks and maybe there is greater possibility that a dead pixel will appear.

I will have to read some more about it...

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