(DDR4 RAM) what does the CAS numbers mean?

[Jackb57]

I was looking further into what ram to choose and was having problems understanding why certain ones of the same size and speed had price discrepancies of around £50? the only difference i could see were between a few numbers?

For example this has 'CAS 14-16-16-31' (http://www.scan.co.uk/products/32gb-%284x8gb%29-corsair...)

and this has 'CAS 13-15-15-28'? (http://www.scan.co.uk/products/32gb-%284x8gb%29-corsair...)

Is there any form of performance difference between these two or is it literally just a different price?

 

[Jackb57]

AND could anyone give me an estimate on whether the performance boost between 2133 MHZ DDR4 and 3000+MHZ would be noticeable in the real world?

 

[BadBoyGreek]

Without getting too much into the science behind CAS latency, it's basically the time between when a memory controller sends an instruction to the memory to retrieve information and when it actually reaches the RAMs pins. Lower numbers refer to faster retrieval times. Will you notice a significant difference in the performance? It depends on how much variation there is in the numbers, but overall, unless you're consistently running your system at peak load operations, the real-world difference is relatively negligible.

You can read more about CAS latency here:

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

As for your second question, any RAM speed beyond your CPU's rated speed is strictly for overclocking purposes. If you're running your RAM at the CPU's default speed, then having DDR 3000+ or whatever won't result in increased speeds unless you overclock your processor. That being said, how noticeable a performance increase you get with higher RAM speed / settings depends on just how far you're able to push your speeds, but stability should always be the primary objective when overclocking.

When we're talking about "real world" performance, it depends on your day to day tasks. Would you notice the speed difference when launching your e-mail app, MS Word or whatever? No. Would you notice it when doing photo / video rendering and encoding? Yes. It all depends on what you're doing.

Hope some of that was helpful

 

[Jackb57]

"Real world" was a bit vague sorry, and thanks for the info.

Its for Photoshop graphic design/photo editing.

The reason i am confused is that there is 300% price increase in what would seem to the average person the same.
I want to make sure I do not spend to much on something that won't matter, and at the same time, not being a skint flint on somethign that would matter to us.

I have posted about our build here:
http://www.tomshardware.co.uk/answers/id-2574690/photoshop-build-batching-1000-images.html

Bu thought I'd quiz ram also separate.

Maybe I am going 2 deep? but we plan on keeping this for a long time so rather get it nailed correctly, and gone so far with exploring options, I think its knowing when to quit reading and just buy.

That day will be tomorrow ! (he says )
32GB (4x8GB) Corsair DDR4 Vengeance LPX Black PC4-19200 (2400), Non-ECC Unbuffered, CAS 14-16-16-31, XMP 2.0, 1.2V 32GB £266.65 2400 14
32GB (4x8GB) Corsair DDR4 Vengeance LPX Black PC4-17000 (2133), Non-ECC Unbuffered, CAS 13-15-15-28, XMP 2.0, 1.2V 32GB £299.32 2133 13
32GB (4x8GB) Corsair DDR4 Vengeance LPX Black PC4-21300 (2666), Non-ECC Unbuffered, CAS 15-17-17-35, XMP 2.0, 1.2V 32GB £359.32 2666 15
32GB (4x8GB) Corsair DDR4 Vengeance LPX Red PC4-21300 (2666), Non-ECC Unbuffered, CAS 14-16-16-31, XMP 2.0, 1.2V 32GB £379.32 2666 14
32GB (4x8GB) Corsair DDR4 Vengeance LPX Black PC4-22400 (2800), Non-ECC Unbuffered, CAS 16-18-18-36, XMP 2.0, 1.2V 32GB £539.32 2800 16
32GB (4x8GB) Corsair DDR4 Dominator Platinum Kit, PC4-22400 (2800), Non-ECC Unbuffered, CAS 16-18-18-36, XMP 2.0, DHX 32GB £639.32 2800 16
32GB (4x8GB) Corsair DDR4 Dominator Platinum Kit, PC4-24000 (3000), Non-ECC Unbuffered, CAS 15-17-17-35, XMP 2.0, DHX 32GB £729.32 3000 15

 

[BadBoyGreek]

If you plan to keep the system for a while and you want to get the most out of it long term, investing the extra bit into the lower latency RAM may be worth the additional investment, though I believe Photoshop rendering performance is more driven by raw CPU power than RAM latency. Frankly, I think you would be hard pressed to tell much difference between the two either way, maybe seconds or a minute or two on a really long render, if that.

As for faster RAM, don't bother unless you're going to overclock at some point. If you're sticking with stock clocks, get a good set of RAM that matches the speed of the processor's bus. The faster speed ratings on the RAM don't mean it will run at that speed, it just means that the RAM itself has greater headroom for those who want to overclock. By default, RAM will run at the speed of the CPU's bus speed, regardless of how fast the RAM is rated for.

 

[Jackb57]

Thanks again for the info. Its good to fully learn and understand about how the machine will work, I am interested in all this as much as the photoshop work.

So I have learnt from you that if going for this cpu...

Intel Core i7-5820K 3.3GHz 6-Core Processor

For photoshop with 32 GB ram, money no object then this ram..

32GB (4x8GB) Corsair DDR4 Vengeance LPX Black PC4-17000 (2133), Non-ECC Unbuffered, CAS 13-15-15-28, XMP 2.0, 1.2V 32GB £299.32 2133 13

Is the ram of choice, and with this setup and use will perform as good as any ram that costs more?

Is this correct? If so, final question....

What boast is possible to this system for a extra £500 (50% EXTRA) and for what potential performance percent increase?

PC PARTS LIST
http://uk.pcpartpicker.com/p/H7r7Hx

Cheers

 

[BadBoyGreek]

Thanks again for the info. Its good to fully learn and understand about how the machine will work, I am interested in all this as much as the photoshop work.

So I have learnt from you that if going for this cpu...

Intel Core i7-5820K 3.3GHz 6-Core Processor

For photoshop with 32 GB ram, money no object then this ram..

32GB (4x8GB) Corsair DDR4 Vengeance LPX Black PC4-17000 (2133), Non-ECC Unbuffered, CAS 13-15-15-28, XMP 2.0, 1.2V 32GB £299.32 2133 13

Is the ram of choice, and with this setup and use will perform as good as any ram that costs more?

Is this correct? If so, final question....

What boast is possible to this system for a extra £500 (50% EXTRA) and for what potential performance percent increase?

PC PARTS LIST
http://uk.pcpartpicker.com/p/H7r7Hx

Cheers

Sorry for the delayed reply. That RAM is definitely what you want to go with based on the CAS latency numbers.

Looking at the rest of your parts list, you've got a pretty substantial build there and aside from a higher end CPU, the room for improvement is limited. You could go with an M2 form factor drive instead of the Samsung, which would provide better IO performance. You could also choose to get a second Samsung drive and use RAID 0 which will also give you enhanced IO performance. If you really want to go all out, you could go for the i7 5960x CPU and get the additional 2 cores which would be most beneficial to your Photoshop and other multi-threaded app needs.

As to what percentage increase in performance you can expect, it's difficult to quantify as performance will vary depending on your application. Going with the 5960x, on paper would, theoretically give you at least a 33% performance boost by virtue of 33% more cores, but this also depends on how well optimized your apps are to take advantage of multi-threading, which Photoshop is for example. Based on the list though, I'd say your biggest improvements will either come from the M2 drive, RAID 0 SSDs or the higher-end CPU.