Trying to better understand RAM frequency and latency.

1) Can anyone explain to me in a not-too-complex jargon how RAM frequency and latency affect the whole speed of the system?

2) What is the real difference between having a frequency of 1600 or 1866 or 2133 or more? How much does a gaming laptop really benefit from the increase in frequency?

3) As I understand (might be wrong though), since the numbers represent the RAM latency, is CL9 better than CL10, being a lower number? What does lower latency really do to the system?

4) What would you guys choose between these two?:
A - 32GB (4x8192) SO-DIMM DDR3 RAM 1600MHz HyperX Impact CAS9
B - 24GB (3x8192) SO-DIMM DDR3 RAM 1866MHz HyperX Impact CAS10


Sorry for the many questions, I'm trying to understand and learn as much as possible before buying.

 

1) CAS latency - Wikipedia, the free encyclopedia and memory - What does the MHz of RAM really mean? - Super User

2) There really isn't any difference, unless you plan on gaming on an integrated GPU. Otherwise, it's just a numbers game and you won't see any subjective improvement.

3) Generally, the lower the CAS number, the better. However, like RAM frequency, it doesn't have a non-trivial real-world impact, so it's just back to playing the number game.

4) What are you doing with your laptop that requires so much memory?

 

See:
Haswell And Richland Graphics Performance Scaling With DDR3


The above should be a good start for the kind of info you require.


In almost all cases, I would choose the highest capacity of RAM while keeping the modules identical in size, brand and specs.

In other words, your 'A' choice.

 

Thanks. I've been reading some articles actually and I see there isn't that much of a difference, like you say.
The laptop is meant to be primarily a gaming laptop intended to last a good 4 years at least.

 

There's isn't really a thing such as "future-proofing" in the gaming world. Unless development becomes stagnate or something.

Your biggest bottleneck isn't going to be RAM. Personally I haven't seen any games that use over 8GB of RAM, let alone anything higher. The hardware that's going to give you issues first will either be the CPU or the GPU, leaning towards GPU if you get a decent quad-core CPU. If you're not buying the RAM for capacity but instead speed, you'd be much better served with putting that money to an upgraded GPU/CPU, or even buying/installing a SSD (though you could do that after buying the laptop).

 

1) Frequency affects bandwidth, whereas latency affects access time. Higher frequency helps mainly with large sequential transfers while lower latency helps with small block transfers. If you're familiar with SSD terminology you can think of frequency as sequential transfers and latency as IOPS. Memory tends to be more sequential than disk so higher frequency helps more than latency.

In practice for most PC applications you'll hardly notice a difference. Memory is so fast compared to disk that halving either spec still means it's fast. Conversely memory is so slow compared to cache that doubling it's speed still means it's slow. Plenty of people operate with single channel memory and not even notice.

2) Bandwidth scales linearly with frequency, so 2133 is 33.33% faster than 1600. For gaming use it really only matters if you're using integrated graphics. Graphics are one application that's very bandwidth starved and you'll actually notice the improved performance from higher frequencies. If you have a discrete graphics card though then it doesn't matter since the the graphics will have it's own memory system that you can't change.

3) The CL number is timings, which is related to but distinct from latency. You can think of timings as latency represented by the number of clock cycle. Faster frequency RAM has shorter clock cycles, so a high CL high frequency DRAM could end up with less latency than a low CL low frequency DRAM. CL/Frequency*2000 gives you the latency in ns. So 1600MHz CL9 is 11.25ns and 1866 CL10 is 10.7ns.
For the most part mainstream memory since DDR days has been in the 10-15ns range, so latency hasn't really changed in the past decade. DDR4 will have similar latencies.

4) I'd pick A. Amount trumps speed trumps latency every time in my book.

 

Honestly, RAM latency/frequecy doesn't have that much of an impact on gaming (IIRC, minimum fps will be somewhat higher with faster RAM, but it won't really affect average fps).

If you really want to delve into it:
RAM latencies explained: Understanding RAM Timings | Hardware Secrets.
Everything you wanted to know about RAM, but were afraid to ask: Ars Technica: RAM Guide: Part I; DRAM and SRAM Basics - Page 2 - (7/2000) & http://archive.arstechnica.com/paedia/r/ram_guide/ram_guide.part2-1.html. This one is a bit old, but still relevant, the basics remain the same.

Not necessarily, even with superfetch and such, you start hitting diminishing returns at some point if you have no use case for that much RAM. I have 32 GB of RAM in my laptop and on a "normal office work" day, I usually have ~20 GB of free RAM that is doing absolutely nothing. Now, when I crunch numbers, it's sometimes all in use, but when I don't have a use for it, a lot of my RAM is sitting idle. Personally, I'd say that unless you have a specific need, anything over 16 GB will be overkill for most users.

 

To give one example, MOH WF causes RAM shortage all the time on a 8GB RAM switchable graphics system I used.

 

Yeah 8GB RAM isn't enough nowadays... Games like BF suck up RAM like nothing and the background processes suck up even more.. I've found 12GB to be the minimun I need and 16GB to be the max..

 

Thanks for all the replies, guys. I'm convinced now 16GB of RAM is the right amount to go for, for now. Gonna put that extra money on a better SSD instead.

 

What? I've never seen BF4 use over 2GB of RAM. The largest RAM sucking piece of software I have on my PC is by far my web browser. Google chrome seems to forget what it means to dump non-used memory. Firefox uses more RAM out the gate, but will not unnecessarily increase its RAM usage like chrome does, is my findings. I'm not denying that 8GB is not enough for a multitasker, but the games are not the problem XD.

 

I don't know about BF4, but I can say with certainty that I have seen at least one of the games I play go over 2 GB RAM. Heck, right now, with only a few things running, I'm at > 4 GB RAM. If anyone is like me and doesn't bother to close their programs, then 8 GB will become cramped fast. One of the "downsides" of having 16 GB + RAM, you stop caring about stuff running in the background as long as it doesn't take that many CPU cycles.

 

Oh I know. I hate closing stuff. But in general, most games (especially ones crying for 8GB RAM recommended) barely cross 2GB of RAM used, and even worse don't even understand what 3GB of RAM is. Not saying there aren't a few oddities out there, mind you. Just that 99.9999999% of existing ones barely crack 2GB if at all.

Of course 8GB is way too little for me and I usually use 7GB+ without even having a game running because #WhyElseBuyAPCLikeMine

 

BF4 regularly uses 2.2 GB RAM for me ... As you said, chrome eats up a lot of RAM for me so yes 8GB is just not enough ...

 

What people need to also keep in mind is that when 'testing' for how much RAM is used/allocated - that test depends on how much installed/physical RAM there is available. A system with 4GB RAM and a system with any other amount will show different % and Total RAM used even with the same workflow. Yeah, the testing bed (with regards to RAM usage) is not independent of the workflow - this is because Windows dynamically allocates RAM resources depending on the specific workload in question and the amount of physical RAM present on a platform. With more physical RAM, less instructions are paged out and more work is produced (and a more responsive system is still available even while more work is being done).

Even with todays high RAM prices (vs. circa ~2012 prices), adding RAM is just as important as adding a higher performing cpu. 'Work' can only be done in RAM by the CPU - every time it needs to touch something else (like the storage subsystem, for example), it slows the 'Work' performed exponentially.

For $200 for 16GB RAM over a 3 to 5 year period of ownership (even on an lowly $800 system), the performance increase each time the computer is used is far outweighed by the small one time cost of the RAM. Saving ~$100 and being forced to live with 8GB or less is just not a sane response to building a computer system today (and actually, for the last few years).

And the worst that could happen? Waiting until just before the end of the lifecycle of the system to increase/max out the RAM. Then, using it for less than a year and selling it for something newer anyway. To me; that is a waste of money and potential performance (over the years) thrown out the window.