[SOLVED] A few questions about RAM

[MattMax]

I've always thought that pretty much the only thing you have to keep in mind when choosing RAM is to make sure its frequency is supported by the motherboard, and that's what I did.

My motherboard and RAM both support 1600 MHz, but according to CPU-Z, the actual frequency is 1333 MHz instead (or ~669 MHz x 2 to be exact). I've been trying to figure out why, and managed to find two possible reasons.

Reason #1: The frequency was set by the manufacturer to a "safe" value, but can be increased at any time to the advertised value. This doesn't really make sense to me. If RAM is supposed to run at 1600 MHz, and the motherboard supports that frequency, why doesn't it do that from the get-go? It seems like there's a risk involved in increasing the frequency to what it's supposed to be, which is strange (we're not talking about overclocking after all).

Reason #2: The reason why the frequency is lower is because that's as much as the CPU can handle. This makes a lot more sense to me. Until recently, I had no idea that CPUs (similarly to motherboards) have a maximum RAM frequency that they can support. The PC I use is old and its CPU supports only 1333 MHz DDR3 RAM. I'm pretty sure it's the bottleneck that limits the frequency, but I'd like to hear it from you guys. Btw. What if I enter BIOS and set the RAM frequency to 1600 MHz? Will it get changed back to 1333 MHz because of the CPU? And what if I overclock the CPU? Will it increase the maximum supported RAM frequency it supports too?

I've got two more random questions about RAM if you don't mind answering them:

1. Can I use two different kits of two memory modules (i.e. 2 identical Kingston modules, and two identical Corsair modules) in dual channel as long as I put modules from the same kit in the same channel? The final setup would look like this: channel 1 = 2x Kingston, channel 2 = 2x Corsair. Same size, frequency, and CL. (Btw. What if let's say the CL is different? Does it completely break dual channel?)

2. Why do games usually need a lot of RAM? As far as I know, textures are the largest files and they go to VRAM (unless there's no more room in it). So what exactly requires gigabytes of RAM as far as games are concerned?

Thank you for your time!

 

[Darkbreeze]

Memory has default profiles, which for DDR3 is generally 1333mhz, and for DDR4 is 2133mhz. That is what ALL memory modules will generally default TO unless you set or enable the XMP profile, for memory kits that are faster than what can be defaulted to. Some motherboards might default to something higher than those if the CPU supports it, but if it sees any issues with the configuration (And sometimes just to play things safe, even if it doesn't), it will simply default to a very loose set of timings and a baseline frequency (Speed) in order to err on the side of compatibility as outlined by the default JEDEC profile programmed onto the module.


Anything beyond the most basic profile speed and configuration depends on the sticks, the motherboard and the CPU, as a package, as to what will happen. Nothing is ever just "supposed" to run at higher frequencies. Almost always, anything beyond the default frequency needs to be configured by the user. Obviously, there are SOME exceptions to this, for example many of the 9th gen Intel platforms will default to 2666mhz, but if you use 3200mhz sticks in that same platform it's not just going to run at that speed out of the box. You WILL need to set the XMP profile.

Furthermore, it is ALWAYS a good idea to set the XMP profile when possible, BECAUSE the timings that are a part of that profile might be moderately tighter (better) than the timings that are used by the fail safe default JEDEC profile.

Technically, the fact that "that is all the CPU can handle" is a misnomer. It is a factor, but not in the way that most people think.

When you go to the specifications page for an Intel processor, for example, and see that it says 2666mhz, that does NOT mean that that is the highest speed that CPU can support. It ONLY means that that is the highest speed that that CPU can support by DEFAULT. And it doesn't mean that that is what the motherboard WILL default to, only that the platform is ABLE to do so if the motherboard and CPU are in agreement that it's a stable configuration. If the motherboard doesn't like something, it will default to the baseline configuration for that memory platform.