A friend of mine told me that your typical motherboard nowadays has a RAM controller that will only accommodate RAM in multiples of 3GB, so it really doesn’t make sense to buy 8GB of RAM on your typical computer today because the motherboard will only see 6GB anyway.
This is not word-for-word, so don’t knock my friend if it doesn’t make sense.
I have three questions, since I don’t have extensive computer knowledge:
What is a RAM controller anyway?
Is the first paragraph accurate? If so, why would RAM controllers be designed in such a seemingly inefficient way?
If the answer to 2 is “no”, is there some kernel of truth in the first paragraph? Could my friend have been trying to say something else that I just didn’t quite understand or that he didn’t quite know everything about?
Different motherboards sometimes have different requirements for the RAM they will accept (e.g. in pairs or all the same size and such) but generally they will take what you give them.
The only thing I can think he might mean is that a 32-bit operating system (most installs of Windows are 32-bit although 64-bit is definitely out there) can only take a max of 4GB. You could put in 8GB but it will only see 4GB.
Thing is the 4GB is ALL the memory in your system so things like the RAM on the video card count towards the total. Considering that many decent video cards now have near a gig of RAM themselves there is no point to buying more than 3GB for your system.
If you want to have more than 4GB of RAM you need to get a 64-bit OS.
No expert but what I’ve picked up in recent research.
Intel’s newest quad core CPUs(some of the i7 series) have triple channel RAM slots on the motherboard resulting in RAM in multiples of 3. The i5 and lower end i7 CPUs use a dual channel slots thus using ram in multiples of 2.
Hopefully, some of our experts will be by to explain more clearly.
I’ll go for some simple answers first. I’m sure others can supply more complex answers.
RAM controler: essentially the part of the computer that accesses the memory.
No. RAM is usually sold in powers of 2 and multiples thereof.
I’d guess that he was trying to say that the new Core i7 processors from Intel support a triple channel mode. This means that, if you have 3 sticks of identical memory, you can make the memory work faster than if you don’t. It’s difficult to divide 8GB into groups of three, so triple-channel mode would not be available.
Whether the difference is high enough that 6GB is better than 8GB, I don’t know.
ETA: And in going to find links to help you, some of my info was already given.
This is true. But even then, it’s more of a case of optimal performance. You can put any number of RAM modules you want in, but you get the best memory bandwidth if you put in matched sets of 3. This gives you a modest performance benefit; some applications benefit significantly, others not so much. It probably wouldn’t be noticed for most ordinary users, using just office and their web browser.
Up until the previous generation of Intel x86 CPUs, and somewhat earlier for AMD ones, memory was hooked up to the Northbridge component of the supporting chipset. Newer CPUs address memory directly. With this change, sometimes a CPU is configured to have an odd number of memory channels. For example, the Intel “Bloomfield” chips have 3 memory channels. However, that just controls how the CPU routes data to the memory modules - you could still install memory in many combinations that would provide 8GB usable from 8GB installed memory. As a specific example, the Supermicro X8SAX/C7X58 motherboard routes those 3 channels to 6 sockets, and you could install any number memory modules (1 through 6).
Memory controllers are usually designed to support power-of-2 increments of main memory. There are some restrictions, such as a system that only supports 4GB being limited to less due to the need to leave “holes” for expansion cards and other things. Even with a 64-bit operating system, some computers w/ 4GB installed will show only 3GB - the chipset can’t address memory past the 4GB line, so it gets clipped to 3GB. The Dell Dimension 8400 is one such system.
Is it possible that your friend was referring to cache memory? That resides on the CPU chip in recent systems, and there are occasionally “odd” sizes there - for example, a CPU with a 1MB primary cache and a 2MB secondary cache could be said to have 3MB of cache. A dual core with independent caches could thus report 6MB.
I’m typing this on a system (Dell Optiplex 755) that uses an Intel Q9650 CPU, which reports 12MB of cache memory (actually 4 * 32KB + 4 * 32KB + 2 * 6MB). The system itself has 8GB of RAM installed (4 2GB modules) and Windows reports “8.00GB (7.87GB usable)”.
One limitation is that some memory controllers want memory to be installed in pairs. The Dell Dimension 8400 I mentioned earlier is one of those. So, since it can’t address more than 3GB of RAM, I have 2 * 1GB + 2 *512MB modules installed. It would work equally well with 4 * 1GB modules, though it would still only show 3GB usable.
I don’t agree that the RAM on a video card installed in a PCI/AGP/PCIe slot is controlled by the mother board CPU. Instead it it controlled by the GPU on the video card. Many of these boards contain RAM which is not compatible with the main board (for instance DDR3 where the main board only allows DDR2).
If the video board is part of the mother board, of course, it shares the main RAM.
Correct. It is more appropriate to think of the video board as a coprocessor with its own private memory, some of which is shared with the main CPU. Applications like Folding@home take advantage of this to gain huge speed improvements using the multiple cores of modern graphics CPUs.
This depends on what graphics chipset is in use. Some are pretty much complete video boards with private memory that happen to be part of the mainboard. High-end notebook PCs are usually of this type.
Some video controllers can optionally use main system memory, and some others require the use of main memory as they have no private video memory. In these cases, the memory is sometimes “stolen” from the main system memory by magic in the chipset - memory assigned in this way doesn’t show up as main memory once it has been remapped.
I wouldnt sweat it. Real world testing of dual channel RAM doesnt result in 50 or 100% gains in RAM performance but more around 5-10%. If you have an odd (or even in your case) number of RAM modules, you’ll be fine. You probably wouldnt notice the difference anyway. Your system will see all the RAM.
Not sure if you are referring to my post but if so it is missing the point.
Video cards (and other stuff) count towards your RAM limit on a 32-bit OS. Put in 4GB and a video card with a lot of memory and check the System Information. It will not report 4GB.
I have a machine running Windows 7 with 8 gigs of RAM, and it doesn’t start to run slow until I’ve put more than 7 gigs worth of data in memory, not including overhead and OS stuff. And you can bet that if it was really 9 gigs they’d market it as 9 gigs
Most Intel i7 (as mentioned by BigT) systems are sold utilizing Triple-Channel Memory architecture, with 3, 6 or 12Gb (no 9Gb). AMD CPUs and Intel i3/i5 CPUs are Dual-Channel systems.
In an interleaved memory system, consecutive memory addresses are read from different memory sticks, so that one chip can be transferring data to the CPU while the next read is prepared on another stick. This improves throughput. For many years, interleaved systems have been dual-channel, making the design simple - odd memory addresses are retrieved from one stick, even from another. Triple-Channel designs are more complex, and have only recently been implemented. This co-ordination is managed by the RAM controller (usually part of the NorthBridge). The better the integration between CPU and RAM controller, the faster the CPU can access memory.
This isn’t true. Using physical address extension a 32-bit processor can access up to 64 GB of RAM. I don’t know about 32-bit versions of Windows, but 32-bit Linux has long made use of this feature.
My motherboard is rather picky with memory. It needs as a minimum 2 memory sticks (it won’t start at all with just one). Also depending on the number of sticks, there are specific slots where they have to be inserted, else it won’t recognize some of it.
I’m guessing he is trying to suggest that the best strategy for a motherboard using triple channel memory is to use RAM DDR3 chips in triplets instead of pairs.
Many motherboards have 4 slots for RAM chips. There is an optimum configuration for any motherboard based more on the motherboard design than any other factor. Say Slot 1 and 2 have their own channel and slots 3 and 4 share the third channel. For the absolute best performance, you want to balance the memory across the channels. For an 8 Gig set up you’d have 3/3/2/2; the use of the 4th slot would slightly decrease maximum memory bandwidth although this would be more than compensated for in overall performance by the added total amount of RAM. In a 9 GB config you’d have 3/3/3 and the 4th (shared channel) empty. Using a 3 GB DDR3DIMM in the 3rd slot gives you better efficiency plus more total memory, and I’m guessing this is where he got that particular number from.
I believe the memory controller in i7-based systems is integrated into the chip and not on a separate (northbridge, e.g.) controller, and I believe the chip can switch from single to triple to dual channel depending on how the memory is set up, but this is way over my head. I suspect the average user is not likely to notice much difference from one mode to the other, triple channel being more of a theoretical than practical advantage.
It does make a difference, I think, to fill the mobo memory slots in the order in which the mobo manufacturer suggests.
It is NOT correct that the motherboard will only see 6 GB in a 3/3/2/2 setup, btw. It will see all 8 GB as long as the correct DDR3 DIMMS are used.
Correction to my post above:
Since memory typically comes in 1,2 and 4 GB (not 3 GB/DIMM), my examples are wrong but the concept is right.
8 GB would be 2/2/2/2 and 9 GB would be 4/4/0/1 (or whatever, depending on the mobo recommendation of which slot to use) for 4 slot mobos.
On a newer motherboard with 6 slots, memory would be ideally set up in triplets, say 2/1/2/1/2/1 for 9 GB; if only 8 GB are installed I don’t think you’d get true triple channel performance but you would still see all 8 GB.
As support for what everyone else seems to be saying I’ll just quietly mention that the PC on which I’m typing this seems to see all of the 8GB of RAM that’s installed on it. According to the “computer / properties” window it’s an HP e9230f with an Intel® Core™2 Quad CPU running under Windows 7 Professional.
