Don't Fill Memory Slots?
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Posted by gecko on June 28, 2008, 7:29 am
Please log in for more thread options performance you should avoid filling all of them. Usually filling of just two slots is best." It doesn't meet the test of reason. In order for this statement to be true, the system would have to deduct more than the value of the fourth piece. This says two 512s will yield 1 G, but four 256s won't. That they might actually yield less than 768MB. Ever hear of this? Thanks -GECKO | |||||||||||||||||||
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Posted by Big_Al on June 28, 2008, 8:12 am
Please log in for more thread options I wonder if they are referring to putting in 4 x 1gig chips. XP 32bit only addresses max 4 gigs and the hardware consumes some of the 4 gig space thus you only get like 3.2 to 3.5 gig of usable memory. Thus putting in 3 chips is almost as good as putting in 4 chips. I'm over simplifying this, but you get the basic idea. There have been lots of writeups about this in hardware NG's. | |||||||||||||||||||
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Posted by John McGaw on June 28, 2008, 8:40 am
Please log in for more thread options gecko wrote:
> PC Mag tip: ". . . if your PC has four memory slots, for best
> performance you should avoid filling all of them. Usually filling of > just two slots is best." > It doesn't meet the test of reason. In order for this statement to be > true, the system would have to deduct more than the value of the > fourth piece. This says two 512s will yield 1 G, but four 256s won't. > That they might actually yield less than 768MB. > > Ever hear of this? > > Thanks > -GECKO I can think of interpretations but without seeing the original "tip" I won't venture a final reply. How about a link so we can see exactly what it is they wrote? One idea that comes to mind is that some chipsets don't handle the extra loading of more sticks gracefully. In other words, they can use more aggressive memory timing with two sticks than they can with four sticks. -- John McGaw [Knoxville, TN, USA] http://johnmcgaw.com | |||||||||||||||||||
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Posted by Paul on June 28, 2008, 10:46 am
Please log in for more thread options John McGaw wrote:
> gecko wrote:
>> PC Mag tip: ". . . if your PC has four memory slots, for best
>> performance you should avoid filling all of them. Usually filling of >> just two slots is best." >> It doesn't meet the test of reason. In order for this statement to be >> true, the system would have to deduct more than the value of the >> fourth piece. This says two 512s will yield 1 G, but four 256s won't. >> That they might actually yield less than 768MB. >> >> Ever hear of this? >> Thanks >> -GECKO >
> I can think of interpretations but without seeing the original "tip" I > won't venture a final reply. How about a link so we can see exactly what > it is they wrote? > > One idea that comes to mind is that some chipsets don't handle the extra > loading of more sticks gracefully. In other words, they can use more > aggressive memory timing with two sticks than they can with four sticks. > I think that is what they're getting at. If you had an Athlon64 with four DDR memory slots, you could run two sticks at DDR400 Command Rate 1T. If you install four sticks, then DDR400 2T or DDR333 1T would likely be speed/timing settings for the RAM. The lost in memory bandwidth is about 20%, by going to 4 sticks on Athlon64, with an application performance loss of around 6%. (This assumes the sticks are double sided, and the biggest capacity sticks will be that way.) On a modern DDR2 motherboard, I feel you have less to worry about. At one time, Anandtech used to include 2 stick versus 4 stick test results, and on DDR2, there was hardly any change to the CAS and other settings. So for DDR2, the performance loss is not a guarantee. Perhaps if you were operating at extremely high DDR2 clock settings, there would be enough of a loading effect to care (so it you were trying to take top spot in the Futuremark ORB, you might dispense with four sticks and try two). Naturally, there are exceptions to every observation. There are some boards, where if you read the reviews, you can see they're not that good when it comes to the memory bus design. They seem to be unstable with four sticks. But that doesn't mean it is the fault of the technology, but rather a badly designed instance of motherboard or chipset. Which is why you should read the reviews, before buying that motherboard to take four sticks. In terms of getting memory capacity stated, you always get the capacity in bytes. If you install 4 * 256MB, then there will be 1GB of storage locations present in the computer. But if the BIOS is planning an address map for all the hardware (which routes certain addresses to certain hardware resources on the board), then you could find in that case, that some memory is "unreachable". If a system was limited, for whatever reason (*), to a 4GB address space, you have 4GB of memory installed, two 512MB video cards, then *something* in the box is not addressable. The BIOS chooses to not completely map the memory in that case, so only the bottom section of the memory is available for use. The top part of the memory is still there, but no bus operation of the processor can read it or write to it. In that case, the memory reported in Windows, has to be less than 4GB, since Windows will not be able to access the upper part of memory. With the low price of memory, for most people, that loss is a "don't care". For those worried about getting their "money's worth", they could always try a 2x1GB + 2x512MB config of DDR2 sticks, for a total of 3GB. (*) To make the previous paragraph shorter to write, I didn't go into details of the limitations caused by a 32 bit OS, versus a 64 bit OS, versus chipsets that support memory remapping and ones that don't. And so far, I haven't seen a single web page, that does a good job of addressing the issues thoroughly. Paul | |||||||||||||||||||
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Posted by VanguardLH on June 28, 2008, 5:24 pm
Please log in for more thread options
> PC Mag tip: ". . . if your PC has four memory slots, for best
> performance you should avoid filling all of them. Usually filling of > just two slots is best." > It doesn't meet the test of reason. In order for this statement to be > true, the system would have to deduct more than the value of the > fourth piece. This says two 512s will yield 1 G, but four 256s won't. > That they might actually yield less than 768MB. > > Ever hear of this? > > Thanks > -GECKO Yes, I've heard of this. It all depends on the capacity of the memory modules you insert. The more capacity, the more current get consumed. There may be a maximum current draw across all the slots that you must not exceed. 4 256MB sticks in 4 slots will draw less current than 4 1MB sticks in those 4 slots. The mobo may even say that it supports 2GB memory modules but you cannot put more than 2 in because those 2 already draw the max current and 4 2GB sticks in 4 slots would be beyond the milliamps that the mobo can supply to all 4 slots. There is also the issue that you might use memory modules that exceed the addressing bus width for the memory slots. You will have to stay under the max capacity per memory module that the mobo specifies (while also staying under the max current draw). However, exceeding the max addressing width applies to all slots. The only reason why I mention this is because users often replace with higher capacity modules which can then exceed the address bus width. The result is that they won't get the full capacity of the memory modules. It might also refer to dual channel mode which requires memory modules in pairs. If you add 2 memory sticks (and in the correct slots) then dual-channel mode is enabled. If you add 1 memory stick, you obviously can't do dual-anything. If you add 3 memory sticks, you may or may not get dual-channel mode. For some mobos, the first 2 sticks (in the paired slots) will be dual-channeled while the 3rd stick is not. In some mobos, you lose dual-channel model altogether. So is this "tip" somewhere online so the rest of us can read what you read to know what it really said? | |||||||||||||||||||
> performance you should avoid filling all of them. Usually filling of
> just two slots is best."
> It doesn't meet the test of reason. In order for this statement to be
> true, the system would have to deduct more than the value of the
> fourth piece. This says two 512s will yield 1 G, but four 256s won't.
> That they might actually yield less than 768MB.
>
> Ever hear of this?
>
> Thanks
> -GECKO