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Installing DIMMs, order of slots
There seems to be a common wisdom that one should always populate DIMM slots
starting with the lowest-numbered slot. However, I've never seen an explanation as to why this is. I have reason to believe that my second slot may be faulty, but I'm not sure if Memtest will be affected by the fact that in order to isolate the issue, I can't have a DIMM running in the first slot. Actually, I do know that Memtest reports the speed of the chip differently depending on whether I put it in the first slot or the second slot. Then again, I am using an AMD processor with an integrated MC, so maybe it is also something to do with the CPU. Anyone have answers? |
#2
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Installing DIMMs, order of slots
cyg wrote:
There seems to be a common wisdom that one should always populate DIMM slots starting with the lowest-numbered slot. However, I've never seen an explanation as to why this is. I have reason to believe that my second slot may be faulty, but I'm not sure if Memtest will be affected by the fact that in order to isolate the issue, I can't have a DIMM running in the first slot. Actually, I do know that Memtest reports the speed of the chip differently depending on whether I put it in the first slot or the second slot. Then again, I am using an AMD processor with an integrated MC, so maybe it is also something to do with the CPU. Anyone have answers? In digital design, things have "signal integrity" issues. Any time there is a shared bus concept, there is a possibility that some hardware configurations give better signal quality than others. And that can affect the speeds used by the BIOS. On DDR memory, there are terminator resistors to help absorb reflections at the end of the bus. With those in place, the slot position should be less sensitive. (In this picture, Rt is a terminator at the end of the bus lines. This picture does not show the RAM slots, and they would be located where that coaxial symbol "bus" is located. This bus termination scheme is called SSTL.) http://media.maxim-ic.com/images/app.../1775Fig01.gif In the Northbridge (integrated or discrete), an address decoder, takes the address delivered by the processor, and associates it with a slot. As long as that design is flexible, you should be able to shove a DIMM, into whatever slot you like. The BIOS figures out which slot is populated (by seeing the SPD chip on the DIMM). It then programs the Northbridge, to deliver chip select signals to that slot, in response to a particular range of addresses. On an AMD processor, with its integrated memory controller, if a chip select signal going to one of the slots is damaged, that could prevent the slot from being used. If that was the case, then a different processor would make the slot work again. If the slot pin is bent, then changing processors would not make a difference. For non-AMD processors, like say my old Pentium 4 motherboard, the memory controller is in a separate Northbridge chip. If slot #2 was broken there, and the slot connector looked undamaged, it could be the discrete Northbridge which is broken. A new motherboard might be required, to make slot #2 work again. If your motherboard is an AMD S754 board, with three slots, the bus connections are a little more complicated. Such a board has one data bus (single channel mode). But the address bus is split into two pieces. One address bus drives two slots, the other address bus drives one slot. The address buses carry the "1's complement" of each other, and only one address bus carries "valid" information at a time. Chip select signals tell the DIMMs, when their bus is valid. The purpose of that, is to make switching noises cancel, at the processor. For S754, the speed of operation the BIOS is willing to support, depends on whether one or two sticks are sitting on that one address bus. For retail motherboards, they may include a configuration table in the manual, showing what speed is possible with various RAM slot population patterns. If the motherboard is S939, people call it a "dual channel" board, but strictly speaking, it is not. AMD calls the operation of the board, either "64 bit" or "128 bit" mode. For older S939 processors, there are slot restrictions when using a single DIMM, due to those 64 bit versus 128 bit modes. Only two slots work in 64 bit mode, and the user has to know which slots those are. If the S939 processor is revision E or higher, the restrictions are removed, and any single slot can be used that you feel like. As you can see, when you don't provide details about the exact computer or motherboard involved, there are lots of choices and explanations possible. Memtest86 doesn't care where the memory lives. Memtest86 relies on the BIOS to set things up. All memtest does, is deliver addresses, and the hardware takes care of delivery, just like your Post Office. HTH, Paul |
#3
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Installing DIMMs, order of slots
In article , cyg says...
Actually, I do know that Memtest reports the speed of the chip differently depending on whether I put it in the first slot or the second slot. Then again, I am using an AMD processor with an integrated MC, so maybe it is also something to do with the CPU. Anyone have answers? Memory is addressed in banks. By putting them in the correct slot, they can be addressed in "dual channel" or "triple channel" mode thus increasing the throughput. -- Conor I only please one person per day. Today is not your day. Tomorrow isn't looking good either. - Scott Adams |
#4
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Installing DIMMs, order of slots
cyg wrote: There seems to be a common wisdom that one should always populate DIMM slots starting with the lowest-numbered slot. However, I've never seen an explanation as to why this is. I have reason to believe that my second slot may be faulty, but I'm not sure if Memtest will be affected by the fact that in order to isolate the issue, I can't have a DIMM running in the first slot. Actually, I do know that Memtest reports the speed of the chip Chip??? Don't you mean "module", that thing with all the memory chips soldered on it? differently depending on whether I put it in the first slot or the second slot. The only mobos I've seen that required a DIMM in the first slot were based on the Intel 810i chipset (815x may be the same). The slot shouldn't matter, even though the timings for each slot vary a tiny bit, but with marginal memory that could be enough to prevent proper operation. So maybe you should go into the BIOS setup and override the automatic memory timings and substitute the slowest timings allowed, including for the memory bus speed. Then if the DIMM works in your second memory slot, it means the slot is good but the memory isn't. Actually if the DIMM works with less than 100% errors, the slot is almost sure to be OK. Lots of retail memory is marginal now because it's made with chips that were either not fully tested (Kingston buys whole wafers, slices and packages them in-house, and apparently tests them at lower standards) or were rejected by the chip manufacturers (those chips are euphemistically called "untested" -- UTT). Your best bet is to stick with Crucial modules, which usually have Micron or Samsung chips on them, or test very thoroughly on your own and keep going back to the dealer until you get something that passes 100%. BTW, try to use more than one test program because I've never had an error reported by MemTest+ or Gold Memory 6.92 but lots reported by MemTest86 ver. 3.xx (MemTest+ is based on MemTest86) and Gold Memory 5.07 And don't accept memory that won't work perfectly at the BIOS automatic defaults. |
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