Re:what is Quad Channel Memory?
Thursday, January 05, 2012 9:29 AM
The answer to this question is a little complicated. The "channel" status of memory doesn'tper se have anything to do with the memory itself: it has to do with how many dimms of ram can be read/written to by your CPU's (or on some boards, chipset's) memory controller.
For example socket 1155 cpu's have memory controllers that are "dual channel". This means the following:
A. The computer can effectively use 2 dimms of ram
simultaneously (and as a result)
B. you should install at least two dimms and you should always install in multiples of 2 (i.e. 2 dimms, 4 dimms, 6dimms, 16 dimms . . . etc) and
C. If you install less than two dimms (or not-identically spec'd dimms) or if you install an odd number, expect performance degradation (relative to what your memory
controller would be capable of if you matched its channels properly)
There are also triple (x58) and quad (x79) channel memory controllers out there that get better memory bandwidth than dual channel because they can read three or four dimms simultaneously as opposed to only two. However with triple channel you need to install at least three dimms and in multiples of three (3, 6, 9, 12, etc) and with quad channel in multiples of four (4, 8, 12, 16, .....)
So what does it mean when memory is advertised as being "quad channel"?
A. It may mean any or all of the following:
A. It is a kit of four dimms
B. It may have an xmp profile (xmp profiles allow dimms to run at their
rated specs without you having to enter the timings, voltage and clockspeed manually) that is compatible only with or especially with the x79
cpu memory controllers
C. It may have been tested by the manufacturer and been confirmed to run
at its rated speed, timings and voltage in a quad channel configuration.
Q. So what happens if you put a "quad channel" ram kit into a dual channel platform (like socket 1155 / 1156, etc)?
A. You will be running in dual channel, will not receive the benefits of quad channel vs dual channel (i.e. double memory bandwidth) but will not be penalized performancewise because 4 dimms is a multiple of 2 and therefore compatible with dual channel memory controllers without penalty.
Q. So how can I run a quad channel kit in quad channel configuration?
A. Buy a motherboard that has or supports a cpu that has a quad channel memory controller?
Q. Are there any other considerations I should be aware of when running a kit marketed as quad channel on a dual channel (sockets 775, 1155, 1156, some others) or triple channel (x58) channel system?
1. (applies to dual and triple channel): You may have to enter your voltages, timings and clockspeed manually because the XMP profile in the quad channel kit may not be compatible with your system. If you know how to do this or think you can figure it out by tinkering or asking on the forums, this should not be a problem.
2. (applies to dual and triple channel): The ram may not have been tested to run in your configuration so you may have to run it at a slower / higher voltage / tighter timed setting. It is also possible that you will be able to run it at better settings as well. The point is: when they came up with its rated specs it was probably based on a test using it in its stated channel configuration.
3. (applies to triple channel): You will incur a performance penalty if you use four dimms. You will have to waste one of them (to get it to three) or buy two more (to get it to six) to avoid the penalty.
Q. What if I buy a triple or double channel kit for my quad channel sli system?
A. You will suffer a performance penalty if you do not buy one extra (identical) dimm for the triple channel kit (to make it 4 dimms) or an extra (identical) double channel kit (to make it 4 dimms). It is also quite probable that you may have to lower its stated specs because those specs were based on tests with 2 or 3 dimms, not four. Also, the xmp profile will probably be incompatible and you will have to enter settings manually.
SUMMARY: Other than XMP profiles and Spec testing there is no real difference in the actual dimms between double, triple and quad channel ram. Make sure you insert the appropriate number of dimms into your motherboard based on your memory controller. If you need to rely on xmp profiles or want ram tested for your particular configuration, it is best to buy a kit marketed for your particular channel configuration.
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