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As seen below (Figure 1), I have two 512MB sticks in alternate slots (one channel) and a 1GB stick in one of the remaining slots (a different channel). This is on an Asus P4P800.

When I boot, it says that it is running in Single-Channel or Virtual Single-Channel mode. I have searched everywhere but cannot find any information on what the heck “virtual single-channel” is. The only references that I can find are simply mentions of it by people trying to get dual-channel working as opposed to wanting to know what “virtual” means.

My best guess is that it is a synonym for either asymmetric dual-channel (which seems to apply here) or dual-channel interleaved (which does not). I cannot find anything about the P4P800 supporting either of those modes however, so I really have no clue what virtual single-channel could be.


Figure 1: RAM configuration on a P4P800

[    512MB    ] (Blue)
[     1GB     ] (Black)

[    512MB    ] (Blue)
[    -----    ] (Black)
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Nice, this question is already the third Google result—not on Bing or Yahoo! yet—so hopefully other (if any) people who want to know will get an answer much faster than I did (I first searched a few months ago). –  Synetech Feb 28 '12 at 23:01
    
Oh, and I tried both arrangements: ½GB-1GB--½GB-0 and ½Gb-½GB--1GB-0, but they both gave Virtual Single Channel. I guess that this board doesn’t support “dual-channel interleaved” and I’ll have to find a 1GB stick; too bad they remain expensive for some reason. :-( –  Synetech Mar 7 '12 at 17:49

1 Answer 1

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Doh! I figured it out (sometimes less is more). Not surprisingly I suppose, the answer was in a tech-doc.

Apparently the confusion is due to terminology. What happens is that there are two causes for a system running in single-channel mode. In both cases, the memory does not use the multi-channel architecture it supports, but the specific cause of using a single-channel determines the actual label.

When only one slot of a channel has RAM in it and the other is empty, it is called “single-channel” mode. When both slots of a channel (or more in the case of triple- or quad-channel boards) have RAM in them, but they are not matched, that is called “virtual single-channel” mode (though many people just call it single-channel, thus causing all the confusion).

In other words (or pictures as the case may be), on a two-slot motherboard (for simplicity):

Single-Channel:
[    512MB    ]
[    -----    ]

Virtual Single-Channel:
[     1GB     ]
[    512MB    ]
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Some architectures, at least the newer Intel ones, are able to put themselves into a mixed mode when the RAM slots are mismatched. For example, with a 4 GB stick and a 2 GB stick it will work in dual-channel mode for the lower 4 GB of memory and single-channel mode for the upper 2 GBs. –  wingedsubmariner Oct 16 '13 at 19:03

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