No banks, thnx. [LWN.net]

No banks, thnx.

Posted Sep 22, 2007 10:21 UTC (Sat) by khim (subscriber, #9252)
In reply to: banks? by sbishop
Parent article: What every programmer should know about memory, Part 1

While there are subtle differences between two-banks DIMM and two single-bank DIMMs (related to refresh as you've correctly pointed out) from software point of view they are more-or-less identical. I think this is why it was omitted from article. And the question "what the hell does latency 2.5 mean?" is common (less so today when DDR is almost history and DDR2 is mainstream, but still) so I think few lines are worth it...

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No banks, thnx.

Posted Sep 22, 2007 14:10 UTC (Sat) by sbishop (guest, #33061) [Link]

You're confusing the terms "banks" and "ranks."

Ulrich goes into quite a bit of detail about how an address is broken into a "row" and "column" component, but there is a third component, bank, internal to the DRAM.

A DIMM[1] can be single-rank or dual-rank. When you write or read a single-rank DIMM, you talk to every memory component on the DIMM, every time. Dual-rank DIMMs have double the number of components as a single-rank DIMM, and when you write or read (activate or precharge, for that matter) you only talk to half of the components.

What any of this has to do with software, I don't know. I work with some absolutely lousy programmers who know quite a bit more about memory than I do. :)

[1] I know this holds for unbuffered DIMMs, but I don't know about fully-buffered DIMMs. I don't work with those.