Single rank or bank modules are usually faster. I don't know if it's still true, but there used to be a limit in the number of banks a computer could access. The dual rank modules use smaller (read older, more power hungry) chips. DO NOT mix modules with different ranks.
Older systems cannot use Dual or Quad Rank ram.
This is a Chipset and bios limitation.
This vendor has guaranteed compatible ram
Thats why LOW Density Ram is required for MANY Intel Chipsets.
Any ole joes crab shack ram isnt compatible. If you get it from cruical or from dell its guaranteed to be compatible. The speed you need depends on which cpu you have and its FSB. Ranks count also you cannot mix single rank and 2 rank and 4 rank ram. Its not required but being all from the same vendor for the sets of 3 helps. There are also processors that the motherboard supports that do not support ECC ram.
YOU CANNOT USE 8 GIG Dimms ever. Nor can you use Registered and or Buffered Ram. Crucial doesn't seem to show 4 gig dimms working either.
I am upgrading to 8GB RAM. This will be 2x4GB of DDR3 PC3-10600 memory. For performance, which is better, single rank or dual rank memory. Just how much difference is it likely to make?
Thanks for the reply. I don't think this machine fits the 'older' profile. I believe it supports Dual Rank Ram. The setup guide (page 60/61) doesn't say so explicitly, but the service manual (page 38) shows that the system settings can be "Single" or "Dual". I checked my settings and it is reporting Dual - it's not an editable field. Those manuals also confirm the chipset as H61.
I followed the link for the crucial website, and when clicking 'View more compatible memory upgrades' it does in fact offer 4GB Dimm support. Following the 2x4GB link, irritatingly the specification does not specify the rank for this memory. However, googling the product key takes me to here, which does specify rank as 2.
Now, as far as I can see, neither Crucial or memorystock offered 1R memory as an option for upgrade. However, following the memory selector on Kingston lead to this. This is documented as single rank memory.
So, I'm still left with the original question, what are the performance characteristics of using single vs dual ranked memory for this machine?
Single rank is faster than two or four.
What you are referring to in the Service Manual is NOT rank but Channel. Dual channel is automatic and operational if there are matched pairs of modules in paired sockets. Single channel is a single module or unmatched modules. Dual Channel is faster than singe channel. Rank is the number of groups (for a better word) on a module. Dual channel is often dual sided modules using low density (cheaper) RAM chips that require separate addressing by the processor. You can not mix single and dual modules, and using dual rank nodules often limits the amount of RAM possible. Dual rank modules are usually used in servers that have huge amounts of RAM, but can also address lots of RAM.
LOW DENSITY and Chipset north bridge limitations are the issue. This is why 16 or 32 gigs is not possible. You also cant mix ranks.
In later cpus like the I7 the north bridge and video are integrated into the processor.
Fair point on channels, my error. On the topic of density, I note this is not quoted on so many occasions, both on the big vendor sites and elsewhere. Also, I note some are of the opinion that the definition of density is imprecise, with what is now regarded as low density, may have been regarded as high in the past.
What is the clear specification for this PC, for what constitutes compatible LOW density RAM and likewise the specification for incompatible HIGH density RAM?
There is no clear specification. No one size fits all for all models all occasions. You have 2 slots and 4 gigs is the max for any Dimm.
4GB Dimm for Dell Inspiron 620
(DDR3-12800 240 pin - Non-ECC Low Density Non buffered)
The density of a memory module is basically determined by the DRAM chips that make up the memory module. For example a 1GB DDR3 module like the one in your system can be made up of 8x 1Gb (gigabit) chips or 16x 512Mb (megabit) chips. The fewer chips on the module, the higher the density. Parts that have 2 or 4 or 8 chips instead of 16 or 32 can be High density. The same is true for ranks. 4 rank modules tend to be for boards that support 32 gigs or more with 4 slots not 2 for memory.Symptoms of Density and Rank incompatibility range from only seeing HALF of the ram installed to not working at all.
This is not as complicated as being presented. Most computers are set up to support a certain number of Ranks.. Four slots of RAM means four ranks are supported, and the modules are built for this So if you use dual rank chips, you reach the limit with half the slots filled.
In addition, dual rank chips were designed for servers, where scads of RAM are necessary, and dual rank chips allowed double amounts of memory on each board. I have never seen a spec for a non-server computer to use dual rank chips. There is no reason that system boards couldn't be built to accommodate dual rank, but I think being able to use either type would complicate the board. In addition, at least in the past, most dual rank modules offered for sale at low prices were USED, having been pulled from old servers. High density single rank modules are not that expensive