Bank Interleaving - Sandra accurate?

[G H Z]

Last nite I was testing a 2GB kit of GSkill PC4000 and Sandra was reporting Interleave as only 2-Way. This must not be correct if your in Dual channel (which I am), because there is no other BIOS setting relating to this right????

[chinkgai]

sandra is the most generic of generics and should not be believed when measuring performance

does cpuz say its dual channel?

[NightCrawler™]

Depends on what it is looking at..... dual channel is 2 ranks, 4 banks...?

NCâ„¢

[bachus_anonym]

2x1GB and 2x512MB will result in 2-way Bank Interleave. Only filling up all 4 DIMMs results in 4-way... and no, 4x1GB is not gonna be 8-way. At least not on DFI NF4... But I think, that 4-way could be supported on DFI NF4 and it's a matter of BIOS. Don't kill me If it's not true, though. I've been reading a lot about BI and still don't exactly understand when 4-way kicks in. I've read that in the past, on some mobos 4-way was supported even with 2x512MB...

[G H Z]

Interesting, I thought Opp was saying something about 8-way with 4 1024 sticks so I assumed 2 would give me 4-way on an RDX. Can you point me to where you read 2 sticks were good for 4-way on some mobo's bachus?

[bachus_anonym]

Interesting, I thought Opp was saying something about 8-way with 4 1024 sticks so I assumed 2 would give me 4-way on an RDX. Can you point me to where you read 2 sticks were good for 4-way on some mobo's bachus?OPP was hoping for 8-way with 4x1GB... ;) The article was, I think at LostCircuits... They had a board that would allow them to select 4-way, 2-way or Disable BI altogether. It was quite old, few years I think. I'll try to find it...

[high5]

2x1GB and 2x512MB will result in 2-way Bank Interleave. Only filling up all 4 DIMMs results in 4-way...
are you sure about that?

AFAIK bank interleaving does not depend on # of DIMMs. old socket A mobo's had bank interleaving option in BIOS, and IIRC i was even running 4-way with just one 256MB stick... long time ago. :)

[high5]

downloaded & installed Sandra:

http://img217.imageshack.us/img217/522/sandra5kc.jpg

as you can see, it reports 4-way in my case. i'm running s754, 2×512MB.

[bachus_anonym]

are you sure about that?

AFAIK bank interleaving does not depend on # of DIMMs. old socket A mobo's had bank interleaving option in BIOS, and IIRC i was even running 4-way with just one 256MB stick... long time ago. :)
Yeah, I know... I have tried and compared 2x512MB with 2x1GB at exactly same timmings and clocks and there is no performance gains where they should be If 2x1GB is 4-way. Like GHZ said, Sandra reports 2-way with 2x512MB and 2x1GB. With 4x512MB 2T or 4x1GB 2T (tested myself as well) it reports 4-way and there is slight gain in benchmarks compared to 2x1GB 2T.

That's why I totally can't understand the deal with bank interleaving on DFI NF4 S939. Especially after reading that article where they were playing with some old Abit mobo and had 4-way with 2x256MB. I kind of always thought that bank interleaving depends on amount of physical banks per IC (which are 2 for DDR and (at least?) 4 for DDR2 plus amount of physical memory banks on the mobo that are filled. To me, it's just very confusing :)

EDIt: I just took a shot of what Sandra shows with 2x512MB on my DFI NF4 S939: 2-way... So there yo ugo and figure it out :D We know that Sandra does not always show correct info (e.g. it reports 1T when TWTR=1 despite 2T being set) but in testing, 2x512MB is as good as 2x1GB, same performace at exactly same settings).


Your screenshot is from S754... Maybe that's why it reports it totally different :shrug:

[high5]

i'll try to pull one stick out and see what Sandra reports in that case.

it would be nice if someone with s939 board other than DFI could join the discussion. :)

and the thing i don't understand why is bank interleaving option not available in BIOS on K8 boards when we had that option on socket A mobos.

[high5]

pulled one stick out... now it reports 2-way.

http://img236.imageshack.us/img236/3690/sandra8qp.jpg

maybe this kind of behaviour is somehow IMC related. btw, is there any other tool that reads interleaving mode?

[G H Z]

I've been reading around a bit and have come to the conclusion that the only way to get 4-way interleave is with all dimm's populated on a 4 slot board. Here's a link with some professor talking about Interleaving, it clearly mentions the type of interleaving is dependant on the physical number of DIMM's.

http://csep1.phy.ornl.gov/ca/node19.html

Interleaved memory is a logical combination of two or more modules that are addressed as a single bank, similar to RAID in a way. Being that it is 'logical' it has the potential to be set by software/BIOS.

So Oskar got creative and added something to the 250GB BIOS that enabled interleaving. It's possible that if it's enabled in the BIOS when you only have one DIMM on the board Sandra will misread it.

[high5]

I've been reading around a bit and have come to the conclusion that the only way to get 4-way interleave is with all dimm's populated on a 4 slot board.
not quite. typical RAM module with 16 ICs has two banks. so if number of DIMMs, or better to be said # of banks, is relevant for interleaving then 2 modules are sufficient b/c there are 4 memory banks. my case supports this.

however it seems that things are a bit different in dual channel enviroment.

bachus (or anyone else), could you try putting 2×512MB in single-channel config on DFI nF4 and see what Sandra has to tell in that case?

[WeStSiDePLaYa]

i thought it was just number or total banks not dimms.

[STEvil]

Yeah, I know... I have tried and compared 2x512MB with 2x1GB at exactly same timmings and clocks and there is no performance gains where they should be If 2x1GB is 4-way. Like GHZ said, Sandra reports 2-way with 2x512MB and 2x1GB. With 4x512MB 2T or 4x1GB 2T (tested myself as well) it reports 4-way and there is slight gain in benchmarks compared to 2x1GB 2T.

That's why I totally can't understand the deal with bank interleaving on DFI NF4 S939. Especially after reading that article where they were playing with some old Abit mobo and had 4-way with 2x256MB. I kind of always thought that bank interleaving depends on amount of physical banks per IC (which are 2 for DDR and (at least?) 4 for DDR2 plus amount of physical memory banks on the mobo that are filled. To me, it's just very confusing :)

EDIt: I just took a shot of what Sandra shows with 2x512MB on my DFI NF4 S939: 2-way... So there yo ugo and figure it out :D We know that Sandra does not always show correct info (e.g. it reports 1T when TWTR=1 despite 2T being set) but in testing, 2x512MB is as good as 2x1GB, same performace at exactly same settings).


Your screenshot is from S754... Maybe that's why it reports it totally different :shrug:


2x512 DS = 4-bank
2x512 SS = 2-bank
2x1024 DS = 4-bank
4x1024 DS = possible 8-bank
4x1024 SS (yeah right) = 4-bank.

[omga14]

hmm this is interesting to me as i always thought BI was affected by double sided and single sided ram as well. ex, 2x512mb double sided ram would read as 4-way and 2x256mb single sided ram would read as 2-way. i'm trying to learn here so please don't kill me:D maybe Oskar did what he did for the 250gb so that some bandwidth was able to be gained without the need for dual channel capability. it isn't like having actual dual channels but i did see an increase in bandwidth with memtest just by enabling with the same bios settings for all else.

[bachus_anonym]

2x512 DS = 4-bank
2x512 SS = 2-bank
2x1024 DS = 4-bank
4x1024 DS = possible 8-bank
4x1024 SS (yeah right) = 4-bank.
And what is your reasoning behind it? Do you have any links for us explaining that in detail? If so, then please share it. According to above, what BI would be for 4x512MB SS and DS...?

If you mean "single-sided" as single-rank then as far as I know, there are no single-rank 1GB DDR modules that we could use on S939 or any other AMD platform. There are some single-rank 512MB DDR modules but they are rare (they are built of 8 IC in 64x8 configutratin). Whether ICs or on of the CB or both doesn't matter. Some manufacturers do that hoping to reduce noise and interference across PCB. I have 256MB of Kingston (chips one one side) and 256MB of Mushkin (chips on two sides) and they are both single-rank... ;)

@high5,

I can't find a way to fire up my rig with 2x512MB in Single Channel. But 1x512 shows exactly same as your S754. Then 4x512MB shows as 4-way, 2x1GB as 2-way...

[high5]

I can't find a way to fire up my rig with 2x512MB in Single Channel. But 1x512 shows exactly same as your S754. Then 4x512MB shows as 4-way, 2x1GB as 2-way...
in that case it seems that on K8 platform things go on per channel basis, i.e. you need 4 banks on each channel to run 4-way.

it seems as the only explanation why i'm capable of running 4-way with 2 sticks and you are not.

[STEvil]

SS/DS is just the more understandable way of saying SR/DR (as in everyone has been saying SS/DS since the KT133 days or so).

basically DS/DR needs 16 chips (on one stick). Yes, I also had some 2x256 Corsair BH-6 that were SR but chips on both sides.

You might need to set 2T to run single channel with 2x512.

4x512 (SR or DR?) showing as 4-way and 2x1gb 2-way may be due to the bios using "optimized" settings like how the Neo2 platinum used to adjust trc/trfc dynamically based on HTT/divider.