PSU and RAM question

[DrPop]

I've got two more 3930K rigs to build up now...
PSU: Should I still look to run at about 50% of the PSU rating? I remember back in the day that was a sweet spot, but maybe things have changed? Thinking 150W CPU + 250W GPU allowances = ~400W draw, so 750W to 800W rated PSU, that sound right?
Also, is it worth the extra $ to get a platinum over a gold? I saw a big difference between going with an 80 Plus gold and anything lower, so Gold is the lowest I'll go, just not sure about ponying up more for platinum or not?

These X79 mobos have 4 channels (8 slots) for RAM, so am I better off running 4 x 4GB sticks over 2 8GB sticks? Does that theoretically increase the RAM speed or bandwidth?

The two rigs will sit in the back of the office and just crunch 24/7 so just one GPU a piece and nothing else connected but a small SSD each.

[scole of TSBT]

For DIMM config, I believe you are correct and want 1 DIMM per channel, assuming both mobo and CPU support 4 channels. Any less and you're not taking advantage of all the channels. Any more and you're over loading a channel.

For PSUs, it looks like there's about a 2% difference in peak efficiency between Silver and Gold and 2% between Gold and Platinum. Peak efficiency is at around 50% for all. Here's chart I found...
http://i.imgur.com/A0vbvIj.png

[Bryan]

Use 1 stick per channel and use all 4 channels.

[DrPop]

Awesome, thanks guys!:)

[Mumps]

So, you just wanted a refresher? Wanted to type more rather than doing a search? :))

http://www.setiusa.us/showthread.php?5383-Power-Supply-Efficiency-80-PLUS&highlight=platinum

[DrPop]

So, you just wanted a refresher? Wanted to type more rather than doing a search? :))

http://www.setiusa.us/showthread.php?5383-Power-Supply-Efficiency-80-PLUS&highlight=platinum

Yeah, I think I was in a Chatty Cathy mood for once, not my usual these days on here, I guess. ;) Mostly though, I was looking for opinions on the 50% of max rated PSU that we used to run at. Wasn't sure if the new PSUs were more efficient, for example if you could run at maybe 60% of max load and get what we used to get at 50%, then you could use a smaller/cheaper PSU. Doesn't seem to be the case. So I think I'll go somewhere 800W or North of that just to be safe. Never know what GPU I might throw in there down the road.

Doesn't really seem to be much difference - a few percent - from Gold to Platinum, but I might do it just for less heat, etc. Every little bit has got to help.

Edit: on the RAM side of things, anyone messed with going up to DDR3 2400 speed RAM instead of the regular 1600? Would there actually (even theoretically?) be a credit increase per day, or is the RAM speed such an insignificant part of crunching as to be irrelevant on a dedicated cruncher?

[John P. Myers]

Yes 60% is fine. Not really a loss until you go over 70% and that loss isn't more than 3% efficiency even if you peg draw at 100%. With Cali electricity prices, you might want that 3% though ;)

Additional RAM speed over 1600Mhz isn't useful on X79 since it increases latency.

[Bryan]

Additional RAM speed over 1600Mhz isn't useful on X79 since it increases latency.

Not only that, the higher clock rates that you pay really good money for get downclocked ie 1800MHz memory runs at 1600 as does 1600M RAM so the extra is a waste. The same is true of the higher clock rates ... they get downclocked as well (not to 1600 but below their potential). ASUS says it is because of the CPU.

Check in the MB manual and you'll see what I mean. Personally I wouldn't go beyond 1600 ... it's wasting money. Spend the extra on water cooling and then clock the heck out of the CPU.

[DrPop]

Huh, that's bizarre. So something doesn't work the same with X79 as it does with the regular i7 rigs then, because they advertise the motherboard going all the way up to DDR3 2400. Oh well. So what I want is DDR3 1600 with the lowest CAS numbers, right?

[John P. Myers]

So what I want is DDR3 1600 with the lowest CAS numbers, right?

Correct. But also not more than 1.5v

[Bryan]

Huh, that's bizarre. So something doesn't work the same with X79 as it does with the regular i7 rigs then, because they advertise the motherboard going all the way up to DDR3 2400. Oh well. So what I want is DDR3 1600 with the lowest CAS numbers, right?

The MB supports up to DDR3 2400. However, look at page 2.-6 of the manual ... " Due to Intel CPU behavior DDR3 2200/2000/1800 MHz memory modules will run at DDR3 2133,1866/1600 as default."

It may be you can manually make them run at their real freq but if you select DDR3 1800 in BIOS it says it will run as 1600. Since the MB supports 2400 and that isn't shown on page 2-6 maybe that will run at speed.

You're better off watercooling and running the CPU at 4.5G like Al is doing. I doubt you can get away with air cooling at that freq. Then again, I never tried it :D

[John P. Myers]

Looks like it's rounding the RAM speed down to the closest multiple of 266MHz. That means 2400 should run at 2400, but the extra latency isn't worth it. Going beyond 1600MHz with DDR3 hasn't shown any improvement for the extra money.

DDR4 is a different story. 3200MHz is the sweet spot there right now.

[DrPop]

OK thanks, that clears that up. Any reason other than power savings to get the RAM at 1.5V over the 1.65V sticks? I honestly don't know what difference that makes other than using 0.15V less?:confused:

[John P. Myers]

1.5v is JEDEC spec. 1.65v is 10% above spec and just means you're paying extra for factory overclocked RAM. And it'll run much hotter. The best latencies are available in the standard 1.5v

[DrPop]

Thanks! Makes perfect sense, I appreciate it. :)