I don't get this FSB:DRAM Ratio Stuff

The magic smoke.

Moderators: phlip, Moderators General, Prelates

User avatar
big boss
Posts: 589
Joined: Tue Mar 23, 2010 7:59 am UTC

I don't get this FSB:DRAM Ratio Stuff

Postby big boss » Thu Jul 26, 2012 9:53 am UTC

Ok so I just built a pc recently here are the specs:

Windows 7 x64
ASUS SABERTOOTH Z77 LGA 1155 Intel Z77 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboar
Intel Core i5-3570K Ivy Bridge 3.4GHz (3.8GHz Turbo) LGA 1155 77W Quad-Core Desktop Processor Intel HD Graphics 4000 BX80637I53570K
EVGA 015-P3-1480-KR GeForce GTX 480 (Fermi) 1536MB 384-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
CORSAIR Professional Series HX750 (CMPSU-750HX) 750W ATX12V 2.3 / EPS12V 2.91 SLI Ready CrossFire Ready 80 PLUS SILVER Certified Modular Active PFC Power Supply
Western Digital Caviar Black WD1002FAEX 1TB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5" Internal Hard Drive -Bare Drive
NZXT Phantom PHAN-001RD Red Steel / Plastic Enthusiast ATX Full Tower Computer Case
CORSAIR Vengeance 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1866 (PC3 15000) Desktop Memory Model CMZ8GX3M2A1866C9R
ASUS Black 12X BD-ROM 16X DVD-ROM 48X CD-ROM SATA Internal Blu-ray Drive Model BC-12B1ST/BLK/B/AS - OEM $

So I noticed the cpu was hitting around 75 degrees C under load with the turbo turned on running at 3.8 ghz. So I turned off the turbo and now according to CPU-z the cpu is running at 1.6 ghz even though the only things I did were turning off the turbo. Also according to my temperature utility the cpu is at 1 degree C, so not sure whats happening there. So how do I increase the speed? I notice the dram speed is only 1333 when its rated for 1866 so i manually set it to 1866. I was reading online about this FSB:DRAM ratio stuff and got extremely confused so any help would be appreciated.
"Starbuck, what do you hear?"
"Nothing but the Rain."

User avatar
mosc
Doesn't care what you think.
Posts: 5401
Joined: Fri May 11, 2007 3:03 pm UTC

Re: I don't get this FSB:DRAM Ratio Stuff

Postby mosc » Thu Jul 26, 2012 4:48 pm UTC

pretty sure all the IVY bridge chips run a 100mhz core clock. All the clockrates you're throwing around are basically just multipliers on top of that. 3.4ghz? that's a 34x 100mhz clockrate. The multiplier is adjusted. The i5-3570k is given a multiplier that varies as performance and power consumption change between 16-34x (38x with turbo). If you're getting 1.6ghz, it would seem to be fully throttled down when you looked. Maybe this helps?
Image
from: http://www.tomshardware.com/reviews/cor ... 204-2.html

It is my understanding if you want it to hold a clockrate you'd need to turn off the power savings mode and the turbo mode. It'd hold at 3.4ghz unless the TDP was violated and then it would throttle back whither you wanted it to or not out of self-preservation.

DRAM is typically driven by a separate clock, multipled, and double pumped for DDR (dual data rate). The memory's multiplier is locked in the chip. The northbridge (these days internal to the processor) adjusts the DRAM clock, generally some multiple of the core clock, such the the memory speed can be adjusted. Motherboards sometimes fail to recognize the dram clock rating on various memory DIMMs (which often come out well after the motherboard was designed) and can default to clocks that are "rated". DRAM is notoriously horrible about being slow with official speed standards and is most often advertised with it's maximum frequency, not what the actual "official" stamp on the chip says. What does this mean? It means that the motherboard needs to be told what to do with the memory and when it gets confused, it will default to the often considerably slower "rated" stamp on the dram. In this case, your dram clock is probably a multiple of 133mhz (double pumped makes this effectively 266mhz). Your memory can handle a 7x clockrate but the stamp on the chip says 5x. Your board is flexible but will default to the 5x133x2 (1333mhz) value if it does not recognize the specific DIMM module and know to use a 7x multipler.

EDIT: In the "good old days", the core clock was consistent across the board. The FSB (front side bus) was a speed to reflect the underlying clock of the cpu (which would have a fixed multipler, say 10x FSB) and the memory (often 1 to 1). Overclockers, unable to change the CPU's multiplier, would adjust the FSB to overclock the chip. This would speed up the northbridge and memory as well. A common motherboard trick was to use a fancy northbridge to separate the memory clock from the FSB as some multiple allowing a somewhat independent adjusted memory clock. The FSB term stopped meaning much when the northbridge was brought inside the processor and the memory clock was no longer tied to the CPU clock. The interface between the cpu and the main system memory is now direct without FSB coursing through the motherboard.
Title: It was given by the XKCD moderators to me because they didn't care what I thought (I made some rantings, etc). I care what YOU think, the joke is forums.xkcd doesn't care what I think.

User avatar
big boss
Posts: 589
Joined: Tue Mar 23, 2010 7:59 am UTC

Re: I don't get this FSB:DRAM Ratio Stuff

Postby big boss » Fri Jul 27, 2012 4:50 am UTC

Thanks for the response. Apparently I only turned the turbo off so hopefully that will fix it. A few more questions.

1. Is there a setting somewhere to change the dram multiplier to X7 for 7x133x2 value? I've looked in bios and can't find any. Or would it be better to just leave it the default settings?

2. If any1 happens to know anything about the sabertooth z77 mobo or its integrated sound codec: Many of my games have been freezing (just the game not the computer), so I disabled the integrated soundcard and I have gone 4 hours without any crashing. Drivers up to date and everything. Should just buy a new soundcard? I've read somewhere that the oc on the cpu caused by the turbo (and apparently the power saving mode) can cause issues and I'm currently testing that, just wondering if anyone has some suggestions.

edit: One more thing. Once I turn off the turbo and power saving mode, how do I underclock the cpu? Can't really find a guide anywhere I can follow.
"Starbuck, what do you hear?"
"Nothing but the Rain."

User avatar
mosc
Doesn't care what you think.
Posts: 5401
Joined: Fri May 11, 2007 3:03 pm UTC

Re: I don't get this FSB:DRAM Ratio Stuff

Postby mosc » Mon Jul 30, 2012 4:38 pm UTC

1. No, you set the speed. It's changed some in recent years with integrated northbridges inside the CPU's (more accurately, there is no northbridge anymore). You tell the motherboard in the bios the speed of the memory and if the CPU can deal with it, that's what it'll use. If the memory module is not an officially stamped for it's rating dimm (which few higher end sticks are) and the motherboard hasn't been specifically programmed for that specific dimm, the speed must be set manually or it will default to something slower that the chip was stamped with. The multiplier

2. never heard of this before

3 (EDIT): Most CPU's do not allow multiplier changes manually. AMD sells a special line of "black" chips which have an "unlocked" multiplier, allowing manual adjustment. Intel has made unlocked chips before (extreme edition notably), but most of them are locked. You can adjust the core clock in most motherboard's BIOSes. It may affect other stuff beyond your CPU, but this is the main overclocking option with a locked multiplier chip.
Title: It was given by the XKCD moderators to me because they didn't care what I thought (I made some rantings, etc). I care what YOU think, the joke is forums.xkcd doesn't care what I think.

User avatar
Endless Mike
Posts: 3204
Joined: Thu Dec 06, 2007 3:04 pm UTC

Re: I don't get this FSB:DRAM Ratio Stuff

Postby Endless Mike » Tue Jul 31, 2012 12:55 pm UTC

mosc wrote:3 (EDIT): Most CPU's do not allow multiplier changes manually. AMD sells a special line of "black" chips which have an "unlocked" multiplier, allowing manual adjustment. Intel has made unlocked chips before (extreme edition notably), but most of them are locked. You can adjust the core clock in most motherboard's BIOSes. It may affect other stuff beyond your CPU, but this is the main overclocking option with a locked multiplier chip.

All K series CPUs, such as his 3570K have unlocked multipliers.


Return to “Hardware”

Who is online

Users browsing this forum: No registered users and 41 guests