Technology, Support, and News Forum

[~Robrowe~ Profile Website]

When it comes to memory, you can have mixed speeds in a system, but say you have one PC2100 and one PC2700, the PC2700 will automatically be downgraded to running at PC2100, in single channel.

As for mixing memory using dual channel. You cam mix different vendors, as long as the memory is the same size and speed. However, it is HIGHLY recommended that you use the same vendor as well, since reliabiliy issue will come into play otherwise.

One final note. When it comes to speed, PC3000 is just a made up speed. there is no spec for PC3000 and definately no JEDEC standard. What module makers have done is overclocked a PC2700 chip to run at the equivilant PC3000 speed or whatever other PCXXX speed the choose. 333mhz running at 375 mhz or whatever.

This is why you see memory modules sold sometimes with a big heatsink across the DRAM chips. It is just an overclocked chip.

Every stick of ram I buy has a heat spreader, its not because the the memory is overclocked it is so you can overclock it and use higher Vdimm settings to keep it stable. The heat spreaders dissipate the added heat.
PC3000 is the common name for the JEDEC specification for DDR which runs on a 183MHz bus speed (366MHz double data rate). The chips themselves are named in a more conventional way as "DDR-366" where the name reflects their MHz speed. The modules, however, are named for the effective data transfer of 3000 MB/sec (3.0 GB/sec) on a 64-bit bus.PC3000 DDR uses DDR-366 chips. These modules are programmed for CAS 2.5-3-3 operation at 366MHz via the serial presence detect (SPD) EEPROM. PC3000 DDR is designed for use with motherboards supporting the PC3000 spec and CPUs which run on a 133MHz FSB (266MHz DDR) and yet to be released CPUs running on a 183MHz FSB (366MHz DDR). While no CPU was designed for a 183 Mhz FSB this was an interim design which is very popular with memory modules, much like the ones available today capable of much faster speeds than current stock FSB supports. Dual channnel design is very picky and every motherboard manufacturer specifically states to use modules of the same manufacturer and model as chip configurations vary. Most recommened a matched set. Please research JEDEC STANDARD Double Data Rate (DDR) SDRAM Specification JESD79C ( Revision of JESD79B)

[rjz Profile WebsiteYIM]

I had to return my 512 PC 2100 DDR and get some go Centon ram. IS it ok if I mix it with the other OEM ram or does that company have known problems with the other ram? Does the bigegst stick always go in the 1st slot by the processor?

[pollocktodd Profile]

No major DRAM maker manufacturers 366mhz DRAM devices. Yes, the heat spreader to to dissapate heat, and this is because the device is overclocked to begin with. You will notice that companies like Corsair come out with these modules (eg. PC2400, PC3000) not too long after speeds like 266mhz or 333mhz are available. Since these companies do not even make DRAM (Corsair, Kingston, Crucial (division of Micron)), they have to come up with a marketing ploy to sell a "premium" product at premium prices, usually for gamers.

As for JEDEC specs, I assure you that there is no JEDEC standard for PC3000. There are standards for PC1600, PC2100, PC2700 and PC3200.

The current spec is JESD79D, a revision of JESD79C, and the speed of DDR SDRAM are outlined on page 9. These are speeds of actual DRAM devices, not the over clocked module designation.

Please research JEDEC STANDARD Double Data Rate (DDR) SDRAM Specification JESD79D ( Revision of JESD79C) and you will see there is no mention to the PC3000 speed, as no one in the industry makes 366mhz devices. These are one of two things. Over clocked 333mhz devices, or 400mhz devices that when tested on the wafer just didn't make the cut to run at 400mhz.

As long as the SPD content match with one another from vendor to vendor, there should be no problems with mixing vendors with the same modules. I have yet to see a problem. The only thing that may happen is running into a device problem (ie. retention issue), but in this case, even with the same vendor, stability problems can occur.

They recommend the same vendor so unfamiliar end user do not inadvertently buy two different modules with one uniquely different attribut. (ie. CL2.5 and CL3), which in this case, you would end up running single channel, although after discussion with designers, if BIOS developers implemented the design, the motherboard should theoretically be able to down grade the memory and run both modules in dual channel. Thats a whole other discussion though.

One last thing, almost every good yield of DRAM device can be overclocked. The problem is how good of a device it is to begin with when coming out of the wafer. One wafer can produce DDR400 devices for example, but at the same time, the devices that not meet DDR400 on the wafer are not just thrown out. There are sometimes made into DDR333 devices, or in the situation of say Micron, branded under the name Crucial, so they can still sell the parts, but not worry about effecting qualifications at there OEM customers, simply put.

One last thing, CAS Latency is defined as CL2, CL2.5 or CL3 not CAS, since the Column Address Strobe is part of a broader array (including RAS), it is impossible to define a value simply for CAS....FYI

Regards.

[imnuts Profile Website]

thanks for that thorough description. learned a lot more about ram. Didnt know that theoretically the mobo should be able to run two dimms of different ram in dual channel, kind of interesting.

[pollocktodd Profile]

Well, I have not seen it in a working configuration, but assuming you have 2 of the same technology modules and the device are the same, as well as same size and density, a 400mhz and a 333mhz module could run dual channel in the same system, if the BIOS was to downgrade the speed of the 400mhz to 333mhz. I highly doubt we will ever see a mobo do thing however, since they (as well as memory makers) are in the business of making money by selling new products! Just wait until DDR2 becomes mainstream and everyone as to by a new mobo to even get the memory to boot!

Again, just my two cents!!! *L*

[~Robrowe~ Profile Website]

pollocktodd, I am not trying to get in a shootin match here but my post above for the most part was excerpted directly from the JEDEC standard JESD79C. The D revision may omit the DDR366. As for the CAS thing I somewhat agree with you on CL. For CAS latency. My post above with that reference was derived directly from the JEDEC DOC via copy paste so if it is a lie then they told it. As far as running ram in dual channel configurations refer to your motherboard manufacturers site and check their recommendations you will find that running two different sizes may work but it will default the larger stick of ram to the size of the smaller stick.
There are many issues involving dual channel setups and mixmatching sticks is a gamble at best. There are many ram manufacturers who make matched sets that have been tested, proven and guarenteed to work or your money back. The ones that havent been will not refund your money and will simply tell you that it is not their fault that their memory does not work in your mother board.
Do a little research before making your decision. I made that mistake myself and have two sticks of kingston ram with the exact same specs bought from the exact same place on the exact same day sitting on a shelf collecting dust as they would not run in a dual channel config on an asus A7N8X rev2 deluxe motherboard and the matched corsair that is on the recommended list went to working with out a hitch. JEDEC only writes a standard and most of the memory available and in use today is not on their list.

Could you please post a link to the "d" revision because I cant seem to find it, several search engines came up empty handed with the search JEDEC JESD79D.

[pollocktodd Profile]

I neither want to get into a shotting match, but I did want to post without being corrected for something that was already correct. It is true, you cannot mix SIZES, but mixing SPPEDS is what my hypothetical post referred to. I appologize if I did not come across clearly.

All of my suggestions are based upon experience with memory and on the experience of memory designers. I work for a major DRAM player and test extensively these odd ball configurations. I definately agree that dual channel is very picky. I just wanted to inform that different configurations are possible, but like you said, not manufacturer recommended.

Oh, here is the link to JESD79D. You will have to be logged on to JEDEC to get it. If you do a search on the JEDEC website using JESD79D, it will bring you right to it as well.

http://www.jedec.org/download/search/JESD79D.pdf

Regards.

[Tirian13 Profile]

here's what i've experienced in the ram department...

i've use PC133 in a PC100 mobo, used PC2700 on a PC3200 board
PC3200 on a PC2100 board


all worked just fine with no problems, i've even used different brands of ram at the same time, only thing i never tried was different speeds, but i imagine you wouldn't have a problem mixing speeds, you'd only get the benifits of the slowest stick i'd amagine

[~Robrowe~ Profile Website]

I neither want to get into a shotting match, but I did want to post without being corrected for something that was already correct. It is true, you cannot mix SIZES, but mixing SPPEDS is what my hypothetical post referred to. I appologize if I did not come across clearly.

All of my suggestions are based upon experience with memory and on the experience of memory designers. I work for a major DRAM player and test extensively these odd ball configurations. I definately agree that dual channel is very picky. I just wanted to inform that different configurations are possible, but like you said, not manufacturer recommended.

Oh, here is the link to JESD79D. You will have to be logged on to JEDEC to get it. If you do a search on the JEDEC website using JESD79D, it will bring you right to it as well.

http://www.jedec.org/download/search/JESD79D.pdf

Regards.

Thanks for the link. I will look at it later.