Highest spec DDR RAM that is backward compatible w PC2100?

[Shuomaru]

I want to upgrade RAM in my pc (Athlon 1GHz with 128MB PC133 SDRAM). I have two slots for SDRAM and two slots for DDR which can not be used at the same time. Maximum size for each type is 1GB. I decide that I want to use DDR for all the benefits over SDRAM. I may get 512MB or 1GB but it has to be PC2100 DDR. However PC2100 is getting harder to find since it's the lowest spec of DDR. Also, I would like to use these DDR for the next motherboard and chipset so I want to get the highest spec which is still backward compatible with PC2100.

Is this possible? I know only few RAMs are backward compatible. Or I have to get PC2100 exactly?

Thanks

 

[stevty2889]

Any DDR above pc2100 will work, you could get pc3200, and it will be completely backwards compatible to pc2100 speeds.

 

[Concillian]

I wouldn't buy PC2100, mostly because of it's limited lifetime.

PC2700 and PC3200 is 100% backward compatible with PC2100. ANY 184-pin DDR is backwards compatible. PC3200 shouldn't be too much more expensive, and will be compatible with many upgrade options should you choose to move to a new motherboard with an AthlonXP or an Athlon64.

 

[Aeridyne]

i have a question to float in on this topic guys. what if you used say pc 5000 or whatever one of those outrageous speed ones above 3200. will it still be backward compatible.

question 2. if i used a socket 939 athlon 64 3000+ it would have an 800 mhz bus right? so if i got faster than 3200 ram would it automatically go faster without doing anything in the bios or overclocking anything?

if not automatic could you set it manually and not have to worry at all?

 

[slash196]

I think the higher speeds are DDR2, which is 240 pin, so no, it won't be backwards compatible.

EDIT: 184 pin is pc-4500 and below.

 

[Nyati13]

question 1 : The PC4000 or whatever (Make sure you don't buy the DDR2 which can have PC**** numbers the same as DDR) will be compatible, but it will run at PC2100 in your current board.

question 2 : The s939 3000+ uses a 1000MHz HT Link, but that is not the HTT clock. If you install everything, and set the motherboard to use defaults, it will run the HT Link at 1000MHz like it is supposed to, and it will run the RAM at it's rated speed (ie PC2100, PC2700, or PC3200). If you buy higher than Jedec spec RAM (ex. PC4000), the board will run it as PC3200, unless you overclock.

 

[TerryMathews]

Originally posted by: stevty2889
Any DDR above pc2100 will work, you could get pc3200, and it will be completely backwards compatible to pc2100 speeds.

It's supposed to be.

Every now and then, though, memory pops up that won't work properly if it's refreshed at too slow of a rate. I believe BH-5 suffered from this - wouldn't work at CAS3?

There's a technical explanation about why this happens - has to do with each memory cell being little more than a capacitor.

I guess what I'm trying to say is that "It should work" but if you run into problems, try a new piece of memory first.

 

[Aeridyne]

thank you nyati, ive been trying to figure that out since yesterday.

ive also been doing a little research on overclocking. how do you know if your board has an agp/pci lock? and i see tons of people doing OCing, but in the intro guide it says you can get errors and data corruption. The machine i am thinking of OCing is my main rig and has all of my files on it that i have been collecting for years. i have made backups of what i can but not everything will fit on what ive got. so i want to know what the real risk is. anyone....

 

[mechBgon]

One other gotcha: some (actually, most) PC3200 and faster is spec'ed for 2.6 volts or higher. Some of Corsair's stuff is spec'ed for 2.75V. If you throw that into a mobo whose only option is vanilla 2.5 volts... good luck Instability, here we come.

So for a board that has no voltage adjustments, and can only do 2.5 volts, I would think about sticking with PC2700, which always seems to be spec'ed for 2.5 volts. Maybe that's a little conservative, what do you guys think?

 

[jiffylube1024]

Originally posted by: mechBgon
One other gotcha: some (actually, most) PC3200 and faster is spec'ed for 2.6 volts or higher. Some of Corsair's stuff is spec'ed for 2.75V. If you throw that into a mobo whose only option is vanilla 2.5 volts... good luck Instability, here we come.

So for a board that has no voltage adjustments, and can only do 2.5 volts, I would think about sticking with PC2700, which always seems to be spec'ed for 2.5 volts. Maybe that's a little conservative, what do you guys think?

Well, the new PC3200 is rated at 2.6V or 2.7V for 2-2-2 or 2-3-2 or 2-3-3 operation at PC3200 speeds. It should to PC2700 (and most certainly PC2100) at stock 2.5V.


Shuomaru - pretty much all PC2700 and PC3200 memory should work fine in that motherboard since PC2700 and PC3200 are official RAM specs (PC3200 just becoming 'official' recently but it was always an extension of the standard).

'Unofficial' RAM speeds (PC3500 and beyond, most notably PC4000 and up) might not work, because those RAM chips are designed to run at terrible RAM timings (3-3-3-8 or 4-4-4-8), and often doesn't run at the lower 'standard' RAM timings of 2.5-3-3, 2.5-2-2, 2-2-2, etc .


The short and skinny: buy pretty much any PC2700 or PC3200 sticks and you should be fine (just make sure it is Regular DDR: unbuffered and non ECC). Don't buy PC3500 or above because they run at nonstandard timings (which is fine because that RAM is more epensive anyway).

 

[mechBgon]

My view partly comes from seeing my A7N266-VM/AA, one of the most stable motherboards EVAR, go unstable with a stick of my Corsair XMS3200C2 in it (at PC2100 speed, 2.5V). The Corsair is flawless to this day with 2.6-2.7 volts, I'm still using it now.

 

[BonzaiDuck]

'Unofficial' RAM speeds (PC3500 and beyond, most notably PC4000 and up) might not work, because those RAM chips are designed to run at terrible RAM timings (3-3-3-8 or 4-4-4-8), and often doesn't run at the lower 'standard' RAM timings of 2.5-3-3, 2.5-2-2, 2-2-2, etc .

______________________________

I've been having a p------g contest with a friend who runs low-latency Mushkin PC3500's. He was singing songs of praise for the settings he gets with those modules at speeds between 200 external frequency and 216 -- 2, 2, 2, 5. But I was able to set timings for my PC4000's to 2.5, 4, 4, 5; 2.5, 4, 3, 5; and 2.5, 3, 3, 6. All these provided flawless MEMTEST86 results through ten iterations or more.

I suppose the Mushkins are better for stock FSB speed, so you have to be committed to running a faster FSB to take advantage of "unofficial" memory speeds with the looser latencies, and some "looser latencies" are worse than others: several manufactures are shipped with SPD values of 3, 4, 4, 8.

For another machine, I found some nifty PC2700's in a 512 or 1 GB kit for dual channel that ran at their spec at 2, 2, 2, 5. Not sure, but I think the manufacturer was "PQI" or something . . . Some might find them pricey -- I think a 2x256 kit was around $110 in July, '04.

 

[jiffylube1024]

Originally posted by: BonzaiDuck
'Unofficial' RAM speeds (PC3500 and beyond, most notably PC4000 and up) might not work, because those RAM chips are designed to run at terrible RAM timings (3-3-3-8 or 4-4-4-8), and often doesn't run at the lower 'standard' RAM timings of 2.5-3-3, 2.5-2-2, 2-2-2, etc .

______________________________

I've been having a p------g contest with a friend who runs low-latency Mushkin PC3500's. He was singing songs of praise for the settings he gets with those modules at speeds between 200 external frequency and 216 -- 2, 2, 2, 5. But I was able to set timings for my PC4000's to 2.5, 4, 4, 5; 2.5, 4, 3, 5; and 2.5, 3, 3, 6. All these provided flawless MEMTEST86 results through ten iterations or more.

I suppose the Mushkins are better for stock FSB speed, so you have to be committed to running a faster FSB to take advantage of "unofficial" memory speeds with the looser latencies, and some "looser latencies" are worse than others: several manufactures are shipped with SPD values of 3, 4, 4, 8.

For another machine, I found some nifty PC2700's in a 512 or 1 GB kit for dual channel that ran at their spec at 2, 2, 2, 5. Not sure, but I think the manufacturer was "PQI" or something . . . Some might find them pricey -- I think a 2x256 kit was around $110 in July, '04.

The PC3500 Muskins used to be overclocked PC3200 memory (ie the famous BH-5 chips, which could run at 2-2-2-5 at 220 MHz DDR and above with extremely high voltages) and now they use, I believe Samsung TCCD chips, just like those PQI sticks you were talking about.

Almost every company's 2-2-2-5 chips now use Samsung's revision TCCD chips, although Crucial Ballistix 2-2-2-5 memory is different - they use the new Micron rev. "G" chips.

So, yeah, his Mushkin PC3500 sticks would work fine in your board at any timings too, but that's some damn expensive RAM to run at PC2100 at!!!

All PC4000 has bad timings because, as said, it's not an official speed so they do not have to run at good timings.

New 2-2-2-5 PC3200 memory is usuall rated at 4.0ns or 4.1ns, which is 250 MHz, but remember RAM doesn't have to run at it's rated speed, just at what they sell the chips at (this is why, with relaxed timings, most 2-2-2-5 PC3200 will hit 250 MHz, but not all).