What performance difference is there between PC2100 and PC2700 memory?

[JEDI]

I just picked up 1 gig worth of PC2100 (Officemax's free memory deal).

if a system required pc2700 memory, and i put in pc2100, how much slower would it be?

THX

 

[DieHardware]

PC2100 is rated to run @ 133MHz, PC2700 for 166MHz.

 

[TheCorm]

Well if you were going purely by memory bandwith then PC2700 has around 30% more bandwith than PC2100.

But in real life usage I would expect the performence difference to be far smaller if the memory is the only difference between the two systems.

 

[Pauli]

Look, memory by itself does not have a "speed" - it doesn't have a clock on it -- that's on the motherboard. The memory "speed" is the bus speed that it is rated for. That said, PC2100 is rated to run at speeds up to 133Mhz and PC2700 is rated to run at speeds up to 166Mhz. There is no difference in the "speed" of these two types of memory if they are installed into a system that is running a bus speed of 133Mhz -- the memory "speed" does not change if the bus speed is not changed.

To answer your question, I doubt that your system requires PC2700, unless you are overclocking your Front-Side Bus (FSB), because there aren't any mainstream processors that run on a 166Mhz bus (Intel at least, any AMDs? I don't know). So, if your system indeed requires PC2700 DDR SDRAM, then it just won't work at all, or have intermittent crashes, if you put PC2100 in it. However, if you are running a FSB of 133Mhz or less, then you shouldn't notice any performance difference at all, because you aren't actually changing the speed the system is running at. Most people buy PC2700 because they want to overclock their system beyond its 133Mhz FSB specification. BTW, I used 133Mhz and 166Mhz to describe the FSB setting, but since it's DDR SDRAM, the actual bus speed is doubled to either 266 or 333Mhz.

 

[DieHardware]

PC2100 is rated to run at speeds up to 133Mhz and PC2700 is rated to run at speeds up to 166Mhz.

Is there an echo in here?😉

However, if you are running a FSB of 133Mhz or less, then you shouldn't notice any performance difference at all, because you aren't actually changing the speed the system is running at. Most people buy PC2700 because they want to overclock their system beyond its 133Mhz FSB specification.

You can run RAM asynchronously(i.e. FSB@133MHz, RAM @166MHz), although the latency hit of DDR doesn't really offer much of an improvement when run this way.

I used 133Mhz and 166Mhz to describe the FSB setting, but since it's DDR SDRAM, the actual bus speed is doubled to either 266 or 333Mhz

No its not, bus/RAM speed remains the same, either 133/166MHz or because of the two hits per cycle 266/333 equivalent.

 

[Pauli]

Yeah, DieHardware, sorry to repeat what you said and not give you credit for it!

Also, yeah, you're right about the 133/166Mhz business, although the DDR logic allows it to do that leading edge/trailing edge stuff to allow the RAM speed to effectively double, even though it is still running at 133/166.

 

[pdragn78]

I'm not sure I really understand the difference between the PC2100 and PC2700, but maybe you guys can help me troubleshoot.

I bought 2 Dell 4550 computers: computer#1) P4, 2.4 Ghz, 533Mhz FSB computer#2)P4 2.0 Ghz, 400 Mhz FSB; I installed one stick of RAM into both computers, a 512MB PC2700.

Computer #1 in bios shows that the memory is running at 333MHz so its running fine, but Comptuer #2 only shows as 266 MHz; Both computers originally came with 128MB of PC2700 RAM, but computer #1 memory ran at 333MHz while computer #2 ran at 266MHz originally. I had thought that maybe computer #2 may have come with a pc2100 ram originally, but was suprised to find out (after opening the computer) that it was acutally pc2700 RAM. Even after removing the 128MB memory and replacing it with the new PC2700 ram computer #2 still reads at 266MHZ in bios.

So my question, did I waste my money on pc2700 ram when computer#2 highest speed is pc2100? I can't change the memory speed in bios it is part of the default i guess. Also why would Dell put in a 128MB stick of pc2700, when it only runs at 266MHZ...i'm kinda confused. Any help would be greatly appreciated.

 

[JZilla]

Originally posted by: pdragn78
I'm not sure I really understand the difference between the PC2100 and PC2700, but maybe you guys can help me troubleshoot.

I bought 2 Dell 4550 computers: computer#1) P4, 2.4 Ghz, 533Mhz FSB computer#2)P4 2.0 Ghz, 400 Mhz FSB; I installed one stick of RAM into both computers, a 512MB PC2700.

Computer #1 in bios shows that the memory is running at 333MHz so its running fine, but Comptuer #2 only shows as 266 MHz; Both computers originally came with 128MB of PC2700 RAM, but computer #1 memory ran at 333MHz while computer #2 ran at 266MHz originally. I had thought that maybe computer #2 may have come with a pc2100 ram originally, but was suprised to find out (after opening the computer) that it was acutally pc2700 RAM. Even after removing the 128MB memory and replacing it with the new PC2700 ram computer #2 still reads at 266MHZ in bios.

So my question, did I waste my money on pc2700 ram when computer#2 highest speed is pc2100? I can't change the memory speed in bios it is part of the default i guess. Also why would Dell put in a 128MB stick of pc2700, when it only runs at 266MHZ...i'm kinda confused. Any help would be greatly appreciated.

You would need at least a 2.4ghz cpu to use the 333mhz bus. Seeing as the price difference is so low it doesn't really matter and maybe you can use them in the future. I guess it's cheaper for Dell only to buy PC2700, instead of buying both PC2100 and PC2700.l

 

[Buk]

I'm playing with an AMD 1800 T'bred A on an Asus NF2 mobo trying to check memory speeds so I can offer the following information.

9.5 x 133fsb -> 3dmk2001se score of 8235
9.5 x 166fsb -> " " " 9295

This was run with the processor at the same speed as the memory so processor speed factors in, too.

Having said that, I'll tell you that with three sticks on PC2100 memory (Crucial, Kingston Valueram, and one with Hynix chips - all standard, non-high performance), at timings of 6, 3, 3, 2.5, they all run at 170+ fsb. So, there's a good chance that your pc2100 memory will run at pc2700, YMMV though.

Good luck................

 

[pdragn78]

Originally posted by: JZilla

You would need at least a 2.4ghz cpu to use the 333mhz bus. Seeing as the price difference is so low it doesn't really matter and maybe you can use them in the future. I guess it's cheaper for Dell only to buy PC2700, instead of buying both PC2100 and PC2700.l

Thanks for the advice...I agree its not worth returning the memory to save a few bucks; I'll leave it in there for now