Computing.Net - DDR types

Subject: DDR types

Original Message

Name: sky42
Date: January 13, 2008 at 17:43:45 Pacific
Subject: DDR types
OS: Winxp
CPU/Ram: 2700/512
Model/Manufacturer: eMachines

Comment:

I have an assortment of DDR chips, some are PC2100 and some are PC2700. Are these chips interchangable on the same machine or are they typically specific to a given machine? What are the specifics that make them unique to a given machine, e.g. FSB speed, cpu type, BIOS, etc? Thanx

Report Offensive Message For Removal

Response Number 1

Name: OtheHill
Date: January 13, 2008 at 17:48:15 Pacific
Subject: DDR types

Reply: (edit)

http://en.wikipedia.org/wiki/DDR_SDRAM

Report Offensive Follow Up For Removal

Response Number 2

Name: jam
Date: January 13, 2008 at 17:48:49 Pacific
Subject: DDR types

Reply: (edit)

If you pair up different speed RAM sticks, they will be forced to run at the speed of the slowest. For example, if you were to install PC2100 + PC2700 in the same machine, they would run as if they were both PC2100.

Report Offensive Follow Up For Removal

Response Number 3

Name: aegis
Date: January 13, 2008 at 18:08:17 Pacific
Subject: DDR types

Reply: (edit)

pc2100 DDR266, core speed is 266mhz (max)
pc2700 DDR333. core speed is 333mhz (max)

Report Offensive Follow Up For Removal

Response Number 4

Name: sky42
Date: January 14, 2008 at 06:01:22 Pacific
Subject: DDR types

Reply: (edit)

Thanx for the good info. My last question is: will any DDR chip work in any machine calling specifically for DDR memory; and will any DDR2 chip work in any machine calling specifically for DDR2 memory?

Report Offensive Follow Up For Removal

Response Number 5

Name: OtheHill
Date: January 14, 2008 at 07:07:08 Pacific
Subject: DDR types

Reply: (edit)

Theoretically, yes. In the real world you can run into problems.

Report Offensive Follow Up For Removal

Response Number 6

Name: jam
Date: January 14, 2008 at 07:17:36 Pacific
Subject: DDR types

Reply: (edit)

The whole double data rate (DDR) & quad data rate (QDR) thing can get confusing...that's why I recommend reducing them to their actual frequencies, then you can compare "apples to apples". When you see DDR ratings such as DDR266, divide by 2 to get the actual frequency. And in the case of Intel CPUs (which use QDR), when you see the FSB such as 800MHz, divide by 4 to get the actual frequency. Then you can pair up the CPU with the correct RAM.
Just to clarify what aegis wrote:
"pc2100 DDR266, core speed is 266mhz (max)"
266MHz is the data rate speed...the actual frequency is 133MHz.
PC2700 (DDR333) runs at 166MHz freq.
PC3200 (DDR400) runs at 200MHz freq.
"will any DDR chip work in any machine calling specifically for DDR memory"
Theoretically, yes. But you should consider the CPU FSB & choose the RAM accordingly. If for example, you have a P4 that runs at 800MHz FSB (200MHz freq), you'll lose performance if you use PC2100 (133MHz freq) or PC2700 (166MHz freq)...PC3200 (200MHz freq) or better should be used in this case.
"will any DDR2 chip work in any machine calling specifically for DDR2 memory?"
Once again, yes...theoretically. Unfortunately, it's not that simple. In addition to what I wrote about pairing up the right CPU/RAM combo, you also have to look at the motherboard specs to see what RAM standard is supported. There can sometimes be issues relating to RAM density too.

Report Offensive Follow Up For Removal