DDR ram mixing me up!!

[afd00]

hi guys..

please help me get something straight (i never worked with DDR ram before):

i want to get a 256MB DDR ram chip for my motherboard whose manual says its memory modules can run on 100Mhz (system bus) or 266Mhz.

i checked out a website for models and prices of DDR and it listed 2 types: PC266 and PC2100 which we equally priced.

conclusion: i am confused!! do both work equally well on my system?? do the numbers 266 and 2100 correspond to the Mhz values on which the memory can operate?? if so why do they have similar prices and will the 2100 work as if it is a 266 because this is a motherboard limitation??

thanks in advance....

[$1500-P4 gamer]

266mhz and pc2100 is the same thing. Same speed. pc2100 is just the correct terminalogy for ddr mem that is 266mhz speed. Your mobo can run either 100mhz fsb or 133. In ddr that is 200 or 266mhz. 100mhz fsb (200ddr) would be for Athlons and durons. The Athlon XP is 266mhz ddr(133mhz fsb). Did that help ya?:t

[afd00]

yeah thanks - i think i'm fine now.

i also referred back to my motherboard's manual and saw that 2100 is the memory's bandwidth in MBytes/sec when operating at 133 Mhz fsb ie the DDR memory can transfer 2.1 GB of data per second when the fsb is running at 133,000,000 clock cycles per second

i even did the calculations and it makes sense if each cylcle 8 bytes are transferred:

8 bytes * 133,000,000 bus cycles/sec * 2 memory cyles/bus cylce (the case of DDR) = 2,128,000,000 bytes/second = 2,078,125 KBytes/sec = 2,029 MBytes/s (so the 2100 rating is somehow overestimated!!!!!!!!)

anyway, i just thought of sharing my results, and if someone has an explanation for the 8 bytes value i found please tell me. thanks!!

[Peter M]

Well simple, DIMM data bus is 64 bits wide (plus eight for ECC, but that's just redundancy data), so in every data transmission, you get eight bytes.

[$1500-P4 gamer]

Originally posted by afd00
yeah thanks - i think i'm fine now.

i also referred back to my motherboard's manual and saw that 2100 is the memory's bandwidth in MBytes/sec when operating at 133 Mhz fsb ie the DDR memory can transfer 2.1 GB of data per second when the fsb is running at 133,000,000 clock cycles per second

i even did the calculations and it makes sense if each cylcle 8 bytes are transferred:

8 bytes * 133,000,000 bus cycles/sec * 2 memory cyles/bus cylce (the case of DDR) = 2,128,000,000 bytes/second = 2,078,125 KBytes/sec = 2,029 MBytes/s (so the 2100 rating is somehow overestimated!!!!!!!!)

anyway, i just thought of sharing my results, and if someone has an explanation for the 8 bytes value i found please tell me. thanks!!
Got your answer right here. 8 bytes is one Dword.

[Peter M]

No :)

byte - 8 bits
word - 16 bits
dword - 32 bits (d for double)
qword - 64 bits (q for quad)

[$1500-P4 gamer]

opps sorry it would be one qword. 8bits in a byte. 8 bytes is 8x8=64 bits. qword is 64bits.