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Hi everyones...thanks to read.
Two basic questions i could not get an answer after 1 hour of checking old posts: 1- Since most Pentiums 4 CPUs sold are with a 800MHZ FSB, it is correct to assume that the ram will always be a bottleneck unless i use the newer 800MHz DDR module? 2- If i use two 667MHz matched pair modules in dual channel, will the ram fsb will still be a bottleneck compared to the 800MHz cpu fsb? TIA for your reply. -- Alain(alias:Kilowatt) Montréal Québec PS: 1000 excuses for grammatical errors or omissions, i'm a "pure" french canadian! :-) (If replying also by e-mail, remove "no spam" from the adress.) |
#2
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Bottlenecks aside, the 800 MHz is actually a quad pumped 200 MHz. So
for synchronicity using an equally fast RAM is recommended. The 667 is a quadpumped 166 MHz. There would be some inefficiencies. Another issue that you should look into is the bus width. Compare the RAM and FSB bus widths. What really needs comparison is the total data that can be sent by the RAM, and the total data than can be passed through the Bus. Choose a configuration that optimises this. Getting RAMs that exceed the FSBs capability would be a waste as would be the converse. |
#3
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![]() KILOWATT wrote: Hi everyones...thanks to read. Two basic questions i could not get an answer after 1 hour of checking old posts: 1- Since most Pentiums 4 CPUs sold are with a 800MHZ FSB, it is correct to assume that the ram will always be a bottleneck unless i use the newer 800MHz DDR module? I don't think so. p4s use QDR (Quad data rate) to come up with the true FSB rating. Their real FSB rating on a "800" MHZ chip would be 200MHZ. if it took DDR it would be DDR 400 (pc3200). There is no such thing as QDR SDRAM, at the moment. Not on the Commercial PC market anyhow. There IS QDR SRAM, however. 2- If i use two 667MHz matched pair modules in dual channel, will the ram fsb will still be a bottleneck compared to the 800MHz cpu fsb? See above. There is often a performance boost for Dual channel, BUT.... TIA for your reply. -- Alain(alias:Kilowatt) Montréal Québec PS: 1000 excuses for grammatical errors or omissions, i'm a "pure" french canadian! :-) (If replying also by e-mail, remove "no spam" from the adress.) |
#4
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In article , "KILOWATT"
wrote: Hi everyones...thanks to read. Two basic questions i could not get an answer after 1 hour of checking old posts: 1- Since most Pentiums 4 CPUs sold are with a 800MHZ FSB, it is correct to assume that the ram will always be a bottleneck unless i use the newer 800MHz DDR module? 2- If i use two 667MHz matched pair modules in dual channel, will the ram fsb will still be a bottleneck compared to the 800MHz cpu fsb? TIA for your reply. -- Alain(alias:Kilowatt) Montréal Québec PS: 1000 excuses for grammatical errors or omissions, i'm a "pure" french canadian! :-) (If replying also by e-mail, remove "no spam" from the adress.) Don't forget that dual channel is 128 bits wide, and the CPU bus is 64 bits wide. On a DDR based system, a FSB800 processor was perfectly balanced with two DDR400 DIMMs in dual channel mode. (I.e. 6400MB/sec FSB is equal to two 3200MB/sec DIMMs). If you look at the results here with a Netburst processor, there is hardly any incentive to spend as much on memory as you spent on the processor. Anything at or over DDR2-533 is enough. If you used DDR2-800, the memory subsystem to FSB800 bandwidth ratio would be 2:1, meaning the burst of read data is being buffered in the Northbridge. http://www.anandtech.com/memory/showdoc.aspx?i=2732&p=4 Paul |
#5
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Thanks a lot for all your replies. Sorry for my very late reply.
From what i've read during the last few days... it seems that the memory bandwidth must be close as possible as the CPU bandwidth. 6400 megabits/sec is the theorical bandwidth of a 800MHz fsb cpu as is the one from a 800MHz ddr2 module. I wish to buy the p5ld2 motherboard from ASUS, wich have a 800 MHz fsb. It only supports 667MHz ddr2 modules, nonetheless. But with dual channel modules wich is supposed to give a 10% increase in bandwidth... i suppose that the memory bandwidth will closely meet the one from the cpu. |
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