Why does 800 mhz RAM require a 1600 mhz FSB?
Bookmark this page:
 Yahoo!
 Google
 Windows Live
 del.icio.us
 digg
 Netscape
|
|
||||||||||||||||||||||
|
Posted by Peter Olcott on May 15, 2008, 7:33 am
Please log in for more thread options http://www.dell.com/content/products/productdetails.aspx/precn_t7400?c=us&cs=04&l=en&s=bsd Speed 667MHz and 800MHz fully buffered ECC DIMMs Note: 800MHz memory requires 1600MHz FSB processor Aren't the front side bus and memory speed supposed to be matched? | ||||||||||||||||||||||
|
Posted by Dave on May 15, 2008, 9:00 am
Please log in for more thread options >
> Speed 667MHz and 800MHz fully buffered ECC DIMMs > Note: 800MHz memory requires 1600MHz FSB processor > > Aren't the front side bus and memory speed supposed to be matched? > > That is a persistent and totally untrue rumor which just refuses to die. Computers haven't had a single clock speed in so long that I can't even remember when that stopped being the case. But it was a loooooooonnnnnnnnngggggggggg time ago (decades?). In general, the motherboard chipset determines what RAM is supported, and the RAM has NO RELATION at all to the installed CPU. However, certain CPUs have memory controllers built into them. I don't know about the Xeon like in the link you listed. It's possible that the Xeon has a memory controller. That might explain why it says 800MHz memory requires 1600MHz FSB processor. That would make sense, as it would simply divide the clock speed by two to run the RAM. But obviously, even if you have a 1600MHz FSB processor with 800MHz RAM, the CPU and RAM are not matched. So even in THIS case, you don't need to match RAM to FSB. -Dave | ||||||||||||||||||||||
|
Posted by kony on May 15, 2008, 9:14 am
Please log in for more thread options On Thu, 15 May 2008 06:33:00 -0500, "Peter Olcott"
>
http://www.dell.com/content/products/productdetails.aspx/precn_t7400?c=us&cs=04&l=en&s=bsd
>
> Speed 667MHz and 800MHz fully buffered ECC DIMMs > Note: 800MHz memory requires 1600MHz FSB processor > > Aren't the front side bus and memory speed supposed to >be matched? > Often they are matched, but often modern chipsets can run asynchronous clock rates for the two and then use a divider to determine the ratio like 1:1, 1:1.2, 1:1.25, 1:1.5 (FSB:Memory) However, in this case they are "matched", they just used the wrong terms in explaining it. 800MHz in DDR2 terms really means 400MHz bus clock x 2 (2 as-in DOUBLE data rate memory) = 800 1600MHz in FSB terms really means 400MHz bus clock x 4 (4 as-in quad pumped data rate) = 1600 So you do actually have synchronous clock rates in this case, 400:400 or 1:1. | ||||||||||||||||||||||
|
Posted by Gumby on May 15, 2008, 10:03 am
Please log in for more thread options
> Often they are matched, but often modern chipsets can run
> asynchronous clock rates for the two and then use a divider > to determine the ratio like 1:1, 1:1.2, 1:1.25, 1:1.5 > (FSB:Memory) > > > However, in this case they are "matched", they just used the > wrong terms in explaining it. > > 800MHz in DDR2 terms really means 400MHz bus clock x 2 (2 > as-in DOUBLE data rate memory) = 800 > > 1600MHz in FSB terms really means 400MHz bus clock x 4 (4 > as-in quad pumped data rate) = 1600 > > So you do actually have synchronous clock rates in this > case, 400:400 or 1:1. > Yea, this is how it works but you can set any ram to any speed in the mb bios so there is no requirement that you have to have 800mhz ram. You just have to make sure you buy ram that can do 800mhz or better if you want the cpu and ram to run synchronously. | ||||||||||||||||||||||
|
Posted by kony on May 16, 2008, 1:19 am
Please log in for more thread options wrote:
>
>> Often they are matched, but often modern chipsets can run
>> asynchronous clock rates for the two and then use a divider >> to determine the ratio like 1:1, 1:1.2, 1:1.25, 1:1.5 >> (FSB:Memory) >> >> >> However, in this case they are "matched", they just used the >> wrong terms in explaining it. >> >> 800MHz in DDR2 terms really means 400MHz bus clock x 2 (2 >> as-in DOUBLE data rate memory) = 800 >> >> 1600MHz in FSB terms really means 400MHz bus clock x 4 (4 >> as-in quad pumped data rate) = 1600 >> >> So you do actually have synchronous clock rates in this >> case, 400:400 or 1:1. >> >
>Yea, this is how it works but you can set any ram to any speed in the mb >bios so there is no requirement that you have to have 800mhz ram. On many systems you can, but on that specific OEM workstation? I would not assume it, and one of the reasons for it's higher cost is it support more memory which may reduce the flexibility in choosing different combinations of speeds and timings (if again, they let you choose at all instead of it all being hidden and unsettable "auto" configured). >You just
>have to make sure you buy ram that can do 800mhz or better if you want the >cpu and ram to run synchronously. IMO, anyone should buy -800 memory or better anyway, the cost different is minor and if they can set speed and/or timings they may have the potential for a faster system as a result. | ||||||||||||||||||||||
| Similar Threads | Posted |
| Why does 800 mhz RAM require a 1600 mhz FSB? | May 15, 2008, 7:33 am |
| Dissipatore x xp 1600+ va bene sul 2500?! | October 18, 2005, 2:23 pm |
| Question about what UPS rating we require | June 27, 2006, 3:25 am |
>