BUS speeds and DDR

[athlonxp2000]

hi everyone,

i was wondering if someone can explain a little about bus speeds and ddr to me for the p4. for AMD, thanks to the ppl from this forum, i've gained a basic understanding of how it works. seems pretty straight forward. for 133 fsb cpus:

133 FSB * 2 = 266DDR

or for 166 cpus:
166 FSB * 2 = 333DDR.

but how does it work for the pentium when they have 133 FSB * 4 = 533???? i don't get what type of memory i'm supposed to get so that it 'matches'... or or uses up all the bus/bandwidth or whatever. any type of help or explanation here? Thanks.

 

[AndyHui]

With the Pentium 4, you need to disassociate the FSB and the Memory speed.

The FSB (chipset to processor) is quad pumped, so at 133MHz, it is running at the equivalent of 533MHz.

Now for the RAM (chipset to RAM) bit. If you have a single channel DDR266, then you get 266MHz (obviously). Add in a 2nd RAM channel, 2 x 266MHz = 533.

There you go.

 

[thorin]

Andy got it pretty well. DDR = Double Data Rate (as you know). SDR = Single Data Rate. With SDR data is transfered only on the rising edge of the clock (SIN wave). With DDR Data is transfered on both the rising and falling edges of the click (SIN wave). With a Quad pumped bus the width of the data channel is doubled (16bits to 32bits or 8bits to 16bits or simple 2x8bits [dual channel] or 2x16bits ..... I don't remember the current actual bit widths) and data is transfered on both the rising and falling edges of the clock.

Thorin

 

[V00DOO]

I am currently running 512MB PC2100 on my Dell 4550 P4 2.53GHZ. Will I notice the speed difference if I replace 512MB PC2100 with 512MB PC2700. It's worth the upgrade?

 

[AgaBoogaBoo]

You may if you get PC3200, but not in everyday use. You probably will in gaming scores depending on your video card.

 

[athlonxp2000]

ok i understand how it works for a dual channel situation..."if you can't increase the clock speed, increase the bandwidth"

so 533 fsb = DDR266 * 2

but how bout for non-dual channel? what type of ram do i use to maximize the bandwidth/bus or whatever to take the full advantage of the 533?

and also how come he want really notice a big dif in every day use? if he uses PC3200... isn't he effectively using 3.2GB/s transfer rate?? where as for PC2100, he's only using 2.1?

 

[AgaBoogaBoo]

Originally posted by: athlonxp2000
ok i understand how it works for a dual channel situation..."if you can't increase the clock speed, increase the bandwidth"

so 533 fsb = DDR266 * 2

but how bout for non-dual channel? what type of ram do i use to maximize the bandwidth/bus or whatever to take the full advantage of the 533?

and also how come he want really notice a big dif in every day use? if he uses PC3200... isn't he effectively using 3.2GB/s transfer rate?? where as for PC2100, he's only using 2.1?

To get the 533mhz bandwidth in single channel, you have to use PC1066 RDRAM. This is the only way other than DC DDR RAM.

In everday use like Internet Explorer, E-mail, and a few other small applications, memory bandwidth isn't really a bottleneck. Because I'm sure IE doesn't need 2.1gbps of bandwidth, nor would Outlook. What they are bottlenecked by is hard drive speed and RAM in most cases, but in some others, clock speed of the CPU.

Once you get to 3D Applications and graphic intensive things, that is when more memory bandwidth helps.

 

[athlonxp2000]

To get the 533mhz bandwidth in single channel, you have to use PC1066 RDRAM. This is the only way other than DC DDR RAM.

In everday use like Internet Explorer, E-mail, and a few other small applications, memory bandwidth isn't really a bottleneck. Because I'm sure IE doesn't need 2.1gbps of bandwidth, nor would Outlook. What they are bottlenecked by is hard drive speed and RAM in most cases, but in some others, clock speed of the CPU.

Once you get to 3D Applications and graphic intensive things, that is when more memory bandwidth helps.

can you explain to me how that PC1066 works? i thought the 'PC' stands for how much the memory bandwidth is... isn't PC1066 just 1.066GB/s bandwidth?

so from what you're saying, most normal applications don't need more than DDR266??

 

[AndyHui]

DDR266 = PC2100 = 2.1GB/s bandwidth.

PC1066 RDRAM sends twice on each clock and is dual channel (because 16-bit RDRAM MUST be in pairs), and so total bandwidth = 4.2GB/s.

 

[howdyduty]

Nice facts FAQ Man. Short, sweet, and exacting. Thanks.

 

[thorin]

Originally posted by: V00DOO
I am currently running 512MB PC2100 on my Dell 4550 P4 2.53GHZ. Will I notice the speed difference if I replace 512MB PC2100 with 512MB PC2700. It's worth the upgrade?

Only if you're somehow going to change your bus speed from 266 to 333.

Originally posted by: AgaBooga

You may if you get PC3200, but not in everyday use. You probably will in gaming scores depending on your video card.

How do you figure that? If he's only running a CPU on a 266MHz bus how is ram rated for a 400MHz bus (which he'll still run @ 266MHz) going to help him?

Thorin