FSB on the MBP 17 = 800mhz.. so why the 667 ram?

Eluzion

macrumors 6502
Aug 7, 2007
328
0
Based on what I was told, the Santa Rose core doesn't run RAM at 800mhz frequency. The 800mhz advertised is the FSB, which is the northbridge connector with the CPU. So running DDR2 6400 RAM, it would still underclock to 667mhz.
 

Eidorian

macrumors Penryn
Mar 23, 2005
29,085
288
Indianapolis
Based on what I was told, the Santa Rose core doesn't run RAM at 800mhz frequency. The 800mhz advertised is the FSB, which is the northbridge connector with the CPU. So running DDR2 6400 RAM, it would still underclock to 667mhz.
That's right! :D
 

Eluzion

macrumors 6502
Aug 7, 2007
328
0
Must be a mobile CPU thing though because every CPU (AMD or Intel) I've used on a desktop runs a 1:1 ratio with the FSB. Either way, no biggy. MBP is still a beast. ;)
 

Mindflux

macrumors 68000
Oct 20, 2007
1,989
1
Austin
Must be a mobile CPU thing though because every CPU (AMD or Intel) I've used on a desktop runs a 1:1 ratio with the FSB. Either way, no biggy. MBP is still a beast. ;)

You must not have been around a lot of desktops.

I have a slew of 1200 Athlon's at the office that run at a 133Mhz multiplier for CPU clock frequency. The ram? DDR-2100 (266MHz)
 

Eidorian

macrumors Penryn
Mar 23, 2005
29,085
288
Indianapolis
You must not have been around a lot of desktops.

I have a slew of 1200 Athlon's at the office that run at a 133Mhz multiplier for CPU clock frequency. The ram? DDR-2100 (266MHz)
133 MHz double pumped = 266 MHz

Not in actual clock speed though. The RAM still runs at 133 MHz.
 

Eidorian

macrumors Penryn
Mar 23, 2005
29,085
288
Indianapolis
That and more and more of the Intel chips that have the shiny new 1333MHz FSBs can run on 800MHz or faster DDR2 (though I think that the actually, the 1333 is DDR3 RAM... but whatever)
Yeah just thinking about it does give headaches when you now add DDR3 into the mix.

DDR = Memory Clock * 2 (133 MHz = DDR-266 = PC 2100)
DDR2 = Memory Clock * 4 (133 MHz = DDR2-533 = PC2 4200)
DDR3 = Memory Clock * 8 (133 MHz = DDR3-1066 = PC3 8500)

The 1,333 MHz front side bus would be 333 MHz * 4. (quad pumped)
 
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