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Created On: 09/01/2004 04:01 PM
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 09/01/2004 04:01 PM
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Megadeth
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Hi! Folks, I got a question about the AMD Sempron 3100+. Does the processor have suport for PC3700 memory or PC4000?

Can DDR2 be used in any motherboard or is there a special motherboard that you need?
 09/01/2004 04:08 PM
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Silk_the_Absent1
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Yes and no. Yes, it can be used, bt no it won't run at those speeds. All Athlon64's have an on-die memory controller, but it is limited to PC3200, so you can use faster ram, but it will be underclocked down to PC3200 speed. Really the only time you'd ever use faster ram is if you were overclocking. The only other time you might want faster ram would be so you could underclock it to be able to use more aggressive timings.

DDR2 uses a different DIMM socket, for which there are no DDR2 chipsets for the A64 platform yet. And right now there is no point in running DDR2, as the timings on them suck, and the memory controller won't use the faster speeds.

-Adam
 09/01/2004 04:10 PM
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Megadeth
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So you mean there is no use in buying faster RAM than PC3200?
 09/01/2004 04:11 PM
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Silk_the_Absent1
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If you are overclocking the bus past 200 then yeah, you would want some faster memory, also if you got faster memory, you can underclock it to lower speeds and make the timings more aggressive.

-Adam
 09/01/2004 04:25 PM
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Megadeth
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Well, I thought that if a processor had 266 MHz, then it is compatible with PC2100 or higher.
 09/01/2004 04:34 PM
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Silk_the_Absent1
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LOL, I'm talking about the actual bus speed, for a 266bus, its real speed is 133, 166 for 333, 200 for 400. BTW, the bus on A64's is still 200, it's just using a multiplier, similar to the way Intel quad pumps their FSB's (100*4 for 400Mhz FSB, 133*4 for 533, 200*4 for 800).

So yes, it can use faster ram, but the controller won't let it run faster then 200 (400DDR), unless you are overclocking, then it will raise the ram speed along with the bus speed.

-Adam
 09/02/2004 02:36 AM
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Greyhound
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QUOTE Does the processor have suport for PC3700 memory or PC4000?
No processor or motherboard *officially* supports anything beyond PC3200/DDR400 memory for the simple reason that there is no official JEDEC-standard for anything faster than DDR(I)400/PC3200.

Since ALL DDR-SDRAM is fully backward-compatible, PC3700/PC4000/whatever memory would run just fine with your Sempron-system, BUT it will run at PC3200-speeds as long as you don't overclock.

That being said, it only makes sense to use anything faster than PC3200/DDR400 memory if you're definitely going to overclock at some point, if you don't plan to overclock you'd better spend the extra $$ on some low-latency PC3200 memory(e.g. Corsair XMS3200XL or something).
QUOTE Can DDR2 be used in any motherboard or is there a special motherboard that you need?
As far as modern AMD-platforms are concerned(i.e. Socket 754/939/940) the memory-controller is integrated into the processor, NOT the chipset.

Due to DDR-II's high cost and abysmal latencies(compared to modern DDR-I memory) even the fastest official standard(DDR-II 533/PC2-4200) does not offer any benefit whatsoever over good old DDR-I memory right now...AMD processors won't support DDR-II memory until there will be a noticable increase in performance over DDR-I and until prices become more affordable which probably won't happen before late next year or early to mid-2006.

Btw, like Adam already pointed out DDR-II memory uses 240-pin DIMMs while our plain old DDR-I memory uses 184-pin DIMMs, so a DDR-II stick wouldn't even mechanically fit in a DDR-I socket.
QUOTE Well, I thought that if a processor had 266 MHz, then it is compatible with PC2100 or higher.
Well, you're on a Socket 754-platform with your Sempron 3100+, so you got the same basic architecture as an Athlon 64 which means there is no 'FSB' in the classical sense anymore.

ALL Socket 754 processors have an on-die memory-controller which means the memory-controller is integrated directly into the CPU-core instead of being part of the chipsets' Northbridge.
This significantly reduces latencies when accessing memory as the memory has its own dedicated path directly connected to the processor – memory-accesses no longer have to go through an FSB(Frontside Bus, aka System Bus) like on a 'classical' platform.

Furthermore, the processor communicates with the chipset and thus the 'rest of the system'(excluding memory, of course! via a Hypertransport-link.

The memory-frequency is derived from the processors' core-clockspeed, NOT the HT-links' clock or the base-clock.

Base-clock(200MHz)---[core-clock multiplier]--->CPU core-clock---[memory divider]--->Memory-clock
I
I>[Hypertransport-multiplier]
I
Hypertransport-clock

Example for your processor(Sempron 3100+):

200MHz---[x9.0]--->1800MHz---[/9]--->200MHz(DDR400)
I
I>[x4.0]
I
800MHz(1600MHz effectively)

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