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
Example for your processor(Sempron 3100+):
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