SDRAM vs DDR2 RAM?

I'm ashamed to say I forgot what the difference is between sdram and ddr2 ram. And whats the diff between ddr and ddr2 ram, newer generation ram sticks thats more efficient? /confused

Faced with an option of a notebook with 2gig SDRAM @ 800MHz, or 2gig DDR2 ram at 667MHz. Which is faster?

Jeez, been a while since I read that A+ certification book..got symmetrical and asymmentrical ram all mixed up in my head, lol

 

No SD-RAM Ever reaches 800MHZ,they are both DDR2.
(And with "that notebook" I think you mean *that* Zepto with 8600GT)

 

Yeap, both DDR2 there.

But for the record...

These are all synchronous DRAM, synchronous meaning it uses a clock to synchronize with an external bus.

DDR adds a second bit transmitted per cycle, one on the rise, one on the fall. It does this at the cost of latency. DDR2 theoretically doubles the speed again, this time by running the external bus at twice the speed of the memory cells. Again, this is at the cost of latency, which is why early DDR2 implementations (like 533mhz) were slower than the DDR alternative.

DDR3 is a lot less of a leap. It's mostly an improvement to power consumption with dual gate transistors and such, to allow higher clock speeds and lower voltages. It does offer some less major performance enhancements like an 8 bit prefetch (DDR2 offered 4 bit, DDR 2 bit). I'm not sure how much the larger prefetch will help without the other associated improvements from those generations. When DDR3 finds it's way into notebooks we should see a nice battery life improvement.

 

Thank you for the detailed explanation Eth.

Rather than make a new thread, I should just ask here real quick.

Front Side Bus..what exactly does that control and the advantage of having a faster front side bus speed is?

 

It's best if your FSB (front side bus) matches the speed of your RAM.

Think of it this way, you have a car that can run at 200 mph but the driver's skill is only good till 100 mph, he can easily crash beyond 100. Or the other way around, a skilled race car driver that only has a car that can go 100 mph at maximum.

It's best if they match. The bandwidth of the RAM has to match the bandwidth your CPU can accommodate.

 

Although that's not as true as in the past, with hypertransport interconnects these days. I'm really not sure of the interaction over a hypertransport bus.