A question of definition...

[Oda]

SDRAM = Synchronous Dynamic Random Access Memory right?

I was reading about the i815 being able to have the fsb and memory clock running at different speeds (ie 66/133 with a Celery and PC133 ram). SDRAM was launched to be running at the same clock as the fsb (66, 100, 133 for Klamath, Deschutes and CoppermineEB respectively, plus their AMD/Cyrix counterparts).

So what is the memory syncing with now, assuming it is syncing to something. Maybe SDRAM doesn't mean anything anymore?

 

[da loser]

well the i815 uses intel's new accelerated hub architecture
http://www.anandtech.com/showimage.html?u=/reviews/chipsets/intel/815/blockdiag.gif
"These boards can operate Front Side Bus and the memory clock asynchronously" from tomshardware http://www.tomshardware.com/mainboard/00q3/000706/i815-01.html
so they just have different clocks now

 

[Ulysses]

I guess 'synchronized' just means synchronized, but not necessaarily running at the same speed.

Here's one definition:

Synchronous DRAM (SDRAM) is a generic name for various kinds of DRAM that are synchronized with the clock speed that the microprocessor is optimized for. This tends to increase the number of instructions that the processor can perform in a given time. The speed of SDRAM is rated in MHz rather than in nanoseconds (ns). This makes it easier to compare the bus speed and the RAM chip speed. You can convert the RAM clock speed to nanoseconds by dividing the chip speed into 1 billion ns (which is one second). For example, an 83 MHz RAM would be equivalent to 12 ns.

 

[Goi]

The synchronous in SDRAM simply means its signal is driven via some clock edge. This clock can be any clock. When SDRAM first came out, its memory clock is tied to the FSB. Nowadays, the FSB and memory have separate clocks and are independent of each other. So, even though SDRAM may not be synchronous to the FSB, its still synchronous to its own memory clock running at an independent clock speed.

 

[Oda]

Thanks for the replies.



<< Its still synchronous to its own memory clock running at an independent clock speed. >>



This seems to sum up the responses, but I am not very convinced. Of course it has to be synchronous to itself!

Ah well...

 

[Goi]

Yes, its synchronous to its own memory clock, which is why its called synchronous DRAM(SDRAM).
Before SDRAM, DRAM types such as normal DRAM, FPM-DRAM, EDO-DRAM, BEDO-DRAM, etc aren't synchronous to any clock at all, because they had no clock. They aren't clock driven at all, which is why their access time/speed is measured in ns rather than MHz.

 

[Oda]

Ah thanks Goi. There's the explanation which I wanted.