Chips of today (like the A64) may soon be replaced by chips with onboard DRAM.
Though we've moved from one to multiple cores and to smaller and smaller die sizes, one thing has stayed constant - by and large, processors have functioned using the same intrinsic design. L2 cache, L1 cache, pipe. This basic technology has been with us ever since the CPU has been around, and though tweaks to the system have given us increases, the basic technology has stayed the same. Now, it appears
IBM will make the first real component change in a very long time - the SRAM normally found in the cache is being changed to DRAM.
The alteration is subtle, but its effects could be very potent. DRAM has a considerably lower transistor count than an equal amount of SRAM, taking up only 1/3 of the footprint. This will greatly reduce both energy usage and (subsequently) thermal output, especially in standby modes. In standby, the chip will use only 1/5 the current power draw, since so much less energy is required to keep the data stored in DRAM.
The change has been long overdue, but until now there wasn't the technology to lay the transistor arrangements out right on a chip die. As the die shrink race has continued, though, chip makers have been running out of options - SRAM is just too big. That size comes with another issue - transistor leakage and latency issues are beginning to affect overall chip designs as everything else scales down.
DRAM will allow a lot more cache, which (though slightly slower) will provide some excellent buffering for larger graphics files like games as well as multi-tasking. According to IBM, the change is already in place for the move to 45nm, and we can expect to start seeing it appear in the company's processors starting in 2008.
Could we be seeing IBM come back strong into the consumer chip market? Only time will tell. In the meantime, leave us your thoughts on DRAM-on-die
in our forums.
19 Comments
Discuss in the forums Replyi guess DRAM has gotten to the point where the speed difference isn't huge enough to warrant sticking with the (much more expensive) SRAM.
Most BIOS will run a diagnostic on the processor's cache, if you look at the POST screen you will see one of the first entries wiil read 'xxxx SRAM' where x is the amount of cache in kB. At least on motherboards for the K8...
ATi's Xenos GPU in the XBox360 has a DRAM on the same package, but not enmbeded on the chip.
SRAM has been used for a long time for a reason, its fast, its easy to connect in circuits
I would have thought it might make more sense to have like 256k L2 cache made of SRAM, and then a much larger L3 cache that can store much more, if its all on the processor the access time will be minimal anyway
PS Isn't computer Architecture fun boys and girls!?
Keep L2 cache the same size (MB) use the freed up space (mm²) for more SRAM L1 cache
Also at announcement date Fusion by AMD was to be the discrete GPU killer and then after some of the smarter geek sites pondered how it would work, ATI withdrew their replacement of discrete graphics to a much more sober laptop integrated graphics replacement. I believe this will happen to Dram for cache, it will find the same fate reduced to being designed for lower ends of the market where saving a dollar or two from the cost of a CPU is important.
If I am wrong and it turns out to be as nearly as fast and smaller in size per MB when compared to SRAM then AMD will be able to benefit since when they added the on-board memory controller they lost real Estate room and smaller memory might help them put an additional MB or two on a dual core CPU. That is a big if since, if this was so good Intel would have announced their work on this DRAM memory shrink since it seems that both companies announce almost similtaniously lately.