DRAM Almost as Fast as SRAM

An anonymous reader writes "IBM said it has been able to speed up the DRAM to the point where it's nearly as fast as SRAM, and that the result is a type of memory known as embedded DRAM, or eDRAM, that helps boost the performance of chips with multiple core calculating engines and is particularly suited for enabling the movement of graphics in gaming and other multimedia applications. DRAM will also continue to be used off the chip."

Re:What's the point?

[physicsboy500]

I'm sure it's not far off... after all they've already made a DRAM hard drive [tomshardware.com]

Re:What's the point?

[tomstdenis]

Because your spinning magnetic platter is a cheaper storage "solution" than edram, flash, whatever.

Unless you want to pay $25 per GB [again...], I'd wait until things improve.

And it isn't like they're not working on smaller/faster memory. Two years ago a 1GB flash was 99$ [in Canada], now they're ~40$ and you can get a 2GB flash for about the price of the 1GB. I imagine this year we'll see 4GB flash drives become more of a norm, and so on.

Most likely, ten years from now 80GB flash drives will be common place enough and not super expensive. But until then, spinning platers!

Re:xbox360

[Anonymous Coward]

eDRAM is used in many game consoles, including Sony PS2 and PlayStation Portable, Nintendo Wii and GameCube, and Microsoft Xbox 360

Source: eDRAM [wikipedia.org]

Most of them being IBM processors, and one MIPS. The news is not the development of eDRAM, but that IBM seems to be eager to replace SRAM with it in their processors.

Here's a better explanation

[Wesley Felter]

EE Times article. [eetimes.com] Today SRAM is used for processor caches, but new multicore chips need massive (i.e. expensive) cache. Because eDRAM is much denser than SRAM, it allows chip designers to fit much more cache in the same size chip, increasing overall performance. IBM and AMD use silicon-on-insulator (SOI) technology, while the rest of the industry uses bulk CMOS; eDRAM for bulk has been available for a while (it's used in Xbox 360 and BlueGene/L for example), but now IBM has developed SOI eDRAM that can be used in IBM's future processors (and maybe AMD's).

Re:To those wondering

[TheRaven64]

To add to this:

Cache misses are expensive. Really expensive. There are two ways of getting around this:

1. More hardware contexts so that you can switch to another thread instantly when a cache miss happens.
2. More (SRAM) cache.

The first one is better if you have highly parallel software, but isn't so good for single-threaded applications. The second is the more common approach. While SRAM uses six transistors per bit, DRAM uses one transistor and one capacitor. This could give something around three times the density, allowing CPU manufacturers to triple the amount of cache without increasing die size. Bigger cache means fewer cache misses, which means less time spent doing nothing.

For reference, a cache miss typically costs something around 1-200 cycles.

Re:eDRAM is quite old

[stevesliva]

Some big examples? PS2, Nintendo Gamecube, Wii, Xbox 360. All these consoles use eDRAM for their GPU's on-chip framebuffers to enhance their performance, and that goes back to at least the year 2000 when the PS2 came out.

Some will be quick to say "no, the Nintendo consoles use 1T-SRAM, not DRAM". Yeah, right, but even 1T-SRAM (despite its name) is a form of embedded-DRAM.

First, it is news because IBM is announcing that the performance is on par with SRAM, and because they have integrated their deep-trench eDRAM process with the SOI process used for their Power CPUs. The result? 3x the cache on the die. IBM has offered embedded DRAM with bulk technologies for a few generations, but this is the first real SOI annoucement.

Second, the consoles that have issued PR about using "embedded DRAM" with their GPUs don't actually embed DRAM on the GPU die. The "embedded DRAM" is a process offered by NEC that is separate from the Sony and TSMC processes used to fab the GPUs that supposedly have "embedded DRAM." I am pretty sure that all of the consoles you mention include a separate custom DRAM chip in the same package as the GPU. I am certain this is the case for the XBox 360 [arstechnica.com]. I am unsure about Sony. That DRAM process substantially modifies the back end wiring to make room for a MIM cap between the FETs and the first level of metal.

Re:What's the point?

[maxume]

Prices too high, sizes too small:

http://www.newegg.com/Product/Product.asp?Item=N82 E16820163159 [newegg.com]
http://www.newegg.com/Product/Product.asp?Item=N82 E16820220156 [newegg.com]
http://www.newegg.com/Product/ProductList.asp?N=20 03240522+1309421175&Submit=ENE&SubCategory=522 [newegg.com]

4GB flash for $40-$60, sd for $45, so $10-$15 per GB, right now. 1 GB cost $60 about 18 months ago(they are less than $15 now); extrapolate linearly, thats 64GB for cheap($60!) in 6 years, and 128+ in 8 years. That doesn't account for a slight depression in prices as the size of the chips used goes up.

I'd pay $100 extra for a laptop with a 32GB flash drive to go with the giant hard disk, just to save power. That's fairly likely in less than 4 years.

On Striping Raptors (10k rpm SATA drives)

[Anonymous Coward]

Note that striping (RAID-0) gives no benefit at all for writes, and destroys *latency* for reads. So it's only beneficial for streaming large files (say, in video editing) -- and of course it doubles your risk of data loss (as one failing drive zaps *all* your data) so it's really only useful for a work/scratch space for your large video/audio/CAD files.

Better to have a single 10K Rappy (or better a piece of 15K SCSI/SAS goodness -- where are 15K SATA drives already???) as a "system/apps/work cache" and then large 7K SATA drives for RAID-0 "scratch" pair and a RAID-1 "save" pair and even then burn all the important stuff to DVD weekly...

Of course the "more FPS!!!oneone" kiddies will ignore this advice and add blue case bottom lights too ;-)

Other upcoming types of RAM: Z-RAM and TTRAM

[thue]

I am in no way an expert, but I read about other upcoming types of RAM which also sound interesting:

Z-RAM. One cell is a single transistor. Faster than SRAM, which uses 6 transistors per cell. http://en.wikipedia.org/wiki/ZRAM [wikipedia.org]

TTRAM. One cell contains 2 transistors. As fast as SRAM, according to Wikipedia. http://en.wikipedia.org/wiki/TTRAM [wikipedia.org]

Re:Yes, trust IBM.

[Anonymous Coward]

Last time I checked, no one has died from an inability to afford faster RAM