Posted by Graham Allan on January 13, 2014
Believe it or not, work the DDR4 standard was first started back in 2004. That’s now 10 years ago! Happy 10th birthday DDR4. 10 years ago Facebook was started up, there was no Twitter (2006), no iPhone (2007), and Google went public for $85/share (it is now $1,123/share). Even after those 10 years, you can’t go out a buy a computer with DDR4 in it. The JEDEC standard for DDR4 was published in September 2012 so why isn’t everyone using it? Why did it take so long?
That’s a long complicated story. Fundamentally, it’s just plain hard to make a single ended, wide parallel interface operate at the data rates envisioned for DDR4. Physics is getting in the way as the nanoseconds gave way to picoseconds and fewer and fewer of them. The traditional wide DDR SDRAM interface is running out of headroom and the system design compromises to enable such high speeds are getting expensive. It took a lot of bright engineers a long time to figure out what features are required in DDR4 to make it work in systems, and then agree on what was required, and then agree on how to tell other people what was required (e.g., write the standard). In my opinion, DDR4 is the most complicated DRAM standard transition since asynchronous DRAM gave way to the SDRAM in the mid-1990s (and that took 5 years from first work on the standard to computers shipping with it).
Also, for most PCs, laptops and embedded applications – DDR3 has been good enough when you consider price, latency, performance, etc. But, as it always is in the DRAM game, it’s mostly about price! Only servers crave DDR4 for the lower power the SDRAM offers and only servers are willing to pay for it. Higher data rates are nice but it’s the lower power that is most attractive. DDR4 is the first DRAM standard that does not target PCs and laptops for the first application market. Since DDR4 really targets servers first, that is a smaller segment of the DRAM market so the TAM for DDR4 is smaller than it was for DDR3 and will remain so until DDR4 ends up in laptops and PCs (both of which are declining markets themselves). That is a chicken and egg problem. Laptops and PCs will not embrace DDR4 until it becomes cheaper than DDR3 yet the shrinking TAM for DDR4 means the volume will not ramp very quickly and volume largely determines the price in the DRAM market.
So basically, there is nowhere for DDR4 to go yet and the future is only bright-ish.
Add to the complex equation that consumers are abandoning PCs and laptops for ultrabooks, tablets and smartphones which use lower power mobile SDRAMs such as LPDDR2 and LPDDR3. The volume for LPDDR2/3 is ramping up while the volume for DDR3 is waning. There is a lot more industry momentum around the mobile DRAMs (e.g., LPDDR2/3/4) than there is around the “PC” memories (e.g., DDR3/4) because the volumes are increasing and the prices are higher for mobile DRAMs. More of anything at a higher price is attractive if you sell that thing! However, nothing lasts forever and as the memory market volumes teeter towards mobile DRAMs and away from the PC DRAMs, I predict the prices of mobile DRAMs will fall, eventually to below the price per bit level of the PC DRAMs. This will likely happen within the next 2 years.
Finally, back to that DDR4 standard… For anyone who is familiar with the DDR4 standard, it does not define the 3200Mbps data rates that most articles about DDR4 talk about. How many times have you read that DDR4 is twice as fast as DDR3? That was true back when DDR3 was only standardized up to 1600Mbps. DDR3 has since been enhanced to accommodate data rates of up to 2133Mbps. The maximum speed for the current DDR4 standard is 2400Mbps (only 13% faster than the maximum speed for DDR3). In fact, 3200Mbps, once we get there, is only 50% faster than DDR3. There are also some other areas where the standard is not complete. JEDEC has been working diligently to update the standard – that cat was let out of the bag in a recent EEtimes article: http://www.eetimes.com/author.asp?section_id=36&doc_id=1320534&itc=eetimes_sitedefault&cid=NL_EET_Daily_20140103&elq=10ac88effa334363983119d0e84ed904&elqCampaignId=3302. One of those updates is likely to be for the speed grades above 2400Mbps.
DDR4 will have a future, but it will never be the DRAM “rock star” that DDR3 is. DDR3 has already been the king of DRAMs for longer than DDR2 was and it still has a long runway ahead of it. Long live the King!
Graham Allan is the Sr. Product Marketing Manager for DDR PHYs at Synopsys. Graham graduated from Carleton University's Electrical Engineering program with a passion for electronics that landed him in the field of DRAM design at Mosaid in Ottawa, Canada. Beginning at the 64Kb capacity, Graham worked on DRAM designs through to the 256Mb generation. Starting in 1992, Graham was a key contributor to the JEDEC standards for SDRAM, DDR SDRAM and DDR3 SDRAM. Graham holds over 20 patents in the field of DRAM and memory design.