JEDEC Reveals Key Aspects of DDR4
by Kristian Vättö on August 23, 2011 2:01 PM ESTDDR3 made its debut in mid-2007 when Intel released P35 chipset with support for DDR3. Today nearly all desktop, mobile and server platforms support DDR3. iSuppli estimates that DDR3 will account for roughly 90% of DRAM sales this year. However, the next generation DRAM technology is already just around the corner and JEDEC is scheduled to release the full DDR4 specification next year. Yesterday, JEDEC published some of the specifications of the upcoming DDR4 technology.
First and foremost, DDR4 will concentrate on performance and power consumption. The latter is achieved by lowering the voltage to 1.2V, compared to DDR3's 1.5V (although there are DDR3 modules with lower or higher voltage but 1.5V is the standard for most). The performance gain is achieved by increasing the frequency and DDR4 will start from 1600MHz. It's likely that we will see 1866MHz or 2133MHz modules as the standard though, considering that DDR3 went straight for 1066MHz as well, even though a 800MHz specification existed too. The projected maximum speed for DDR4 is 3200MHz but then again, DDR3's maximum is 1600MHz, yet 2133MHz DDR3 modules are available. We will likely see even higher bandwidth DDR4 modules in the future. JEDEC lists the prefetch buffer for DDR4 as 8n, which is identical to DDR3. If this ends up being the case the bulk of the performance increase will be due to higher operating frequencies enabled through more advanced signaling.
The higher operating frequencies come at the expense of some serialization of the interface. The SDRAM memory interface remains one of the last parallel buses in modern PCs. While it doesn't look like DDR4 will change that, we have heard reports of the new memory standard moving to a point-to-point protocol. In other words: one DDR4 module per memory channel. Note that JEDEC hasn't confirmed this will officially make it into the DDR4 spec.
Source: JEDEC
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gevorg - Tuesday, August 23, 2011 - link
What about CAS latencies? Are they going to increase like they did from DDR2 to DDR3?Kristian Vättö - Tuesday, August 23, 2011 - link
SemiAccurate is claiming CL12 as the standard for 2133MHz DDR4http://semiaccurate.com/2010/08/16/ddr4-not-expect...
DanNeely - Tuesday, August 23, 2011 - link
Yup. DDRN+1 is implemented primarily by doubling the bus speed and doubling the number of chips on a dimm accessed in parallel. SDR ram accessed on chip at a time. DDR1 2 chips, DDR2 4 chips, DDR3 8 chips, DDR4 will be 16 chips. I don't know if this will mean the end of 8 chip modules (especially in lower capacities), or if they'll start making chips that are functionally equivalent to dual core designs with 2 IO channels instead of only one.FaaR - Wednesday, August 24, 2011 - link
Dan, you're very confused.All current PC RAM (and all past too, except DRDRAM) is accessed in parallel: all chips in one bank (one side of the DIMM) make up the full width of the data bus.
Only DRDRAM accessed memory one chip at a time, because it was a serial setup.
fhaddad78 - Tuesday, August 23, 2011 - link
I'm not a hardware guru or anything and a lot of this stuff is over my head, but I kind of understand why memory architecture needs to change as processors become faster. I know there is a relationship and that is why for example Intel Core series cpus use DDR and why we don't see much benefit from memory speeds beyond DDR3 18xx. Ok, i'm rambling here...As the subject reads: DDR5
I noticed that AMD GPUs use DDR5 and my question is why do CPUs not use DDR5 yet? Is that memory different than the DDR3 memory used in today's cpus?
Thanks for sharing some insight into this mysterious and explainable phenomenon regarding memory specifications.
fhaddad78 - Tuesday, August 23, 2011 - link
No edit button...... cpus use DDR and ...
Should read:
... cpus use DDR3 and ...
LordanSS - Tuesday, August 23, 2011 - link
AMD (and nVidia's GPUs) use GDDR5, not DDR5. It's a completely different beast, heh. =)fhaddad78 - Tuesday, August 23, 2011 - link
Ah. This definitely has an affect on my question. (:cosmoanu87 - Wednesday, September 28, 2011 - link
yep and GDDR5 is a variant of DDR3 whereas GDDR3,4 were variants of DDR2, so essentially the same base specDanNeely - Tuesday, August 23, 2011 - link
GDDR has split from main stream DDR standards and undergoes more frequent, smaller updates. Among the advantages they have is that since the chips are soldered onto the GPUs and aren't user swappable they don't have to as extensive validation to make sure every part combination works. One major functional difference is that (in most cases) each GDDR chip is connected directly to the GPU by a dedicated instead of being glued together into dimms that share a connection to the CPU.