DDR5 memory is on its way, twice as fast as DDR4
pcworld.com
pcworld.com
Of course we expect every generation of Double Data Rate memory to double the data rate. But it's always been a bit misleading to say "twice as fast".
If you look at CAS latencies [1] then it's clear that memory speeds stagnated a long time ago:
This is a central reason why the cache size per thread has not changed much in the last 20 years (beside of course fabbing/yield limits). (And because caches are subject to a similar effect as Dennard scaling)
(btw. I wonder if it'd have been smarter by the memory industry if they specified latencies in absolute numbers (or relative to the memory array clock, not the bus clock), not bus cycles, since the rising latency numbers have been a marketing issue in every generation.)
Also, AMD for example uses stacked ram (HBM), but that needs very special packaging and active cooling. http://www.amd.com/en-us/innovations/software-technologies/h... https://en.wikipedia.org/wiki/High_Bandwidth_Memory
I doubt we will see a drastic improvement in DRAM latency unless the underlying process changes a lot (i.e. different physical storage mechanism or very different manufacturing).
However, cache is now huge. So, it's latency is usually less of an issue than sequential reads/writes and total size.
My suspicion is that amplifying the differential voltages produced by femtocoulombs of charge at 100% reliability is a harder problem than moving the DRAM chips closer to the CPU, and that speed-of-light has gotten the blame in "pop architecture" due to sloppy overgeneralization.
2*2 feet is long for a memory bus, but it's partially cancelled
out by the high velocity factor (sorry, "speed of electricity")
of 0.951 in parent's calculations. Instead, I'm going with 0.5*2
feet at a velocity factor of 0.5 for a 2ns roundtrip propagation delay.First word latency: DDR3 SDRAM 6.37ns = 1/156,985,871 of a second.
DDR is not really setup for random access, because it's setup for talking to L2/L3 cache not registers. tRAS ~= tCL + tRCD + tRP which kind of but not exactly exactly what you want for random access.
I don't understand your argument that the L2 and L3 caches tip the balance in favor of <#CAS>. If anything, I'd expect them to do the opposite, because the SRAM and DRAM both aim to exploit locality, meaning that better L2 and L3 caches would reduce #CAS faster than #RAS. Of course, armchair reasoning about such complex systems as memory controllers and caches can only go so far, so I wouldn't be shocked to be wrong, but I would certainly demand actual statistics before changing my view.
On the other hand sequential access bandwith is limited almost entirely by the external interface and has more to with economical factors (pin count is major part of IC price) than any physical limitations.
You're point isn't invalid but it's sort of misapplied. In fact the latency of DRAM on modern systems is dominated almost entirely by precharge time within the memory IC, which is about an order of magnitude slower than signal propagation. And it's not changing, either. DRAM cycles have been sitting at around 60 MHz for a decade and a half. We're dropping voltage as we shrink the cells, and so there's no net increase. Realistically signal propagation will never be the limit.
Anyway, if you actually trace the furthest bit of a ram chip to the CPU it's a longer path than you might think > 1 foot but < 3 feet.
As to my point tCL is a round trip latency and actually not that far from optimal. DDR is not designed for pure random access so much as cheap access to lot's of ram so yes there are many trade offs, but they are more reasonable when your close to hard limits.
Here is a picture, from the center of the CPU, to the bottom edge of the furthest part of the DIM then up. http://harddiskdirect.com/media/catalog/product/cache/1/imag...
PS: A DIMM is just over 5 inches wide and 0.7 inches tall so if was centered physically on top of a CPU that's 3 inches right there.
But, that's part of the CPU packaging, a signal needs to get to these pins on the bottom of the CPU and that takes time.
If an improvement can be done cheap and easy it will be done. Implementing a memory controller for DDR5 is probably a trivial job very similar to current DDR4.
Integrated GPUs has been on the rise for a long time. This is good news for reusing current memory controller designs while providing higher bandwidth.
And DDR4 can apparently support 128GB per module. Those apparently exist, but you can't find even a 32GB at Newegg.
http://thememoryguy.com/samsungs-colossal-128gb-dimm/
But that was the end of 2015, we are into 2017 and i have yet to see this again on the market. And they are likely very expensive.
I really hope DDR5 bumps the spec to 512GB rather then 256GB. Unfortunately the DDR memory / GB prices is actually on the rise. The only thing i could see changes in the market is when all the Fabs from China goes online in 2018, and China continue to pour in tens of billions of money in it.
And they better have, because Intel already standardized 2400 as the recommended speed for Skylake.
I bought last year DDR3 RAM, 2400mhz.
So, when DDR4 started to be sold, capped at 2133, DD3 2400 was already sort of easy to find (and it is faster than the DDR4 too, due to smaller latency, the few times I decided to run my computer in some OC competition that relied on RAM it ended on the top 1% of the air cooled machines despite not being an exceptional machine neither prepared to OC, Intel XMP runs crazy fast on my machine, the OC people I talked all said it was because of my fast DDR3 RAM).
I think our expectations are just getting higher.
Wirth's law is a computing adage which states that software is getting slower more rapidly than hardware becomes faster.
Computers with good SSDs and not too much bloatware (relevant on Windows) do feel faster to me than computers used to be.
I think people can get nostalgic accidentally and overestimate how fast things were in the past. I remember multi-minute loads for games on my Commodore 64. I remember multi-minute Windows 3.1 bootups. I remember watching a JPEG progressively creep in on the early web. I remember watching my school projects in C++ take noticeable time to compile despite what we would now consider their absurdly simple nature. I remember when I was reluctant to click on a 1MB download.
But you do want to avoid having a modern Windows machine on a slow spinning-rust hard drive. Yeow.
I've recently switched from 8GB MBA to 16GB MBP and to be honest, I'm not sure I've noticed any more speed above what's to be expected from any brand new machine before it gets bogged down with shit. My MBA used to be able to handle multiple big programs running in the background - 2 of the Adobe suite + Chrome + small stuff, so I haven't felt much use for the extra juice day-to-day, though I imagine the RAM is useful for video editing etc.
No one's asked me yet why these smaller SSD thingys are so much more expensive than larger hard drives, but I prepared the answer a long time ago:
They make your computer feel 10x faster.
Only cheapskates and the stubborn would pass on an SSD.
Even a year ago I was still going "eeehhhhhh, weeelllll, maaayybee..." but sometime in the last year I'd say we crossed over for any professional. It's no longer a matter of paying $100 for a big-enough spinning rust or $600 for a too-small SSD, now it's more like "Do I want a really fast 512GB or a slow 4TB for the same price?", which are both as of right now ~$150 give or take $30 depending on your quality needs. (I just checked.) That's still quite the spread on size, but you can fit a lot in 512GB.
Most likely not at all. Browser speed has more to do with network speed and browser/website design than your hardware. Browsers and websites still make poor use of multiple cores, and making sites performing well is a never ending chase between designers adding more ads, images and visual effects, browsers trying to figure out tricks to make coping with that possible and developers implementing those tricks.
Edit: the image name has 8GB NVDIMM in it, so yeah this isn't DDR5.
But for price/power-budget reasons, they ship with the DDR-3L option.
Games, for instance, seem to see only very small performance differences from changing RAM speeds.
Even if speeds don't improve perceptibly because the CPU is simply waiting for the human 99% of the time it still may benefit laptop battery time due to increased power efficiency and the CPU completing that 1% sooner and returning to low power states.
Yeah, and the GPU (at least a dedicated one) has its own VRAM, so accesses for which RAM speed would otherwise be important end up relying on VRAM speed, I assume.