Hacker News Reader

Comment by ohgodplsno | Hacker News Reader

Don't get too excited: unless your usecase is about pulling out massive amounts of data organised in a linear fashion out of RAM in a single read, DDR5 is kind of crap for real world usage. Current DDR5-4800 kits (which are pretty much the only things that will work on non-enthusiast hardware) will perform usually worse than a regular DDR4-3200 at most tasks, for a single reason: latency. Most DDR5 these days have a latency of 20ns, compared to 10ns of DDR5. Any bandwidth gains will be destroyed by the fact that you're doing a thousand reads anyways.

However, if your usecase is sequentially reading massive chunks of memory, this will be useful for you. But dear god am I afraid of seeing the latencies on these beasts.

View on HN

I am not sure that is accurate. I just looked at the inventory of my local computer parts store. They are selling Crucial DDR4-3200 DIMMS with CL22, and Crucial DDR5-4800 with CL40. DRAM latency is measured in clock cycles, so this difference is only +21%, not +100% as you suggested. Same for DDR5-5600 with CL46. The CAS latency is higher in clock terms but not in wall-clock terms.

(latency = CL * 2000 / hz)

CL22 is also pretty damn bad, most DDR4-3200 kits now have CL16, which makes them 10ns. But even then, your DDR4-3200CL22 has 13.75ns, your DDR5-5600CL46 has 16.5ns. and that is assuming your PC will handle a 5600, which isn't the JEDEC standard, so most OEMs can say goodbye to it.

Oh really? It is the supported memory type written on the box of my Intel processor.

Once again, the subject is not you buying your processor individually (enthusiast hardware), but your run of the mill, 80% of people have it OEM stuff. Your tower PC bought at the local supermarket, your laptop, all of these will have a combination of:

* CPU not supporting such a high rate

* Motherboard not supporting it

* CPU lost the silicon lottery and has a bad memory controller that struggles above basic rates

* vendor put in DDR5-4800 in anyways to save up on costs

* BIOS not up to date on your motherboard

But what you said is, it’s not a standard. And I’m looking at a press release from 2021 that says it is.

> JESD79-5A expands the timing definition and transfer speed of DDR5 up to 6400 MT/s for DRAM core timings and 5600 MT/s for IO AC timings to enable the industry to build an ecosystem up to 5600 MT/s.

Jesus fuck, thanks for reminding me that HN is full of needlessly pedantic assholes.

JEDEC _default_, not standard. Satisfied ? As in, the default value is 4800, and now, with JESD79-5A, JEDEC also recognizes that DDR5-6400 can exist. Not "is the standard".

Hey if you don’t want to have this conversation, stop repeating stuff you read on Reddit but don’t understand.

How do you define "non-enthusiast hardware"? All consumer AMD CPUs should be able to clock up to 6000 MT/s and Raptor Lake should do 6600 MT/s stable at the very least with Hynix M-dies. 5600 MT/s is not even an overclock on Intel CPUs.

>How do you define "non-enthusiast hardware"?

That OEM motherboard in your big box tower.

>All consumer AMD CPUs should be able to clock up to 6000 MT/s and Raptor Lake should do 6600 MT/s stable at the very least with Hynix M-dies. 5600 MT/s is not even an overclock on Intel CPUs.

DDR5 speeds currently crash like a rock if there's more than one DIMM per channel, even moreso if those DIMMs have two ranks rather than one.

I've got four sticks of 16GB DDR5 5600MHz in my Intel i7 12700K, Z690 system. The best I can get the RAM going is 4800MHz, which is still an overclock because Intel's memory controller goes down to 4000MHz rated clock speed with this setup (two DIMMs per channel, 1 rank per DIMM).

Yes, that currently doesn't work well, but most people are using 1DPC, not 2DPC. You can't really even find a kit with 4 DDR5 sticks.

>You can't really even find a kit with 4 DDR5 sticks.

You can: https://www.newegg.com/corsair-64gb/p/N82E16820236933

Maybe once prices come down more I'll consider going to two sticks of 32GB instead of four sticks of 16GB, who knows.

At least in my country (New Zealand) only Newegg (which ships from US and has very expensive shipping) seems to have these 4 stick DDR5 kits and only from Crucial and they are all more expensive than a 2 stick kit with the same capacity, so I'm not sure why anyone would get them.

There weren't any 32GB sticks back when I put my system together, so it is what it is. :V

Populating all of your RAM slots with matched RAM improves your overall bandwidth. A 2x8GB set will run in dual-channel mode, the 4x4 set will run in quad-channel mode (if the CPU supports it, most times it's dual-channel.) The 4x4 set will allow for more bandwidth vs the 2x8. Not quite double, but it reaches at it. Every other metric doesn't really see much of an improvement, though, so this only helps out in bandwidth-intensive applications.

In my (and probably most peoples') case I'm running in dual channel, so that's two 16GB DIMMs per channel. This makes the memory controller clock down to 4000MHz rated.

>You can't really even find a kit with 4 DDR5 sticks.

https://www.corsair.com/ww/en/Categories/Products/Memory/VEN...

4 X 48GB DDR5 5200 40CL latency. G-Skill just came out with some new kits that are even faster.

> DDR5 speeds currently crash like a rock if there's more than one DIMM per channel, even moreso if those DIMMs have two ranks rather than one.

How would you determine that with dmidecode?

Overclocking _is_ enthusiast behavior, and you can pretty much only do it with enthusiast hardware. As another person told you, if you're buying your components yourself, congratulations, it's enthusiast hardware. Many will still get laptops (that do not allow overclocking), or crappy motherboards from OEMs (that do not allow overclockingà.. The current reality of things is that DDR5-4800 is the default JEDEC speed, and that's it's crap. The same way that DDR4-2133 used to be the default JEDEC speed, and now things got better and 3200 is the default without overclock.

Reply on news.ycombinator.com