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Alder Lake Tested With DDR5-6400 Memory, Has Unexpectedly High Latency

Intel 12th Generation Alder Lake
(Image credit: Intel)

A new Alder Lake benchmark has been posted with a for sale listing, potentially showing Alder Lake running in its new Gear 4 mode. According to @harukaze5719, this latest leak comprised a Core i5-12600K 10-core CPU running the AIDA64 cache & memory test, with a kit of DDR5 memory operating at DDR5-6400. Memory bandwidth was impressive at around 88-90GBps. However, memory latency took a huge hit, running at a sluggish 92.5ns. 

According to the listing, the system ran with Gear 4 enabled. In the last decade, Intel hasn't released a single architecture that approached 92.5ns of memory latency. Only AMD's original Zen architecture was capable of such laggy behavior, and it was known for its memory bottlenecks in that first-generation iteration.

Alder Lake i5-12600K AIDA64 benchmark

(Image credit: Twitter)

Intel first introduced gear modes with its current Rocket Lake architecture as a way to improve memory support, but at the cost of latency. Rocket Lake offers up two modes:  Gear 1 and Gear 2. Gear 1 is the default mode that will run the memory controller and RAM at the same frequency, resulting in very low system latency. Gear 2 on the other hand reduces the memory clock to run at half the speed of the memory controller clock, or a 2:1 ratio. You sacrifice some memory latency, but you reach higher frequencies, and thus higher bandwidth, as a result. 

When we tested both gears in our Rocket Lake review, we noticed Gear 2 took a noticeable toll on system latency, directly impacting gaming performance. We tested a Core i5-11600K with Gear 1 mode featuring DDR4-2933 RAM, and DDR4-3200 RAM for Gear 2. Despite the faster memory speeds on Gear 2, we found that Gear 1 was consistently faster, with 5% better gaming performance. The memory latency results showed a similar trend, with 59.3ns for Gear 2 mode and 52.3ns for Gear 1. The latency results would be even more pronounced if both configurations ran at the same RAM frequency.

With Gear 4 mode, Intel takes things to a whole new level by cutting the memory controller frequency to just a quarter of the memory frequency. While this does allow the chip to support incredibly fast memory, it should still result in large latency losses.

So if the leaked latency results are true, with Gear 4 nearly doubling the amount of memory latency of Gear 1, then that setting will probably be quite useless for PC gaming and for other consumer-based applications. Generally, system latency is far more important than memory bandwidth, with only a couple of memory-hungry apps actually breaking that rule. So we'll have to see how these changes materialize once Alder Lake launches later this year.

The biggest unknown to all this is DDR5 memory, and what the highest memory frequency will be for the most expensive DDR5 kits. We've already seen DDR5 kits that can hit 12600MT/s, so Gear 4 mode could be advantageous at these speeds and beyond. But for now, it's only a theory. We'll have to wait for reviews (or at least a few more leaks) to see how the new Alder Lake architecture handles DDR5, and if higher gear modes will actually be useful.

  • InvalidError
    In other words: business as usual.

    Historically, the fastest memory on a new standard comes at the expense of increased latency and you are better off using reasonably fast low-latency previous-gen stuff for most workloads. It has always been that way as far as I can remember so I would never buy first-gen memory or first-gen CPUs on new memory, too many things need to get tweaked on both sides before next-gen memory gets a mostly clean benchmark suite sweep for a palatable markup over premium but still cheaper previous-gen stuff.
    Reply
  • wifiburger
    horrible latency, not sure why we need 80Gb/s+ for bandwidth on consumer chips
    I would bet not even 16core will make use of it

    If that was the case, we would of got 3 or 4 channel DDR4 by now with Ryzen cpus

    If DDR5 needs Gear4 , no amount of speed will recover that crazy latency.

    Usually Intel is considered the best when it comes to memory controllers ... wonder what AMD latency will be lol
    Reply
  • mattkiss
    Gear 2 on the other hand reduces the memory clock to run at half the speed of the memory controller clock, or a 2:1 ratio.

    Don't you mean the other way around?
    Reply
  • derekullo
    More Tesla Semi than Model S.
    Reply
  • InvalidError
    wifiburger said:
    horrible latency, not sure why we need 80Gb/s+ for bandwidth on consumer chips
    I would bet not even 16core will make use of it
    16 cores is getting bottlenecked by dual-channel DDR4 in many workloads, so DDR5 will be very much necessary for consumer CPUs to scale beyond that. More system memory bandwidth will also be great for future IGPs and the latency of affordable DDR5 should be considerably better by then, along with the overall performance of 2nd/3rd-gen DDR5 controllers.
    Reply
  • JWNoctis
    I'd expect much larger L3 cache and/or some exotic kind of L4 cache going mainstream, while DDR5 lasts. What's the typical latency of an on-module HBM2 stack?

    Even then, there are still those workloads where no reasonable amount of cache is going to help. Not that there are many in client space, though.
    Reply
  • Phaaze88
    Simply put: exercise patience, don't early adopt, except if circumstances force you to do so - and even then, Ryzen is an alternative...
    Reply
  • InvalidError
    Phaaze88 said:
    Simply put: exercise patience, don't early adopt, except if circumstances force you to do so - and even then, Ryzen is an alternative...
    Zen 4 will be on DDR5 too and I'd expect it to have similar issues with DDR5 until lower latency DDR5 equivalent to today's 3200-16 bargain basement stuff becomes readily available.

    Keep in mind that 6400-40 is 25% worse CAS latency than today's relatively cheap and plentiful 3200-16.
    Reply
  • Phaaze88
    InvalidError said:
    Zen 4 will be on DDR5 too and I'd expect it to have similar issues with DDR5 until lower latency DDR5 equivalent to today's 3200-16 bargain basement stuff becomes readily available.

    Keep in mind that 6400-40 is 25% worse CAS latency than today's relatively cheap and plentiful 3200-16.
    Well... never mind.
    Just wait, except if forced to do so.
    Reply
  • R4DIO4CT1VE
    Yeah I'll let someone else pay for this before I adopt
    Reply