Does running RAM below spec reduce timing?

[YubiHunter]

Hey guys, I was looking to upgrade my laptop, and I found a nice bundle deal for an SSD and RAM kit that I want, which is $30 cheaper than buying those components individually. However, the problem is that my laptop chipset only supports DDR4 2666, and the RAM that is included in the bundle is a DDR4 3200 CL 22-22-22-52 kit. Now, I know that if I put those RAMs in, the speed will get capped at 2666, but will the CAS latency also decrease? Because if not, I am able to buy the same SSD and a DDR4 2666 CL 19-19-19-43 kit for $5 more than the bundle deal, which could be worth it if the 3200 kit gets a capped frequency and remained at the same timing. Given that my laptop BIOS is pretty locked down and gives me no options to adjust RAM settings, will the 3200 kit automatically run at a lower timing like how its speed is automatically capped? And if not, should I spend the extra $5 to get the 2666 kit, or does the difference in timing won't result in real world difference? 

 

[191x7]

Usually the timings would decrease. 

Even if they wouldn't, the difference is not something you'd really notice.

[porina]

Can't say with 100% certainty without checking the actual modules. Most laptop ram runs at industry standard JEDEC speeds/timings. If it includes a profile for lower speeds, it'll be fine. For example, below is what my laptop 3200 ram supports. Basically all the standard speeds/timings, and timings do tighten with reducing speed. What I don't know is if all modules will have all these profiles programmed as standard.

 

JEDEC timings table        CL-tRCD-tRP-tRAS-tRC @ frequency
    JEDEC #1        10.0-11-11-24-34 @ 733 MHz
    JEDEC #2        11.0-11-11-26-37 @ 800 MHz
    JEDEC #3        12.0-12-12-28-40 @ 866 MHz
    JEDEC #4        13.0-13-13-30-43 @ 933 MHz
    JEDEC #5        14.0-15-15-34-48 @ 1033 MHz
    JEDEC #6        15.0-16-16-36-51 @ 1100 MHz
    JEDEC #7        16.0-17-17-38-54 @ 1166 MHz
    JEDEC #8        17.0-17-17-40-57 @ 1233 MHz
    JEDEC #9        18.0-18-18-42-60 @ 1300 MHz
    JEDEC #10        19.0-19-19-44-63 @ 1366 MHz
    JEDEC #11        20.0-21-21-47-68 @ 1466 MHz
    JEDEC #12        21.0-22-22-50-71 @ 1533 MHz
    JEDEC #13        22.0-22-22-52-74 @ 1600 MHz
    JEDEC #14        24.0-22-22-52-74 @ 1600 MHz
 

My laptop does support 3200, so runs profile #13. I'd guess a system supporting 2666 might run either profile #9 or #10 depending on how it selects what it thinks is best. Perf difference isn't likely to be major. There is a small risk if the intermediate profiles aren't present, it might select a much lower one that is.

[An0maly_76]

This is an interesting question. Following.

 

Those familiar with my 5900X build no doubt remember my woes of crazy RAM-related issues.

 

This system HATED the original Ballistix I used

These were advertised as DDR4-3200, 16-18-18-36 timings @ 1.35V. DOCP detected as such.

 

My Asus Tuf B550-PLUS' QVL recommended Patriot PV432G320C6K, 16-18-18-36 timings @ 1.35V.

These were also advertised as DDR4-3200

 

The board's DOCP detected the Patriot DIMMs at some wonky 16-20-20-40. I had to manually set the timings to 16-18-18-36. No big deal, right?

 

Here's where it gets weird.

 

This system flat refuses to POST with the DRAM clock at 3200 with these DIMMs. Runs perfectly set to 2400, anything more gets a blank screen startup until it figures out it's not happy and jumps into BIOS. I've noticed no real performance issues with the RAM at 2400, I just can't for the life of me figure out why this is.

 

So, if timings can change based on memory clock speed, maybe the 16-20-20-40 DOCP auto-detect is accounting for this?

Edited January 15, 2023 by An0maly_76
Revised, more info

[aDoomGuy]

Well, when you set RAM to run at XMP the timings will generally loosen to keep the memory stable or in some cases to be on the safe side. So yes timings can be tighter (decrease) if you don't set XMP. Now, as a general rule higher frequency gives more gain than tighter timings. If I was you OP I would just get the cheapest RAM you can get because the difference is pretty negigible unless your laptop lets you overclock memory.

 

1 hour ago, An0maly_76 said:

The board's DOCP detected the Patriot DIMMs at some wonky 16-20-20-40. I had to manually set the timings to 16-18-18-36. No big deal, right?

Sure, if it's stable. No biggie.

1 hour ago, An0maly_76 said:

This system flat refuses to POST with the DRAM clock at 3200 with these DIMMs. Runs perfectly set to 2400, anything more gets a blank screen startup until it figures out it's not happy and jumps into BIOS. I've noticed no real performance issues with the RAM at 2400, I just can't for the life of me figure out why this is.

This is the Patriot memory, right? Have you tried setting XMP/DOCP and dialling in sub timings manually? My Patriot needs like crazy loose 800 set for TRFC

1 hour ago, An0maly_76 said:

So, if timings can change based on memory clock speed, maybe the 16-20-20-40 DOCP auto-detect is accounting for this?

Yeah, generally you have two DOCP/XMP profiles right? You for example got your 3200 CL16 and your 3000 CL15. So as frequency goes higher timings generally needs to become looser and since higher bandwith is your highest gain it's a worthwhile tradeoff.

[An0maly_76]

34 minutes ago, aDoomGuy said:

Yeah, generally you have two DOCP/XMP profiles right? You for example got your 3200 CL16 and your 3000 CL15. So as frequency goes higher timings generally needs to become looser and since higher bandwith is your highest gain it's a worthwhile tradeoff.

Yes, it is the Patriot memory freezing at 3200.

 

What I mean is, since the board DOCP does not agree with what the QVL says, were I to use DOCP's auto-detect of 16-20-20-40 at 3200, would this latency slide or whatever, loosen the timings to 16-18-18-36 as shown in the QVL, but let it run at 3200 still?

Edited January 15, 2023 by An0maly_76
Revised, more info

[aDoomGuy]

2 hours ago, An0maly_76 said:

Yes, it is the Patriot memory freezing at 3200.

 

What I mean is, since the board DOCP does not agree with what the QVL says, were I to use DOCP's auto-detect of 16-20-20-40 at 3200, would this latency slide or whatever, loosen the timings to 16-18-18-36 as shown in the QVL, but let it run at 3200 still?

That sounds weird, are you absolutely sure it's the exact same mem that's on your QVL?

 

16-18-18-36 is tighter than 16-20-20-40 so I doubt that would be more stable. If it crashes at the latter I doubt it would run at 16-18 etc. Try set 3200@16-20-20-40 and find your tRFC and set it crazy high and see if it's stable then bring it down as much as you can. You may also need to loosen your tFAW and tRC. If it is Asus board you should find a SPD page somewhere that will list the timings recommended for tFaw, tRC and the different tRFC.

[An0maly_76]

1 hour ago, aDoomGuy said:

That sounds weird, are you absolutely sure it's the exact same mem that's on your QVL?

 

16-18-18-36 is tighter than 16-20-20-40 so I doubt that would be more stable. If it crashes at the latter I doubt it would run at 16-18 etc. Try set 3200@16-20-20-40 and find your tRFC and set it crazy high and see if it's stable then bring it down as much as you can. You may also need to loosen your tFAW and tRC. If it is Asus board you should find a SPD page somewhere that will list the timings recommended for tFaw, tRC and the different tRFC.

Yeah, that's kind of the problem... Asus's QVL recommends 16-18-18-36 for this kit...

*see below*

But the damned board detects it at 16-20-20-40. What in the entire ----?

 

Though I'm wondering... It's been said that Ryzen prefer dual-rank DIMMs. I'm pretty sure mine are dual, but could this be a factor here, one way or the other? It runs fine at the 2400, I'm just wondering why it won't POST with the memory settings at 3200 with the 'recommended' timings.

 

Either way, it sounds like you're thinking the DOCP auto-detect timings of 16-20-20-40 might let it run at 3200?

 

Sorry if I'm derailing your thread, OP.

Edited January 15, 2023 by An0maly_76
Revised, more info

[YubiHunter]

10 hours ago, An0maly_76 said:

Sorry if I'm derailing your thread, OP.

No, problem man. I am learning new stuff from your discussion too

[An0maly_76]

@aDoomGuy@YubiHunter

 

And for anyone else interested, I enabled DOCP at those funky 16-20-20-40 timings and what do you know? Machine runs fine.