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cynan
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The Skinny on Single Channel RAM in new laptops

Sun Nov 26, 2017 8:12 pm

What sort of performance hit can I expect from an identically specced laptop (with something like a core i5/5 15W chip or Ryzen Raven Ridge) with only one (vs two) memory channels?

I recently ordered a Lenovo Ideapad 720s and discovered that, to my horror and disbelief, there is only a single DIMM slot and no sign of soldered RAM. I noticed that a couple of Lenovo's newer laptops (and not just their low end stuff) seem to be designed with only single channel memory. The laptop is otherwise nicely specced for the price (around $770 with i7-8550, MX150, 8GB ram, 256GB NVMe SSD).

I noticed some snickering in the Rzyen 2500/700 Raven Ridge announcement thread that some of the launch laptops were only single channel... Elsewhere there seems to be opinion that due to better cache management in newer CPUs, single channel ram for a 15W CPU (level of performance) may not be that much of a detriment.

Is single channel ram for an "ultrabook" really that bad?
 
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Re: The Skinny on Single Channel RAM in new laptops

Sun Nov 26, 2017 8:35 pm

Something immediately obvious is probably a lack of iGPU performance, but assuming that the system either already has a dGPU with its own memory, or you're not intending to game on it, it probably wouldn't matter much in my experience. Though I've only seen single-channel DDR3-1600 IRL (by way of my current rig when it's sans my usual functional RAM and having to run a cheapo stick for a while)... in practice it didn't seem to affect performance much during normal use.
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Re: The Skinny on Single Channel RAM in new laptops

Sun Nov 26, 2017 8:36 pm

It is if you are using the iGPU.
 
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Re: The Skinny on Single Channel RAM in new laptops

Sun Nov 26, 2017 9:46 pm

cynan wrote:
I recently ordered a Lenovo Ideapad 720s and discovered that, to my horror and disbelief, there is only a single DIMM slot and no sign of soldered RAM. I noticed that a couple of Lenovo's newer laptops (and not just their low end stuff) seem to be designed with only single channel memory. The laptop is otherwise nicely specced for the price (around $770 with i7-8550, MX150, 8GB ram, 256GB NVMe SSD).

That's pretty cheap for an 8th gen i7 + MX150 + 256GB NVMe...that may have been a giveaway that there was SOMETHING amiss. The Acer Swift 3 that TR just reviewed with an i5 is going for 720 USD right now. Click me. The i7 version is going for a whopping 999. The Swift systems appear to all have dual channel RAM, too.

I'm not quite sure you'll see any issues with the MX150. It appears to have its own GDDR5. You'll probably be OK, but if it were me, I'd probably return it and look around for something with a dual channel RAM implementation.
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cynan
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Re: The Skinny on Single Channel RAM in new laptops

Sun Nov 26, 2017 10:10 pm

Yup. But the specs are pretty good for the price. It also has Thunderbolt 3 (I believe the Acer Swift 3 does not) and the IPS screen is apparently better (brighter, anyway) on the Lenovo vs the Acer. The Lenovo is also 3/4" narrower due to slim bezels, and overall, it looks a tad nicer than the Acer.
Last edited by cynan on Sun Nov 26, 2017 10:15 pm, edited 1 time in total.
 
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Re: The Skinny on Single Channel RAM in new laptops

Sun Nov 26, 2017 10:12 pm

If it was me I'd ask for a refund. This would be a case of form over function or Lenevo giving you a less than optimal product to cut costs. Problem is the iGPU craves bandwidth plus the CPU cores need their share of bandwidth no matter the prefetch logic plus the amount of L2, and L3 Cache have to prevent accessing DDR4 RAM.
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Re: The Skinny on Single Channel RAM in new laptops

Sun Nov 26, 2017 11:15 pm

cynan wrote:
Yup. But the specs are pretty good for the price. It also has Thunderbolt 3 (I believe the Acer Swift 3 does not) and the IPS screen is apparently better (brighter, anyway) on the Lenovo vs the Acer. The Lenovo is also 3/4" narrower due to slim bezels, and overall, it looks a tad nicer than the Acer.


I didn't and don't disagree that the specs are good for the price. The dual channel thing sucks, and I imagine there are a few more shortcuts they had to take to get it down to 770. If you're happy with it, then that's all that matters really, but I would be at least a little bit cautious.
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Re: The Skinny on Single Channel RAM in new laptops

Mon Nov 27, 2017 12:12 am

You said the RAM wasn't soldered and that it was single channel. Was there a second open SODIMM slot then? (you said there was only one slot, but I just want to make sure you meant what you said)
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Re: The Skinny on Single Channel RAM in new laptops

Mon Nov 27, 2017 1:30 am

I kinda subscribe to buy once cry once camp, the 920 is worth the extra dough if you want a really nice ultrabook. There were a couple good but not really advertised sales over the holiday week, gone now though ofc.
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Re: The Skinny on Single Channel RAM in new laptops

Mon Nov 27, 2017 5:40 am

DPete27 wrote:
You said the RAM wasn't soldered and that it was single channel. Was there a second open SODIMM slot then? (you said there was only one slot, but I just want to make sure you meant what you said)

It is surprising to me that the official specs and many online reviews don't mention how many RAM slots there are, or whether the RAM is user-upgradeable. I guess Apple has brainwashed the masses into thinking that laptops are a "no user serviceable parts inside" appliance.

What I've been able to find indicates that there is indeed a single, non-soldered SODIMM.
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Re: The Skinny on Single Channel RAM in new laptops

Mon Nov 27, 2017 6:45 am

Just buy the fastest RAM you can for that slot.

Given the TDP constraints of the form factor, and the fact that the laptop doesn't need the bandwidth for its IGP, I doubt that memory bandwidth is going to be the bottleneck in the majority of your use.
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cynan
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Re: The Skinny on Single Channel RAM in new laptops

Mon Nov 27, 2017 8:33 am

Bauxite wrote:
I kinda subscribe to buy once cry once camp, the 920 is worth the extra dough if you want a really nice ultrabook. There were a couple good but not really advertised sales over the holiday week, gone now though ofc.


The 920 is a nice premium design , with a definitively nicer, sleeker chassis. But is it worth the extra dough if your chief goal is not to own the sleekest, prettiest 2-in-1? It costs at least 50% more than the sale price for the 720s and if you want an i7 over an i5 and 16gb ram, you'll likely have to pay closer to 100% more.

With the 920, you also have to live with the igpu. And even though the 720s is single channel, I still have the option of swapping in a 16gb dimm down the line. The ram in the 920 is all soldered.

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