[SOLVED] That weird PCIE 4.0x2 M.2 slot... quick question

NWCherokee

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Would a PCIE 4.0 drive like the WD 750SE that has similar performance to PCIE 3.0x4 drives be a good choice for an M.2 slot on a X570 board with a 4.0x2 interface? If I use loose math, a 3.0x4 and a 4.0x2 offer the same relative bandwidth, but would the WD750SE be further knee-capped? Just curious as I have an empty 4.0x2 m2 slot and looking for an inexpensive drive to fill it with and a 500GB SN750 SE is going for $49.99 at B&H right now. Not going to be an OS drive, just additional storage. Any drive will be fine for my usage, but might as well get something faster for similar cost. Is this the one actual use case that makes this drive stand-out?
 

NWCherokee

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Feb 12, 2021
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Real world experience aside, I know I wouldn't be able to notice much if any difference... but I am still curious just the same.

When installing a 3.0x4 drive in the 4.0x2 slot, sequential drive read/write is capped just below the 2k mark since it is still only using 2 lanes at 3.0 regardless of the greater bandwidth of the 4.0 m.2 slot.

Would the WD Black 750 SE suffer the same capping (being a Gen 4 drive with mid 3k read write speeds), or would it be able to still reach near its rated speeds since even in a 4.0x2 slot its maximum performance would still be under the theoretical limit of the 4.0x2 lanes?

What other hardware limitations may be in play?
 

NWCherokee

Prominent
Feb 12, 2021
11
3
515
0
Real world experience aside, I know I wouldn't be able to notice much if any difference... but I am still curious just the same.

When installing a 3.0x4 drive in the 4.0x2 slot, sequential drive read/write is capped just below the 2k mark since it is still only using 2 lanes at 3.0 regardless of the greater bandwidth of the 4.0 m.2 slot.

Would the WD Black 750 SE suffer the same capping (being a Gen 4 drive with mid 3k read write speeds), or would it be able to still reach near its rated speeds since even in a 4.0x2 slot its maximum performance would still be under the theoretical limit of the 4.0x2 lanes?

What other hardware limitations may be in play?
UPDATE:

I did purchase a $49 500GB SN750 SE and can confirm that it does pretty much reach its rated speeds in a PCIE 4 x2 M2 slot. On its own, the WD SN750 SE doesn't make much sense at first glance as a gen 4 drive with gen 3 speeds, but I think I found the one niche where it works.

If I was to put in a Gen 3x4 or Gen4x4 drive in my gen4x2 slot I only get half of the performance. Since the SN750 is already a gen 4 drive with half the performance I maximize the value for the gimped m2 slot. Essentially, if you have a motherboard with a gen4x2 slot, the SN750 SE is the best bang for your buck ATM and a backdoor way to get performance equal to a fast Gen3 drive without having to spend gen4 money to do it... You get a drive that will be faster than any gen3 drive in that slot and a drive that costs way less than a typical gen4 drive.

Not that you will be able to tell the difference, but I just wanted to post this from a straight numbers perspective if anyone was interested.
 

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