• Guest, The rules for the P & N subforum have been updated to prohibit "ad hominem" or personal attacks against other posters. See the full details in the post "Politics and News Rules & Guidelines."

Question SATA vs PCI 2.0 x16 PCI 3.0 x4 bandwidth confusion

maddogmcgee

Senior member
Apr 20, 2015
317
183
116
Hi

I need to buy a new hard drive. I would prefer a m.2 NVME drive but only have one slot in my b450 tomahawk. Should have gone the x570. RIP.

The drive will roughly be mid tier in performance.

Currently thinking of getting an expansion card and maybe stealing my wife's motherboard next upgrade (it has an extra nvme slot). I will use the 1, 4 and 5 slots.

The slot it is going in is a PCIe express 2.0 x16 slot so I should get 8 Gb/s vs the 6Gb/s of a SATA drive?

My second question is, my board supports m.2 PCIe 3.0 x4.... so a maximum link speed of 4Gb/s. Being slower than the SATA connection does not seem right to me? What am I missing? Is this an issue of looking at link speed when I should be looking an bandwidth throughput?

Thanks in advance
 

Attachments

Insert_Nickname

Diamond Member
May 6, 2012
4,411
950
136
The slot it is going in is a PCIe express 2.0 x16 slot so I should get 8 Gb/s vs the 6Gb/s of a SATA drive?
Actually, you'll get 1000MB/s from the slot. Bandwidth for a single PCIe 2.0 lane is 500MB/s compared to a SATA3's 6Gbit (750MB/s). So a x2 connection yields 1000MB/s.

Somewhat illogically, when moving to PCIe 3.0 a lane does not "double up" as PCIe 1.0 vs 2.0 but "only" jumps to 985MB/s. You still get almost double the bandwidth, but the speed is a bit lower due to using a different encoding scheme.

My second question is, my board supports m.2 PCIe 3.0 x4.... so a maximum link speed of 4Gb/s. Being slower than the SATA connection does not seem right to me? What am I missing? Is this an issue of looking at link speed when I should be looking an bandwidth throughput?
A PCIe 3.0 x4 connection is 32Gbit. Which works out at 4000MB/s. So there is plenty of bandwidth compared to SATA there.
 

maddogmcgee

Senior member
Apr 20, 2015
317
183
116
Thanks for the explanations. I knew I was going wrong. Seems like even the PCIe 2.0 will be fine for my needs, at least in the interim.
 

Insert_Nickname

Diamond Member
May 6, 2012
4,411
950
136
NO, there are several Asrock boards that I have seen in the Asrock forums that Will NOT "see" an M.2 on a PCIe add on card.
This goes for pretty much all boards. But just because you can't see the drive in the BIOS/UEFI doesn't mean it won't work. The OS (installer) will still see it just fine, and will boot from it no problem.
 

ASK THE COMMUNITY