For you that also have Motherboard with legacy BIOS, eventhough the mobo doesnt have nvme slot, by using NVME m.2 with PCIE adapter we can still use nvme m.2 drive.
If you guys think there wont be any speed improvement, by using NVME compared to SSD in old mobo, I think you are wrong, even in old mobo which still have PCIE 2.0, using NVME is still 400% faster than using fastest SSD.
Here is comparison I took by my self with my system comparing WD Black, Samsung 860 EVO and ADATA SX8200.
System used :
ASUS P6X56D Premium
Intel Xeon X5680 @4,4Ghz
4x8GB DDR3
@triple Channel
Marvel Controller SATA 3 --> 2 drive --> SAMSUNG 860 EVO 500GB (Boot Drive) & HD WD Black 1TB
ADATA SX8200 PRO 512GB connected in 2n PCIE slot with PCIE adapter
NVME definitely faster in X58 compared to SSD, NVME is faster 400% from SSD, and 1600% faster from HD, that is why it should worth to try to use NVME even on old mobo
However, booting from NVME drive in old mobo is another issue

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