A:Answer In fact, M.2 SSD are classified into PCI-Express-based and SATA-based SSDs.
And i just got the review on G501VW from gaminglaptopsjunky.com, which seems to be reliable.
Storage HDD : HGST 1TB HGST HGST HTS541010A7E630
SSD: None
M.2 slots: M.2 SATA or PCIe/NVMe 2280 (one)
According to the provied storage information, it explicitly indicated that G501VW is compatible with both SATA-type M.2 and PCIE-type M.2 SSD(BTW the latter is more powerful and expensive).
Just remember you should pick the 2280 size. (M.2 SSD are classified as 2242, 2260, 2280 in size )