How can an M2 undetected by the BIOS be detected by Windows 10?

Hi
I bought an Acer Nitro 5 (label enclosed). It came with a factory installed M2 and two additional free slots. I added a second M2 (label enclosed), and also an SSD.
The SSD is detected by the BIOS but the M2 doesn't show in the BIOS (pic enclosed). Surprisingly, although it is undetected by the BIOS it still shows up in Win10 and works OK (screengrab enclosed).
Would someone be able to explain this to me? I would assume that something that is not detected by the BIOS would also not be detected by the operating system. Also, why is it not detected by the BIOS?
Thanks

Note: Win 10 Pro 22H2

Because the Bios only needs to know what your boot drive is at a bare minimum requirement.

There is several areas that can effect the outcome you are describing and i cannot recall exactly but windows will use pnp to map devices and it can be down to how your device bus on the motherboard are read etc.

There is lot of factors to it that can effect it just know that the bios only needs to know which drive to boot at minimum, if you have in the bottom right task bar the drive showing as ejectable then you know it got detected as a pnp device.

what is the make and model of the ssd ?

the AN515-57 seems a recent machine , but that bios sceen looks ancient.

It will be UEFI still but they never made a fancy GUI for it. This can be common on OEM machines as it will most likely be down to time saving or money saving or both. Cutting corners where they can because time is money.

[QUOTE=Bree;2524597]Welcome to Ten Forums.

I think it's the the other way round, it's SSD that's not showing. The model and serial number of the M2 in your photo is the same as the HDD2 in the bios screenshot.

You have a keen eye. Indeed it is the SSD, and not the M2 that is undetected by the BIOS. Why did I believe it to be the M2? Well, for reasons that make this story even weirder! When I first entered Windows after I installed the M2 and the SSD only one additional disk was showing. I tested it with Crystal Disk Mark in an effort to find out if it was the SSD or the M2 and I got a writing speed of around 500 MB/s. I tested the system disk and I got a speed of around 3000 MB/s, so I assumed the recognised disk was the SSD. After I had finished these test a third disk suddenly appeared, so I assumed it was the M2.
I have just tested the three disks and oddly both the M2 and the SSD have similar speeds, while the system disk that came with the Nitro is noticeably faster. This doesn't make much sense either, does it? The mystery thickens.
Enclose please find the speed tests.

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SIW2 said:

what is the make and model of the ssd ?

the AN515-57 seems a recent machine , but that bios sceen looks ancient.

The BIOS looks extremely primitive yes. According to CPU-Z the motherboard is a Scala TLS, manufactured by TGL, and the BIOS' brand is Insyde Corp.
This laptop was manufactured in 2022 though...