I have dell inspiron 7520 which its original configuration have only 1 hdd and 1 dvd bay and have no m2 ssd bay on the mother so I decided to switch from the 1 tb hdd to an 2.5 inch ssd to accelerate my os and programs but i can not afford an 1 tb ssd so i decided to go for 240 gb ssd and keep my 1 tb hdd and install it in 2nd hdd cuddy in replacement to the dvd bay so by exploring bios settings i found these 3 choices in serial communications tab and i can not decide what would give the best performance and still be compatible and does not affect my computer reliability as I heard that some of these choice would not fit my configuration and my motherboard
Intel Smart Response is only useful if you have an M.2 SSD installed AND you intend to use it as a caching module for a 2.5" spinning drive, but you would never use a caching module with a 2.5" SSD. ATA is a legacy option for very old OSes.
AHCI is the best choice for your configuration. That would be true even if you decided to add a regular M.2 SSD later.
I do not have an m2 ssd bay on my laptop it exists only on the special edition is ahci safe for my ssd in closing and opening as i heard some people face some unexpected power loss for ssd as result of choosing ahci is it compatible to my system or not
Yes, as I said originally, AHCI is the correct setting for a 2.5" SSD. It does not affect the safety of your data during a power loss. You are probably thinking of setting like "write cache buffer flushing" that are configured within Windows.