Flash storage to ssd

It can be a bit confusing! What is a SSD? and what are Flash chips?

• A SSD is a discreet assembly which emulates a HDD. Just like a HDD is made up of parts: a controller and in the case of a HDD a platter(s) which hold the data. With SSD’s we have a controller and one or more Flash chips!
• Newer systems have removed the discreet assembly of the drive and intergraded it directly on the logic board in the same fashion RAM is not soldered to the logic board. We often call this solution as direct Flash chips as there is nothing removable.

So here you’re just replacing the SSD assembly following this guide MacBook Air 11" Early 2014 SSD Replacement and for the drive you have either the custom Apple drive or one of the custom 3rd party drives from OWC or Transcend. These are the better solutions, the last option is using a M.2 SSD via an adapter. While cheaper there is issues with the suability and durability of this solution!