When installing RAM memory in QNAP TS-x73 we need to know what slots to use because there are 4 slots labelled A1, A2, B1, B2.
When looking at the NAS from the side, with the motherboard and RAM in front of you, the slots are labelled from left to right in this order : B2, B1, A2, A1.
The manual says that there are 4 slots, from 1 to 4. In my case the correspondence is:
slot 1 – B2
slot 2 – B1
slot 3 – A2
slot 4 – A1
So for 1 DIMM use slot 1 (B2)
For 2 DIMMs use slots 1 (B2) and 3 (A2)
Link for the manual is below or on the QNAP site: