1.Layers [AX 2012]

From left to right, these are the most common layers available in a standard Dynamics AX system:

SYS > GLS > FPK > SLN > ISV > VAR > CUS > USR

Each layer is completely independent of the other layers.  You specify which layer to connect to when setting up the AX client profile.

The bottom layer will be the SYS layer and this is where the standard application code is located, and is only accessible by Microsoft.  Other layers like ISV (Independent Software Vendor), VAR (Value Added Reseller) can be accessed by entering keys that Microsoft provides for each layer except USR (User) which does not require a key.

Each layer has a corresponding patch layer above it.
The patch layers are designed to make it easy to incorporate updates in your application. The basic idea is that when a minor update or correction is made, it is distributed in a patch file.

Layer	Patch Layer
USR	USP
CUS	CUP
VAR	VAP
ISV	ISP
SLN	SLP
FPK	FPP
GLS	GLP
SYS	SYP

[Important]

The top layer will always be used

For Example:

If you are modifying any table in VAR and USR Layer,
It will not matter if you keep adding columns to the table definition in the VAR layer as those new columns won’t be available to the end user, as the USR layer takes precedence.

Interview Question:
1. Different types of layers (Ans above)
2.If you manipulate anything which layer would it affect?
Ans: The present layer where you are working and below of that layer.