Difference between AX-2009 to Ax-2012

There are many difference. Below are few points:

Models and the Model Store

Object IDs

The AxUtil Command Line Utility and PowerShell Cmdlets

Development Workspace

Some Layers Have Been Renamed

S.No	Microsoft Dynamics AX 2009	Microsoft Dynamics AX 2012	Why is this important?
1.Models and the Model Store	The model store did not exist in Microsoft Dynamics AX 2009. Application model data was stored in .aod files. You can load .aod files during version upgrade. You can also load .aod files by using the Tools menu.	The following model features are new: 1. A model is a set of model elements in a specific layer. 2. Each layer consists of one or more models. One of the models is generated by the system. For example, VAR Model is the model that is generated for the VAR layer. 3. Each element in a layer must belong to only one model. 4. Models can be exported to a file artifact that is called a model file. Model files have an .axmodel extension. A model file is like an .aod file from earlier versions, but the names and numbers are not limited. Models in the model store can be exported to model files and imported from model files. Model files can be signed, and the signature is verified when the model files are installed. 5. Model files replace .aod files as installation artifacts. 6. Models in the SQL Server–based model store replace .aod files that were used at run time. 7. The Application Object Tree (AOT) shows you which model a particular element belongs to, in addition to the layer tags.	Storing models in SQL Server increases quality, reliability, and performance. In addition, you can use the tools that are available in SQL Server for backup and administration

2.Object IDs	Object IDs were 16 bits long	Object IDs were 32 bits long	Changing the length of object IDs from 16 bits to 32 bits exponentially increases the number of object IDs that are available
3. The AxUtil Command-Line Utility and PowerShell Cmdlets	The feature was not available	AxUtil is a command-line utility that you can use to import and export .axmodel files into the SQL Server model store. You can also use AxUtil to delete one or more models, create new empty models, and list all of the models in a layer. All of the capabilities of AxUtil are also exposed as PowerShell CmdLets.	Users can use these tools to work with models from outside the development environment. Therefore, there are more options for scripting deployment processes
4.Development Workspace	Development occurred directly in the Application Workspace	The Developer Workspace contains all of the tools and features that a developer must have to create and customize a Microsoft Dynamics AX application. Changes that you save in the Development Workspace are always synchronized with the Application Workspace. You can still open application elements in the AOT. You can also open an Application Workspace from the Development Workspace to view your customizations. You can open Microsoft Dynamics AX directly from a Development Workspace by using the Ax32.exe command-line flag	The new Development Workspace provides a more streamlined environment for writing code. The menus have also been customized to make it easier to find the tools and commands that you use when you write code