This update improves overall stability and addresses a number of minor issues, including the following:

• Support for opening projects imported from GarageBand for iPad.  

The update is recommended for all users of Logic Pro 9.

Issues addressed with 9.1.3 include:

•  Resolves problems related to the support of Hyper-Threading

Issues addressed with 9.1.2 include:

• Improved compatibility with 6 and 12-core Mac Pro systems
• Support for iOS control surface apps that utilize the OSC protocol
• REX files now supported in 64-bit mode
• Improved compatibility with select Audio Unit plug-ins

The update is recommended for all users of Logic Pro 9.
For detailed information on this update, please visit this website: Logic Pro Release Notes