What's the locked file flag?

The Disk Utility Repair Permissions feature repairs only the ownership and permissions for items installed by Apple. However, this may resolve issues with third-party products.

The OS X built-in firewall inspects each incoming network connection to determine if it's allowed. Connections are allowed or denied on a per-application basis.

The locked file flag prevents anyone, including the item's owner, from editing an item. Only the item's owner can unlock the item to then allow modification.

The system keeps applications from interfering with one another by segregating their memory usage using protected memory. Mac computers with 64-bit-capable processors allow processes to run in 64-bit mode, which allows them to individually access more than 4 GB of memory.