The 36–Month Unlimited Plan 1-Server for Mac OS X from Apple is a 3 year agreement payable in advance. During this period you get all the major upgrades to the Mac OS X Server Software product.
To be eligible for the Server Maintenance program you must be licensed for the current version of Mac OS X Server.
Each maintenance license is limited to the corresponding license owned by you for the current version of Mac OS X Server. This will cover all update releases for 3 years.