When remediating ESX hosts, Update Manager handles patches in different ways depending on the ESX host version.
In the ESX 4.x patch remediation process, Update Manager operates with VIBs (.vib files). A VIB is the smallest installable unit on an ESX 4.x host. A bulletin defines a specific fix for a host, a rollup that aggregates previous fixes, or an update release. When a host is compliant with all bundles in a bulletin, it is compliant with the vSphere bulletin that contains the bundles.
If a bundle depends on other bundles, Update Manager installs the necessary prerequisite bundles during the remediation process. As a result, the number of patches after staging and remediation might be greater than the number of patches that you selected for staging or remediation. For example, when you stage or remediate a host against a baseline consisting of a bulletin that contains bundle A, and bundle A requires bundle B (bundle B is not part of the bulletin), both bundles get staged or installed. In such a case, the patch count for staged or installed patches is two, not one.
Update Manager 5.5 supports upgrade from ESXi 4.x, ESXi 5.0 and ESXi 5.1 to ESXi 5.5 and migration from ESX 4.x to ESXi 5.5. You cannot use Update Manager to upgrade a host to ESXi 5.5 if the host was upgraded from ESX 3.x to ESX 4.x. Such hosts do not have sufficient free space in the /boot partition to support the Update Manager upgrade process. Use a scripted or interactive upgrade instead.