The ModuleList
In the System16 Info Block, there is the entry 'ModList Address' at offset 116, that points to this block. It's a chained structure with information on all modules that are currently loaded into memory and have been successfully initialized. Each entry is 128bytes long.

Ofs Size Description
0 8 ModID
8 2 Primary CodeDescriptor
10 2 Primary DataDescriptor
12 4 Absolute address in memory
16 4 Size of this module in bytes
20 4 Offset to the 'Mod_Load' Code
24 4 Offset to the 'Mod_UNLoad' Code
28 4 Offset to the 'Service Table'
32 32 ModuleName
64 ... Reserved

This table can be displayed by using the 'modlist' command from the command-prompt.