All large objects are placed in a single system table called
pg_largeobject.
PostgreSQL also supports a storage system called
"TOAST" that automatically stores values
larger than a single database page into a secondary storage area per table.
This makes the large object facility partially obsolete. One
remaining advantage of the large object facility is that it allows values
up to 2 GB in size, whereas TOASTed fields can be at
most 1 GB. Also, large objects can be randomly modified using a read/write
API that is more efficient than performing such operations using
TOAST.