Why Has the Size of TObject Doubled In Delphi 2009?
Because it has a new feature.
Mason Wheeler noticed that TObject.InstanceSize returns 8 (bytes). It turns out that this is new in Delphi 2009; in previous releases, TObject.InstanceSize returned 4. But when you look at the definition of TObject in System.pas, you don’t see any fields declared at all.
Four out of the eight bytes are consumed [...]