This article is from the The Terminator FAQ, by Karsten A. Loepelmann firstname.lastname@example.org with numerous contributions by others.
Reese (in T1) and Arnold (in T2) both refer to the Terminator as a "Cyberdyne
Systems Model 101". Reese adds "the 600 series had rubber skin. We spotted
them easy. But these are new." Obviously there is more than one variation on
the Model 101. In T2SE, after the chip-toggle scene, the Terminator reboots
and the startup data is shown from his point of view. In the top left corner
of the screen it says "Cyberdyne Systems Series 800 Model 101 Version 2.4".
Presumably, the metal endoskeleton is Model 101; the flesh-covered units are
I leave it to Van Ling, former Creative Technical Supervisor of Lightstorm
Entertainment, and annotator of the T2 illustrated screenplay (see section
7.1 for more details), to provide the definitive answer.
From: <email@example.com> (KiraProd):
Arnold is an 800-series terminator, Model 101.
This means that the infamous endoskeleton covered in living tissue is a
T-800. The fact that the aforementioned living tissue looks like Arnold
makes it Model 101. Therefore, all 800-series Model 101s look like
Arnold. An 800-series Model 102 would look like somebody else, but would
be essentially the same underneath, since it's a T-800.
Just thought I'd clear that up.