Parent document is top of "Atari 8-Bit Computers: Frequently Asked Questions"
Previous document is "13.5) What BBS software can be used on the Atari?"
Next document is "13.7) Which versions of the Operating System (OS) are there?"

13.6) What versions of Atari BASIC or the CTIA/GTIA chip do I have?

Atari BASIC:

At the READY prompt, enter "? PEEK(43234)"

If the result is:  You have Revision:
     162                  A
     96                   B
     234                  C

Freddy Offenga, mailto:offen300@hio.tem.nhl.nl adds:

there's another good answer (IMO):

You can also take a look at the part numbers on the IC's
inside your Atari and compare them with the numbers from
the following table:

Part#                  Version
~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~
CO12402 + CO14502         A
CO60302A                  B
CO24947A                  C


CTIA or GTIA installed?

In BASIC, type POKE 623,64 [RETURN] and if the screen blackens, you have the
GTIA chip.  If it stays blue, you have the old CTIA chip.

By the way, apparently no CTIA-equipped Ataris were shipped to Europe.