pali, pali and pali

Dear Jim and other Pali scholars,

I have a simple question which will show up my complete
ignorance in this area.

Would you kindly explain to me, in brief, what are the differences
between different pali systems and which is considered to be
the most authentic?

I understand that  the Singhalese pali canon, for example,
maybe different from the Burmese or Thai pali canon, not just in
script (of course!) but in some of the words used. Is this right?
How many different pali canons are there and which ones are
mostly used by translators? How significant are these
differences? Perhaps there is just an article you can refer me to -
(I vaguely remember B.Bodhi discussing it in an intro.
somewhere)

Thanks in advance (as we say here in Chinese)!

Sarah