Can someone point me to a short reference

[d***@gmail.com]

I have some code using EJB's. I want to know a couple of simple
answers.
How does one know if EJB v1.0, v2.0, or v3.0 are being used.
Are they backwards compatible?
I read an ariticle which discussed how certain things were made
simpler in v3, but my fundamental question is will old code still
work.
Are EJB's tied to a particular J2EE?
Somewhere I have read that one should use EJB with J2EE1.5.

[d***@gmail.com]

I heard that they are backwards compatible, e.g. EJB 3.0 supports EJB
1.0 targeted code.
I was told to look at the EJB descriptor field, which should specify
the version.