Hello,
Diploma in architecture is a three years course whereas B.arch is a 5 years course.
Diploma in architecture holders have less exposure in design methods and idea generation and termed as diploma holders. Diploma holders can works in offices as assistant or draughtsman under a Architect. Diploma holders don't have the same exposure as degree holders.
Bachelor's in architecture have far more exposure in the field and can work as independent architects. They are termed as architects. They can work in firms an d even develop their own projects. It is a 5 year course.
In terms of salary, degree holders get far moee better pay than diploma holders.

Hope it helps