Vimshottari Dasa and Ashtottari Dasa

[gnanpipasu]

Respected Members,
What is the difference between
Vimshottari Dasa, Ashtottari Dasa, Mahadasa & Antar Dasa
As I look at my birth charts I have different dasas running as per Vimshottari Dasa and Ashtottari Dasa.

Can some one please explain in short and give me good reference of books I can read to understand.

Thanks

[revribhav]

It is said that the Ashtottari dasa may be used, when a question of longevity is needed.
In order to
use Ashtottari dasa for a given horoscope, however, the following
should apply:

a. Birth in the daytime during the waning Moon phase;
b. Birth in the nighttime, during the waxing Moon phase; and,
c. Rahu be in a kendra or trikona house from
the Lagna lord .