Armenian language

[MOESAN]

on the Net I saw a site where I-E roots was given, with their cognates in different languages and I saw that very often armenian roots was given under 2 forms, one with voiced stops and one with unvoiced or asspired stops:
is there a difference of period (diachronical) or a difference of dialect (geographical)???
Could somebody tell the cause?
thanks beforehand

[MOESAN]

on the Net I saw a site where I-E roots was given, with their cognates in different languages and I saw that very often armenian roots was given under 2 forms, one with voiced stops and one with unvoiced or asspired stops:
is there a difference of period (diachronical) or a difference of dialect (geographical)???
Could somebody tell the cause?
thanks beforehand

nobody can help?