Form G-325a (Biographic Information) is a form used to submit biographical information on an applicant in conjunction with an application for a USCIS benefit (such as a visa, or to adjust ones status). The form is made up of four sheets, each containing the same information. The four sheets are marked A through D, and each sheet is used by a different area in the application process.
This form is only filed with another application.
The G-325 biographic information form is one that causes much in the way of unnecessary anguish. Experience notes that the form is not all that important -- it is rarely even examined by the government officials in the process! As a general rule, it pays to remember that the form has not had a substantive revision since Dwight Eisenhower was president of the United States.
Before the advent of printed forms, the G-325 was issued in carbon packs. The only difference between the G-325 and the G-325A form was that the G-325 was a two page package and the G-325A had four pages. Both forms have now been revised to just one page -- in other words, other than the "A" notation, there is no difference between the forms and they are interchangeable.
A frequently asked question is in regards to the item asking for the reason for its submission. In the case of a spousal I-130, one can check the box regarding "residence," "other" with a notation of "I-130," or even leaving the matter blank. The G-325 used to be used in many more applications than today. For example, it used to be required for naturalization applications. Even though the check-box for "naturalization" is obsolete, it is a vestigial part of the form that has survived many minor revisions.
As a general rule, the information provided on the G-325 should be correct. However, it is not fatal if the information is incomplete. For example, the actual street addresses of past residences need not be provided -- the city is often sufficient; exact dates need not be provided -- month and year will suffice. If one does not know what month, provide at least the year. If one had a series of addresses over a period of time in a location, a notation such as "various addresses, Cornwall, UK" will suffice.
In regards to I-130's, it should be remembered that the G-325's are required for spousal petitions only. The G-325 is not required for petitions on behalf of step-children or parents.
Further point -- if a "combined" I-130/485 package is filed, the alien need submit only one I-130, not two.
General Rule -- do not fret over the form; answer the items as best you can.