Census 2000 (sf1 sf2 sf3 sf4)

Following information explains the difference between Census 2000 summary files 1 thru 4 (sf1 thru sf4)

It is quoted from http://www.ncsu.edu/woodlands/current_pdfs/teleconf_data_sources.pdf 

SUMMARY FILE DESCRIPTION

SF1 (Summary File 1)

This is a 100% sample of the whole population of the United States, down to the Census Block level. It has information on age, sex, race, Hispanic/Latino origin, household relationship, whether residence is owned or rented.

SF2 (Summary File 2)

This is a 100% sample of the whole population of the United States, down to the Census Block level. It has the same information as SF1, but is organized by race or tribe. No tables are available for geographic areas having a population of less than 100.

SF3 (Summary File 3)

This is a 1-in-6 sample of the population, down to the Census Block Group level (less resolution than SF1 and SF2). It presents detailed population and housing data (such as place of birth, education, employment status, income, value of housing unit).

SF4 (Summary File 4)

This is a 1-in 6 sample of the population, down to the Census tract level (less resolution than SF1, SF2 and SF3). It has the same information as SF3, but is organized by race or tribe.