Purpose: This paper identifies the roles and place of a preprint server, arXiv, in scholarly communication by analyzing all papers submitted to arXiv up to 2007. Methods: In order to clarify 1) the growth in the annual and total number of submitted papers, 2) the percentage of papers in arXiv subsequently published in scholarly journals and their publication information, and 3) differences of years between submission to arXiv and publication in journals (i.e., immediacy), all 449,071 papers submitted to arXiv between 1991 and 2007 were analyzed by examining the~following data for each paper: 1) ID, 2) "journal-ref" which is bibliographic references of publications in which the submitted paper appeared, and 3) subject categories. Results: The main findings are as follows. 1) For 17 years, the overall annual and total number of submitted papers continued to increase, especially in astrophysics, condensed matter, and mathematics. However, the rate of increase differs between disciplines. 2) The percentage of papers in arXiv subsequently published in scholarly journals was 47.1% on average, indicating that about half of them were published. The journal-ref addition rate was much higher in physics and theoretical subject categories than in mathematics and computer science. Papers published in core journals in physics and astronomy, such as the Physical Review series and Astronomical Journal, accounted for almost half of all papers submitted to arXiv. 3) Whereas most papers submitted in high energy physics (HEP) categories can be accessed before publication, some subject categories, in contrast to HEP, generally provide access to older scholarly articles. In conclusion, arXiv is now simultaneously serving two roles: as a preprint server of journal articles and as a digital archive of scholarly articles in general. [ABSTRACT FROM AUTHOR]