GENERAL CONSIDERATIONS INVOLVED IN THE DESIGN OF FILE ORGANIZATIONS FOR INFORMATION RETRIEVAL SYSTEMS ARE DISCUSSED. THE QUESTION OF INVERTED FILE AND SERIAL FILE SEARCHING ON MAGNETIC TAPE IS REVIEWED. BASED ON FORMULAS CONCERNING INDEX TERM USAGE, IT IS SHOWN FOR A SPECIFIC COLLECTION THAT SEARCHING THE SERIAL FILE IS MORE EFFICIENT THAN SEARCHING THE INVERTED FILE. THIS RESULT IS THEN GENERALIZED TO LARGE COLLECTIONS. TWO EXISTING FILE ORGANIZATIONS SERVE AS ILLUSTRATIONS. DISC STORAGE DEVICES ARE DISCUSSED TOGETHER WITH DISC ORGANIZATION OF SPECIFIC FILES. IT IS CONCLUDED THAT THE USE OF AN INVERTED FILE SCHEME IS MOST APPLICABLE ON A DISC. THIS DOCUMENT IS A THESIS PRESENTED TO THE GRADUATE FACULTY OF LEHIGH UNIVERSITY IN CANDIDACY FOR THE DEGREE OF MASTER OF SCIENCE IN INFORMATION SCIENCE. IT IS AVAILABLE AS PB-173-218 FROM THE CLEARINGHOUSE FOR FEDERAL SCIENTIFIC AND TECHNICAL INFORMATION, SPRINGFIELD, VIRGINIA 22151, $3.00 FOR HARD COPY, $.65 FOR MICROFICHE, 50 PAGES. (AUTHOR)