The National Library of Medicine has been collecting and organizing citations of biomedical literature since its founding. For more on the history of these systems, see the articles below.
Image: IBM magnetic tape drives of the IBM 370/155 with NLM staff
Source: The development of the Medical Literature Analysis and Retrieval System (MEDLARS). Journal of the Medical Library Association, 95(4), 416–425. http://doi.org/10.3163/1536-5050.95.4.416