The programmers frequently had to crawl inside the computer to find connection problems, tubes, and defective components. At its most reliable, it rarely functioned more than a day without being down for repairs. With a cost of over a million in 1940s dollars, down time was a big deal.
Reprogramming ENIAC was generally a two week process. It literally had to be rewired. “Function panels” that had 1200 ten position switches had to be properly setup. The operation of ENIAC would not have been possible without a group of brilliant and capable programming engineers referred to as “computers” at the time. The primary programmers for the ENIAC were all women, Kay McNulty, Betty Jennings, Betty Snyder, Marylyn Wescoff, Fran Bilas, and Ruth Lichterman.
The programmers had to determine how to setup ENIAC in order to solve specific functions such as artillery trajectory tables for the Army or simulations for thermonuclear bombs. These early programmers did not receive the recognition they justly deserved for more than 50 years. They were selected due to their position as “computers’. One of the few technical positions women were allowed to hold. Their expertise and contributions were not considered important. The “programmers” even invited to the 50th anniversary celebration of ENIAC. The hardware was considered the primary innovation and not the intricate programming, operation, and program design performed by the “computers”. We now know that hardware is just a pile of parts without the profession of programmers.