Before that time, ‘computing’ was considered largely ‘women's work’, along with other clerical tasks like filing and word processing. I'm fond of this photo of a room full of computers, taken sometime between between 1909 and 1932: http://www.loc.gov/pictures/item/90710989/
The "computers" being the people, the machines are computing machines - or more likely here, merely calculating machines. At least that's the early usage in the UK.
