Computers in Spaceflight - The NASA Experience: http://history.nasa.gov/computers/contents.html
Digital Apollo, by David A. Mindell -
The Apollo Guidance Computer: Architecture and Operation by Frank O'Brien - http://www.amazon.co.uk/The-Apollo-Guidance-Computer-Archite...
I'd also recommend Turing's Cathedral by George Dyson and The Soul of a New Machine by Tracy Kidder.
Many early IT systems used special-purpose hardware, and boundary between the software and hardware development wasn't as clear as it is now. For this reason, I think, many surveys tend to emphasise the hardware aspect.