It was a long time ago, but when I worked at GEC Avionics I came across some old circuit boards in a cupboard. When I asked what they were, I was told they were circuit boards from Concordes avionics, but were at that time obsolete. The boards I found were basically 2nd generation computer components. Such machines used discrete components, like transistors, very little more complicated than that, and were probably analogue computers.
The replacements were 3rd generation technology, i.e. all the discrete electronics were replaced with with integrated circuits, like op-amps, discrete logic chips and likely the odd early microcontroller or even an 8-bit processor. The change reduced the size of the avionics, plus its power requirement. Reliability no doubt was improved as well, and being digital were also going to be easier to setup and calibrate.
This was in 1986, which if you think back was when 8-bit home computers were new and expensive toys. Programming and design work was carried out on huge Vax mainframes. We had a couple of BBC Micros that we were tinkering with to see if it would be possible to ship software updates for Airbus via a modem link, rather than flying people back and fore with EPROMS in their baggage.