The IBM-style PC has been around since 1981, but few recognise it as retro.
At school I remember using a flickery, blocky 4 colour display and being expected to draw a decent picture on it. This was around 1984 and I thought it was marvellous!
Later on, I remember using Windows 2.0 on 286 machines and thinking that surely computers couldn't get any better than that.
I particularly enjoyed using the BBC BASIC rom inside RM Nimbus PCs to make little games.