You had to know things and keep them in your head, and have a pile of text books otherwise! Plus no normal app had access to gigabytes of storage, and indeed that was a vast amount for many years more[1]. Skills learnt then in terms of memory and CPU efficiency are still valuable now, though your typical smartphone is more powerful than the supercomputer replacements I used to look after for an oil company...

[1] https://www.amazon.co.uk/Managing-Gigabytes-Compressing-Inde... (1999)