Way back in 1977 or '78, my dad worked for RCA. When they decided to offer a hobby computer (as a kit), he picked one up. At that time, hobby computers came with a hex keypad and you entered two digits (one byte) directly into memory. The manual included a very simple language for writing games along with half a dozen examples such as a clone of Pong..
The processor was something called an 1802, also called a COSMAC, while the computer as a whole was called a VIP. It had a very simple instruction set, so I sat down with some graph paper and figured out what each instruction was doing.
Of course, that's a lot simpler when you only have 2K of RAM (and that was expanded from the original 512 bytes) as opposed to today's multi gigabytes, no way to do that now.