Greeting to everyone, I just stumbled on this group for some reason or other, so this is my first posting.
Let me start saying that I was one of those early games programmers, back in 1980 I had my first title released on an 8bit home computers and several more after this time.
So firstly I will only comment on my own experience of 10years+ games programming, that pretty much all titles of this era are written in assembly language, which naturally translates into what's known as machine code. There quite likely is some early titles of days which would not have such luxury and would be written on paper and hand assembled into hex, and thus made into a binary form.
The idea of C didn't exist, and any high-level language would not really cut it in the world of small memory, large video frame buffers, and CPU with simple instruction sets.
Consoles devices just didn't have a kernel as such, so you had to do everything from nothing, with reference documents by manufacturers, after you agreed with a DNA.
Home computers of the time had a form of Basic pretty much a common thing, and many titles simpler in nature text adventure etc could well be done this way.
The original idea about just slotting in graphics never happened, there was no template to work with, and that if you were lucky, there was some kind of reference material.
I put my efforts into 6502, 65c02 and some 65816 (ie SNES). A lot of graphics tools and utilities, such as a map design, would tend to be written for the project in hand. Whilst later some useful stuff appeared on the PC in shape of Delux Paint (DP) let's face it a mouse is easier to use to draw with than a joystick!
A lot of the consoles has specialist and expensive developments system, which would be a loan item, or sometimes part of a deal with a project for a contract of development, as the studios started to make cash. A lot of studios to save contractor costs would build in-house development teams, with the potential of being cheaper to produce titles. (not always for the better)
Myself I used cross development on some home computers for a target device, in case of the C64 computer I re-programmed the BIOS and added my own keyboard keys to jump to a parallel port download from another home computer holding all the assets. Cross development what we called it.
I'd be happy if I get more spare time to answer any other questions anyone would like to pose. As it's a Sunday, and my Son is getting tired of a little midday sleep!
regards to all.