When I was a kid (1980s), I remember we had a couple of books on assembly and “machine language”. I occasionally try to find them online, but I’m not sure what to look for. I think the covers were blue. I wish I had read them back then.
I’m not sure if this was one of them, but I stumbled on it while searching around:
There’s another one here that might interest people:
Hmm, so by machine language these books seem to mean assembly language, in this case for the 6502 processor. (I thought machine language referred to just the 1s and 0s, but evidently that’s not always the case – shows what I know!)
Looking at these made me wonder about the book “The Art of Assembly Language” from No Starch Press. Tracking down that book, I see that the author also wrote a book on 6502 assembly, and he’s posted a pdf of this on his website.
(Also, holy moly does he have some ugly pages on his website! 
They must be pretty old – looks like something I would have made in the 90s, but with even worse colors. 
)
Edit: The cover on the book is awesome though. Looks like the cover of a 70s sci-fi novel.
That’s actually why I had been searching for the book. I remember two books: one on assembly and one on “machine language”. I remember browsing through the books but never read them. I was wondering what “machine language” was and why it was a separate book from the assembly one — I thought it might have been about how to code in raw hexadecimal numbers or something interesting like that. 
Maybe they were both on assembly and just used different terms. Or maybe it’s a distorted memory and there was one on “machine language” and one on DOS or something else.
Oh, I see. Your thinking is probably correct about the two books. Didn’t people used to only program in machine code? For example, computers like the Altair just have a row of toggle switches. I thought that was for setting every bit for each processor cycle.
Doing an image search on 6502 Machine Language Book sure turns up a lot of fun old book covers. 
I don’t see the book in Google Images, but I was probably only about 12, so the memories are faint. I think it was dark blue with white text, and squarish.
While looking at the images, I stumbled on a collection of related titles here:
I wish I had read books like that back in those days. I bought a used Commodore 64 in high school (for $100 if I remember correctly), but I did little more than play games with it. I was interested in learning programming, but didn’t really know how to go about doing so. I also wasn’t very motivated at all – just sort of drifting through life. I did eventually take a BASIC class in high school though, which was fun.