Welcome to the network!
We are working on a wiki for this website, where we can start creating resources such as this one curated by the community. We've 
set the target of finishing up the system by the end of the year, which afaict it is likely we'll meet it!
For now, though, you really can't go wrong with 
Computer Systems: A Programmer's Perspective, which I recommended 
earlier this year. Any textbook on discrete mathematics will likely supplement your learning as well (such as Discrete Mathematics by Kenneth Rosen, or Concrete Mathematics by Donald Knuth); or simply search the topics related to discrete maths and pick some that interest you -- and look for videos and articles related to them. Handmade Hero 
has a good one when it comes to the mathematics used in game dev.