Although an 8-bit CPU, I've always thought the PEP8 simulator [1] (Warford, Pepperdine) was nice in that it is a visual simulation of the CPU: [1] http://www.c

Although an 8-bit CPU, I've always thought the PEP8 simulator [1] (Warford, Pepperdine) was nice in that it is a visual simulation of the CPU: [1] http://www.cslab.pepperdine.edu/warford/CSUploads/Pep8CPUPaper.pdf http://www.cslab.pepperdine.edu/warford/CSUploads/Pep8CPUPap... EDIT: and if you want an absolutely wonderful series of lectures on computer systems, CPU architecture, assembly, etc., checkout Warfords free course on iTunesU [2] [2] https://itunes.apple.com/us/course/computer-systems/id546468937 https://itunes.apple.com/us/course/computer-systems/id546468...