Poor explanations such as this annoy me: "By replacing the initial R with an E on the first eight registers, it is possible to access the lower 32 bits (EAX fo

Poor explanations such as this annoy me: "By replacing the initial R with an E on the first eight registers, it is possible to access the lower 32 bits (EAX for RAX). Similarly, for RAX, RBX, RCX, and RDX, access to the lower 16 bits is possible by removing the initial R (AX for RAX), and the lower byte of the these by switching the X for L (AL for AX), and the higher byte of the low 16 bits using an H (AH for AX)" It makes learning more difficult. Something like this would be way better: "Specific parts of the registers can be accessed separately from the rest of the register, within strict limitations dictated by the format of instructions. These register-parts are given easy-to-remember names. The lower 32 bits of the first eight registers can be accessed as EAX, EBX, ECX, EDX, EBP, ESI, EDI and ESP. The lower 16 bits of registers EAX, EBX, ECX and EDX can also be accessed as AX, BX, CX and DX. Finally, both the lower and the second-lower bytes of registers EAX, EBX, ECX, EDX can be separately accessed as AH, AL, BH, BL, CH, CL, DH and DL, with AL/BL/CL/DL being the lowest-order byte and AH/BH/CH/DH being the other one. Knowing what things are due to what part of the model, and what parts are conventions, is a big part of understanding, which is just building a good model of the architecture in your mind. It took me years to understand two's complement arithmetic, and the key missing point was that it is just a convention. A convention with great practical advantages, but a convention anyway.