CS 25000 Lecture Notes - Lecture 12: Program Counter, Interrupt, Opcode
20 Mar 2017
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Document Summary
High-level languages featuring strong abstraction from the details of the computer; portable; programmer productivity. Portable among different computers with some effort; some machine-dependent features are visible; performance. Assembly languages: a distinct one for each computer, hardware dependence, just a few abstractions. 32- & 64- bit strings 32- & 64- bit strings strings strings. Assembly is two-pass, to computer offsets: many offset values are positive. If-then-else skips ahead in a program: skip ahead to else when condition =false, or execute then and skip over else. Instructions ahead in a program are located at higher numbered memory addresses. Initial pass of assembler eventually determines memory addresses of all labels, even those are forward references, recording progress in a symbol table. Lecture 12: position-dependent machine code can have it absolute addresses adjusted so that references remain correct when the code is relocated by using a relocation table, assembly supports defining data items using directives, examples:
