History of Computer Systems

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Application Libraries

User space/level Kernel space/level

Portable OS Layer Machine-dependent layer

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Written by programmer Compiled by programmer Uses function calls

Portable OS Layer Machine-dependent layer

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Application Libraries (e.g., stdio.h)

Portable OS Layer

Provided, pre-compiled Defined in headers Input to linker (compiler) Invoked like functions May be “resolved” when program is loaded

Machine-dependent layer +

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Application Libraries

Portable OS Layer

system calls (read, open..) All “high-level” code

Machine-dependent layer 1

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Application Libraries

Portable OS Layer Machine-dependent layer

Bootstrap System initialization Interrupt and exception I/O device driver Memory management Kernel/user mode switching Processor management


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Exception/Interrupt/Fault

kernel

user Set user mode

Privileged instructions can be executed only in kernel mode.