supplementary_lecture_3

supplementary_lecture_3 - cs4411 – Operating Systems...

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Unformatted text preview: cs4411 – Operating Systems Practicum October 14, 2011 Zhiyuan Teo Supplementary lecture 3 • Administrative Information • Machine endianness Today’s lecture • Network header generation • General implementation hints • Discussion • Project 3 updated on Sunday, 9 October. Administrative Information- Please re-download if you used the initial version we released.- Project 3 slides and the instructions have been amended. • Groups may be reshuffled. • Test cases for project 2 are in the project 3 bundle.- Test your implementation to make sure preemption and alarms work.- We will not be grading you on preemption and alarms, but it will be used later on. • Memory is organized as an array of bytes. Machine endianness- Actual ordering of bytes in memory does not change the value stored.- Ordering of bytes does not change final result of arithmetic shift operations. • Machine endianness refers to the physical ordering of bytes within the memory for the multibyte data item. • Multibyte data items such as integers and shorts take up more than 1 byte of storage.- 4 bytes for an integer.- 2 bytes for a short. Machine endianness 12 34 56 78 Big-endian (SPARC, DLX, etc): 32 bitvalue: 0x12345678 de ad 16 bitvalue: 0xdead 78 56 34 12 32 bitvalue: 0x12345678 ad de 16 bitvalue: 0xdead Big-endian (SPARC, DLX, etc): 32 bitvalue: 0x12345678 16 bitvalue: 0xdead Big-endian (SPARC, DLX, etc): 32 bitvalue: 0x12345678 16 bitvalue: 0xdead 16 bitvalue: 0xdead Big-endian (SPARC, DLX, etc): 32 bitvalue: 0x12345678 32 bitvalue: 0x12345678 16 bitvalue: 0xdead 16 bitvalue: 0xdead Big-endian (SPARC, DLX, etc): 32 bitvalue: 0x12345678 Little-endian (Intel, VAX, etc): 32 bitvalue: 0x12345678 16 bitvalue: 0xdead 16 bitvalue: 0xdead Big-endian (SPARC, DLX, etc): 32 bitvalue: 0x12345678 • Humans write in big-endian form; it feels more natural to read. • Short answer: nobody knows....
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This note was uploaded on 12/07/2011 for the course CS 4410 taught by Professor Vollset during the Spring '07 term at Cornell.

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supplementary_lecture_3 - cs4411 – Operating Systems...

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