Berkeley CSUA MOTD:Entry 19624
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2025/04/03 [General] UID:1000 Activity:popular
4/3     

2000/11/1 [Computer/HW/Memory, Computer/HW/CPU] UID:19624 Activity:low
10/31   When one CPU on a dual Pentium II machine executes an instruction that
        writes to memory, and later the other CPU executes an instruction that
        reads the same memory, how does the second CPU get the correct value
        from the first CPU's cache?  Thanks.
        \_ Many cheepo/low end systems use a cache coherent protocol called
           MESI (modify, exclusive, shared, invalid). This works fine under
           smaller systems that can do bus snooping. But for much larger
           systems (like 512 processor systems) they use a more sophisticated
           directory lookup structure. -jeff
           \_ For more information about MESI on intel processors, see
              http://developer.intel.com/design/pentiumii/manuals/24319202.pdf
              chapter 9, especially section 9.4.
        \_ Distinction between cache and system memory.  Dirty|clean bits.
           \_ Do you mean the two CPUs share the same caches instead of having
              separate caches?
              \_ No, each Pentium has its own cache.
              \_ They probably run in separate processes, separate
                 address spaces.
                 \_ You're probably a total fucking idiot.
        \_ I believe that Hennessey and Patterson (not to be confused with
           Patterson and Hennessey) discusses multiprocessor machines.  You
           you might want to check it out for a detailed explantion. -dans
           \_ Just an aside, that naming convention is only used in Berkeley.
                                        - current grad student somewhere else
                \_ Uh, that is the author order on the books themselves.
                   Although I think Culler's parallel architectures book
                   does a better job discussing cache coherance. -nweaver
        \_ Thanks for all the answers.  I had a lousy prof for 152 (last name
           started with R and was very long, don't remember exactly), and it
           has been 7 years.
2025/04/03 [General] UID:1000 Activity:popular
4/3     

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