New devices are easyly attached to a computer system

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# New devices are easyly attached to a computer system without waiting for the operating-system vendor to develop support code.
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Introduction to OS 15 29 I/O Structure (cont’d) ! The interrupt-driven I/O is fine for moving small amounts of data. " But can produce high overhead when used for bulk data movement (e.g., disk I/O). ! Direct memory access (DMA) is used to solve this problem. " First set up buffers, pointers (to memory block) , and counters for the I/O device. " The device controller transfer the entire block of data directly to/from its buffer to/from memory, with no intervention by the CPU. " One interrupt for each block access, rather than per byte. 30 I/O Structure (cont’d)
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Introduction to OS 16 31 I/O Structure (cont’d) 32 Computer System Architecture ! Computer systems can be categorized according to the number of general-purpose processors used . ! Single-processor systems : " There is one main CPU capable of executing a general- purpose instruction set. " Almost all systems have other special-purpose processors as well. # Device-specific processors (e.g., graphics controllers). # Do not run user processes and are managed by the operating system. # Relieve the overhead of the main CPU.
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Introduction to OS 17 33 Computer System Architecture (cont’d) ! Multiprocessor Systems : " As known as parallel systems . " Have two or more processors in close communication. " Share the same computation resources (memory, bus, …). " Main advantages: # Increased throughput : $ We expect to get more work done in less time. $ The speed-up ratio with N processors is not N , however; rather, it is less than N . $ A certain amount of overhead is incurred in keeping all the parts working correctly. 34 Computer System Architecture (cont’d) " Main advantages: # Economy of scale : $ Cost less than equivalent multiple single-processor systems, because they share computation resources. % Store data on the same disk vs. many copies of the data. # Increased reliability : $ If functions can be distributed properly among several processors, then the failure of one processor will not halt the system, only slow it down.
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Introduction to OS 18 35 Computer System Architecture (cont’d) ! The multiple-processor systems in use today are of two types: " Asymmetric multiprocessing (master-slave relationship): # Each processor is assigned a specific task. # A master process controls the system. # The master processor schedules and allocates work to the slave processors. " Symmetric multiprocessing (SMP) : # All processors are peers , performs all tasks within the operating system. # Operating system must be written carefully to avoid unbalanced resource arrangement . $ One processor may be sitting idle while another is overloaded. # Virtually all modern operating systems (windows, Mac OSX, Linux) now provide support for SMP. 36 Computer System Architecture (cont’d) ! A recent trend in CPU design is to include multiple compute core on a single chip. " In essence, these are multiprocessor chips.
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  • Spring '12
  • GwangS.Jung
  • OS, main memory

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