Saturday, December 14, 2013

i/o


          

System Characteristics

  • The Dependability is important especially for storage devices.
  • Performance measures
  1. Latency(response time)
  2. throughput(bandwidth)
  3. Desktops and embedded systems for response time and diversity of device
  4. Servers 

Dependability 

The system dependability is and to plan the time and resources needed to complete the case.

Interconnecting Component

  • Must have interconnections between CPU, memory, I/O controllers.
  • Bus: shared communication channel
         ◦Parallel set of wires for data and synchronization of data transfer
         ◦Can become a bottleneck
  • Performance limited by physical factors                                                                                             
  1. Wire length
  2.  number of connections
  • More recent alternative: high-speed serial connections with switches
          ◦Like networks

Bus Types
  • Processor-Memory buses must short, high speed and design is matched to memory organization
  • I/O buses
             ◦Longer, allowing multiple connections
             ◦Specified by standards for interoperability
             ◦Connect to processor-memory bus through a bridge




Bus Synchronization

  • A bus can be classified as synchronous or asynchronous.
    • The time for any transaction over a synchronous bus is known in advance. In accepting and/or generating information over the bus, devices take the transaction time into account.
    • Asynchronous bus, on the other hand, depends on the availability of data and the readiness of devices to initiate bus transactions.

  • In a single bus multiprocessor system, bus arbitration is required in order to resolve the bus contention that takes place when more than one processor competes to access the bus.
    • The bus arbitration logic decides, using a certain priority scheme, which processor will be granted access to the bus during a certain time interval (bus master).
      • Random priority,
      • simple rotating priority; after each arbitration cycle all priority levels are reduced one place, with the lowest priority processor taking the highest priority.
      • Equal priority; when two or more requests are made, there is equal chance of any one request being processed.
      • Least Recently Used (LRU) priority; the highest priority is given to the processor that has not used the bus for the longest time.
    • The process of passing bus master ship from one processor to another is called handshaking and requires the use of two control signals: bus request and bus grant.
      • the first indicates that a given processor is requesting master ship of the bus,
      • the second indicates that bus master ship is granted.
      • a third signal, called bus busy, is usually used to indicate whether or not the bus is currently being used.
                                                                                   


                                                                                                            Published by:
                                                                          SITI NURHASTINI BINTI ROSALI
                                                                              (B031310320)









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