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  2. 2. Input Output Buffering There is a speed mismatch between I/Odevices and CPU. This leads to inefficiency in processes beingcompleted. To increase the efficiency, it may beconvenient to perform input transfers inadvance of requests being made and toperform output transfers some time after therequest is made. This technique is known as buffering
  3. 3. Input Output Buffering In discussing the various approaches tobuffering, it is sometimes important to makea distinction between two types of I/Odevices: Block-oriented devices store information in blocksthat are usually of fixed size and transfers aremade one block at a time for example disk,tape Stream-oriented devices transfer data in and outas a stream of bytes, with no block structure forexample terminals, printers, communicationsport, mouse.
  4. 4. What is single buffer ?? Operating system assigns a buffer in mainmemory for an I/O request Example when a user process issues an I/Orequest, the operating system assigns a buffer inthe system portion of main memory to the operation
  5. 5. Single buffer process The simplest type of buffering is single buffering. When a user process issues and I/O request, theoperating system assigns a buffer in the systemportion of main memory to the operation. For block-oriented devices, the single bufferingscheme can be described as follows: Inputtransfers are made to the system buffer. When the transfer is complete, the process movesthe block into user space and immediatelyrequests another block.
  6. 6.  For stream oriented I/O, the single bufferingscheme can be used in a line- at- a time Fashionor a byte-at-a-time fashion. In line-at-a-time fashion user input and outputto the terminal is one line at a time. For eg.Scroll-mode terminals, line printer. Suppose thatT is required to input one block andthat C is the computation time. single buffer : you read and write on the samebuffer, can be messy if both reading and writingtake place at the same time.Single buffer process
  7. 7. What is double buffer ? Two buffers are used for the I/O operation .It’salso the process uses the content of one bufferwhile the I/O device uses the other. Double-buffering possibly sounds harder than itactually is.
  8. 8. ADVANTAGES The user does not see every pixel modification(so if the same pixel gets modified 5 times, theuser will only see the last one).This helpspreventing flickering (or screen flashes). Double-buffering usually takes care of artifactsyou or the user might be experiencing. Writing to video memory is only performedonce, on the buffer swap, instead of repeatedlyfor every pixel of which some might beoverlapped later and might be invisible.
  9. 9. DISADVANTAGES Even though double-bufferingis useful, it also has negativecharacteristics. Each is listedwith an explanation and apossible solution.
  11. 11. Circular Buffering When more than 2 buffers are used-- each individual buffer is one unit in the circularbuffer… Is used when…--double buffering may be not enough if processperform rapid bursts of I/O… Therefore, this type of buffering is needed forkeeping up with the process
  12. 12. Circular buffer of a processused for data transfer between 2 processes.Producer process: place item into circular bufferConsumer process: remove the itemVariable capacity of circular buffer accommodatetime ≠ producer and consumer process…--can execute faster than the other queue that hold avariable amount of data since…A fixed size block of memory is allocated just oncefrom memory management and then reused.
  13. 13. -- often is used to decouple 2 processes thatoperate at different speeds…-> fast producer process:--- can “burst” data into buffer and thencontinue with its processing-> slower consumer process:--- can read the data with its own rate withoutsynchronizing and slowing the producer.Circular buffer of a process
  14. 14. -the average rate, over time, of bothproducer and consumer process must besame to avoid over or underflow ofcondition of the circular buffering(“Synchronize Mode “ of operation)Circular buffer of a process
  15. 15. --- 2 methods can avoid data lossin synchronize mode--- 2 methods can avoid data loss in synchronize mode:a) Calling blocking method: calling thread to block until the Circular buffer hasthe requested number of items.b) WaterMark method: fire an event when the number of items in thecircular buffer reaches a preset level…~~ eliminating wasting processing time due toprocess block.