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UNIX buffer management

UNIX buffer management one of the critical component of the operating system<br>

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UNIX buffer management

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  1. UNIX Buffer Managemen Prepared By:Ayan Banerjee Master of Technology (M.tech)-Computer Science & Engineering UNIX Buffer Management UNIX Buffer Management Operating System – I/O Subsystem Buffer Cache, Free List, Hash Queues

  2. Introduction • UNIX buffer management is a critical component of the operating system • It handles efficient transfer of data between disk and memory and vice-versa • Reduces direct disk access by caching disk blocks • Improves overall system performance and throughput and increase system efficiency

  3. What is a Buffer? • A buffer is a temporary storage area in main memory • Used during data transfer between CPU and I/O devices • Helps handle speed mismatch between disk and processor • Commonly used in file systems and device drivers

  4. Need for Buffer Management • Disk access time is much slower than memory access • Frequent disk I/O degrades system performance • Buffers reduce redundant read/write operations • Enables efficient multitasking in UNIX

  5. UNIX Buffer Cache • Buffer cache is a pool of buffers in RAM • Each buffer stores one disk block • Shared among all processes in the system • Avoids repeated disk reads for same data

  6. UNIX Buffer Cache • Buffer cache is a pool of buffers in RAM • Each buffer stores one disk block • Shared among all processes in the system • Avoids repeated disk reads for same data

  7. Buffer States • Locked (Busy): buffer currently in use • Valid: buffer contains correct data • Delayed Write: data modified but not written to disk • States ensure synchronization and data consistency

  8. Free List • Free list holds buffers not currently in use • Implemented as a circular doubly linked list • Buffers are reused efficiently • Helps in fast buffer allocation

  9. Hash Queues • Hash queues provide fast buffer lookup • Hash function uses device number and block number • Each hash queue is a linked list of buffers • Reduces buffer search time significantly

  10. Buffer Allocation Algorithm • Check hash queue for requested block • If buffer exists and is free → allocate it • If buffer is busy → process waits • If block not present → take buffer from free list

  11. Delayed Write Mechanism • Modified buffers are not written immediately • Buffer marked as delayed write • Improves performance by reducing disk writes • Disk write occurs during replacement or sync

  12. Read Operation in UNIX • Process makes a read system call • Kernel checks buffer cache first • If block present → data copied to user space • If not → block read from disk into buffer

  13. Write Operation in UNIX • Data written to buffer cache initially • Buffer marked as delayed write • Process does not wait for disk write • Kernel writes data to disk late

  14. Advantages of Buffer Management • Minimizes disk I/O operations • Improves system response time • Supports efficient multi-process access • Enhances UNIX file system performance

  15. Conclusion • UNIX buffer management is essential for OS efficiency • Combines buffer cache, hash queues, and free list • Ensures fast, consistent, and reliable I/O • Forms the backbone of UNIX file systems

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