Os concepts 3 I/O and storage Basics
- 1. Operating System Concepts: 3 I/O and Memory Basics Prof Neeraj Bhargava Vaibhav Khanna Department of Computer Science School of Engineering and Systems Sciences Maharishi Dayanand Saraswati University Ajmer
- 2. I/O Structure • After I/O starts, control returns to user program only upon I/O completion – Wait instruction idles the CPU until the next interrupt – Wait loop (contention for memory access) – At most one I/O request is outstanding at a time, no simultaneous I/O processing • After I/O starts, control returns to user program without waiting for I/O completion – System call – request to the OS to allow user to wait for I/O completion – Device-status table contains entry for each I/O device indicating its type, address, and state – OS indexes into I/O device table to determine device status and to modify table entry to include interrupt
- 3. Storage Structure • Main memory – only large storage media that the CPU can access directly – Random access – volatile – random-access memory Dynamic Random-access Memory (DRAM) • Secondary storage – extension of main memory that provides large nonvolatile storage capacity • Hard Disk Drives (HDD) – rigid metal or glass platters covered with magnetic recording material – Disk surface is logically divided into tracks, which are subdivided into sectors – The disk controller determines the logical interaction between the device and the computer • Non-volatile memory (NVM) devices– faster than hard disks, nonvolatile – Various technologies – Becoming more popular as capacity and performance increases, price drops
- 4. Storage Hierarchy • Storage systems organized in hierarchy – Speed – Cost – Volatility • Caching – copying information into faster storage system; main memory can be viewed as a cache for secondary storage • Device Driver for each device controller to manage I/O – Provides uniform interface between controller and kernel
- 6. How a Modern Computer Works A von Neumann architecture
- 7. Direct Memory Access Structure • Used for high-speed I/O devices able to transmit information at close to memory speeds • Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention • Only one interrupt is generated per block, rather than the one interrupt per byte
- 8. Computer-System Architecture • Most systems use a single general-purpose processor – Most systems have special-purpose processors as well • Multiprocessors systems growing in use and importance – Also known as parallel systems, tightly-coupled systems – Advantages include: 1. Increased throughput 2. Economy of scale 3. Increased reliability – graceful degradation or fault tolerance – Two types: 1. Asymmetric Multiprocessing – each processor is assigned a specie task. 2. Symmetric Multiprocessing – each processor performs all tasks
- 10. A Dual-Core Design • Multi-chip and multicore • Systems containing all chips – Chassis containing multiple separate systems
- 11. Non-Uniform Memory Access System
- 12. Clustered Systems • Like multiprocessor systems, but multiple systems working together – Usually sharing storage via a storage-area network (SAN) – Provides a high-availability service which survives failures • Asymmetric clustering has one machine in hot-standby mode • Symmetric clustering has multiple nodes running applications, monitoring each other – Some clusters are for high-performance computing (HPC) • Applications must be written to use parallelization – Some have distributed lock manager (DLM) to avoid conflicting operations