UNIT-1 Introduction Operating Systems Objectives and Functions: • • • • • Computer = HW + OS + Apps + Users OS serves as interface between HW and ( Apps & Users ) OS provides services for Apps & Users OS manages resources ( Government model, it doesn't produce anything. ) Debates about what is included in the OS - Just the kernel, or everything the vendor ships? Computer-System Organization: Figure - A modern computer system Computer-System Operation: • • • • • Bootstrap program Shared memory between CPU and I/O cards Time slicing for multi-process operation Interrupt handling - clock, HW, SW Implementation of system calls
Figure - Interrupt timeline for a single process doing output Storage Structure: • • • Main memory ( RAM ) o Programs must be loaded into RAM to run. o Instructions and data fetched from RAM into registers. o RAM is volatile o "Medium" size and speed Other electronic ( volatile ) memory is faster, smaller, and more expensive per bit: o Registers o CPU Cache Non-volatile memory ( "permanent" storage ) is slower, larger, and less expensive per bit: o Electronic disks o Magnetic disks o Optical disks o Magnetic Tapes Figure - Storage-device hierarchy
I/O Structure: • Typical operation involves I/O requests, direct memory access ( DMA ), and interrupt handling. Figure - How a modern computer system works Computer-System Architecture: Single-Processor Systems: • • One main CPU which manages the computer and runs user apps. Other specialized processors ( disk controllers, GPUs, etc. ) do not run user apps. Multiprocessor Systems: 1. 2. 3. Increased throughput - Faster execution, but not 100% linear speedup. Economy of scale - Peripherals, disks, memory, shared among processors. Increased reliability o Failure of a CPU slows system, doesn't crash it. o Redundant processing provides system of checks and balances. ( e.g. NASA )
Figure - Symmetric multiprocessing architecture Figure- A dual-core design with two cores placed on the same chip Clustered Systems: • • Independent systems, with shared common storage and connected by a high-speed LAN, working together. Special considerations for access to shared storage are required, ( Distributed lock management ), as are collaboration protocols.