COP 4610 Introduction to Operating Systems

Chapter 1 - Introduction OS - Layer between the hardware and user programs (Figure 1.1) OS - The ultimate API OS - First program that runs when the computer boots up OS - Program that is always running OS - Typically only one instance/machine

An OS functions as a resource manager and an implementer of virtual computers As a resource manager, the OS handles hardware, typically consisting of: –Processor –Memory –I/O controllers –Disk devices –Other I/O devices Abstract H/W diagram: Figure 1.2

Resource management by an OS involves: –Transforming a physical resource into an instance of a virtual resource (e.g., a printer) –Multiplexing between different instances of a virtual resource when there’s only one physical resource (e.g., use of SPOOLing disk files for virtual printers) –TDM (time division multiplexing) vs SDM (space division multiplexing); some resources make sense to TDM (printer); others SDM (disk) –Scheduling resources between programs

An OS creates a virtual computer for each program, with each it’s own: –Process(es) (TDM) –Address space(s) (SDM) –Disk objects/file system (SDM) The illusion is complete: Figure 1.3 Each virtual component has it’s own rules: –Figure 1.4: Virtual Processor Some native real processor instructions are masked; new “instructions” are added (aka system calls) P virtual = P physical - {Priv. Instr} + {Useful Instr}

Each virtual component has it’s own rules: –Figure 1.4: Virtual Processor (continued) Separation of instruction privileges decided (hopefully!) by hardware states: system and user Protected instructions are those which allow indiscriminate access to the hardware (address all of memory, access any I/O device, etc.) –Figure 1.5: Virtual Primary Memory Create illusion that each program has it’s own private memory starting at address 0 –Figure 1.6: Virtual I/O Create illusion that each program has it’s own set of hardware devices

–Figure 1.7:Virtual Secondary Memory Create illusion each program has it’s own private disk drive/file system