CSC369 All Lecture Notes.docx

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Angela Demke Brown

Operating Systems Lecture NotesOperating Systems Lecture 2Add a mode bit to the hardware and designate some instructions as privileged instructionsPrivileged instructionsoperationsSetting mode bitDisabling interrupts Writing to device registers Performing DMA Direct Memory Access Halting the CPUNon privileged instructionsoperationsEnabling interrupts InterruptsDefn A hardware signal that causes the CPU to jump to a predefined instructions called the interrupt handler 1OS fills in Interrupt Table at boot time2CPU execution loop Fetch instruction at PCDecode instrexecute instrLOOP3Interrupt occurs signal form hardware4CPU changes mode disables interrupts5Interrupted PC value is saved6IDTRinterrupt number is used to set PC to start interrupt handler7Execution continues saves additional state as first stepBootstrapping Hardware stores small program in nonvolatile memory BIOSBasic Input Output System Knows how to access simple hardware devices Disk keyboard display When power is first supplied this program starts executing Hardware starts in system mode so OS code can execute immediatelyOS initialization Initialize internal data structures machine dependant operations are typicallydone first Create first process init Switch mode to user and start running first process Wait for something to happen something always starts with an interrupt Every modern computer is a multiprocessor since it has hardware with miniCPUsFirst 512 bytes of physical memory are reserved for exeception vector code Interruption Table which is filled by OSInitial stack pointer is set to point to top of physical memory Operating Systems Lecture 3 The process is the OS abstraction for executionAKA a job or task or a sequence processDefinition a process is a program in execution The OS manages processes by keeping track of their state Different events cause changes to a process state which the OS must recordimplementNEWAdmitREADYDispatch RUNNINGReleaseEXIT Timeout Event Occurs Event wait BLOCKED Process Control Block generally includesa process state ready running blocked program counter address of the next instructionCPU registers must be saved at an interruptCPU scheduling information Threads execute in the kernel in os161 and a process is the execution of code at user levelProcess can have multiple threads and all threads belong to a process Threads have their own information different from each other and the information they share is the one that belongs to the process they belong toHow does the OS keep track of processes
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