Flashcards
OS
Cards in this deck (15)
- 1Explain multi-programming and time-share systems, and state their common purpose.Multiprogramming allows several jobs to be in memory at the same time. Time sharing systems extend multiprogramming by allowing CPU scheduling algorithms to switch between jobs so rapidly that they appear to be concurrently run. Both systems ensure the CPU always has a job to execute.
- 2Identify the two hardware modes that prevent user interference with system operation, and explain how each does so.Kernel mode: CPU can execute every instruction and has complete access to hardware.
User mode: permits a subset of instructions and hardware features, specifically keeping the user from I/O instructions and altering the memory. - 3CPU's contain ____ inside to hold ______ and temporary ____.CPUs contain registers inside to hold variables and temporary results.
- 4Define a register, and define three examples of one as well.A register is a storage space of 8 or 32 bits. Examples:
general-purpose registers-store variables and temporary results
program counter-stores the memory address of the next instruction to be fetched
stack pointer-points to the top of the current stack in memory - 5The stack contains one ____ for each procedure to be entered. _____s hold input parameters, local variables, and temporary results not kept in registers.The stack contains one frame for each procedure to be entered. Stack frames hold input parameters, local variables, and temporary results not kept in registers.
- 6Define system calls and give some examples of them.System calls are routines written in C/C++ that interface among the OS's services, and between these services and the user's I/O. Examples: open file, possible error(print, abort), create file (file exists, rewrite/rename...), close files
- 7What does the API specify, and to whom?The API specifies a set of functions available to the application programmer, including the parameters passed to each function and the return values the programmer can expect.
- 8How does a programmer access an API? Give an example of an API mediating a system call.A programmer accesses an API via a library of code provided by the OS. Example: the system call CreateProcess() invokes the NTCreateProcess() in the Windows API
- 9Why is the API necessary to mediate system calls?1)Program portability: a program can compile and run on any system that supports the API
2)System calls can be difficult to work with
3)The API allows access to high level objects
(ex: Java API) - 10The _____ selects an available process for program execution on the CPU.The process scheduler selects an available process for program execution on the CPU.
- 11How does the CPU use time sharing to create the illusion of job concurrency?A program loaded into memory and executing becomes a process--processes execute for a short time (a few milliseconds) before finishing or being interrupted. While waiting for one process to finish, the CPU begins a new process until that process is interrupted, etc. The CPU scheduler controls this cycle, executing once every 100 milliseconds.
- 12What is swapping, and when does it occur?Processes are swapped between the main memory (for execution) and the backing store (when idle or completed) to keep a steady flow of jobs available to the CPU. Swapping occurs when the dispatcher exchanges a process desired by the CPU for one currently in memory.
- 13An address generated by the CPU is called a ______, while an address loaded into memory is called a ________. The user program deals mainly with the ____.An address generated by the CPU is called a logical address, while an address loaded into memory is called a physical address. The user program deals mainly with the logical address.
- 14The run-time translation from logical to physical addresses is by a hardware device called the _____.The run-time translation from logical to physical addresses is by a hardware device called the memory management unit (MMU).
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- Flashcards on OS, created by Brenna Cantwell on 18/07/2016.
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- Brenna Cantwell
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