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operating systems
midterm 1
35
Computer Science
Undergraduate 3
09/28/2010

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Term
Job pool
Definition
contains all processes residing on the disk that await allocation of main memory.
Term
mode bit
Definition
indicates whether a task is being executed on the behalf of the user(1) or the kernel(0). when executing a user application it is 1. when executing a the kernel is performing an operation it is 0.
Term
process
Definition
a program that is executing. an active entity that needs resources such as CPU, memory, and files. Progresses sequentially.
Term
batch computing
Definition
give a computer a batch of jobs to complete with out interaction from the user.
Term
all i/o instructions are (privileged or non privileged)
Definition
privileged
Term
interrupts cause a switch to which mode?
Definition
kernel mode
Term
timer
Definition
program used to limit the amount of time a process can run uninterrupted.
Term
trap aka exception
Definition
software generated interrupt
Term
multi tasking OS
Definition
cpu is multiplexed between various programs that are running concurrently. there is an interaction between user & the machine
Term
kernel
Definition
the part of the OS that stays in memory
Term
new(process state)
Definition
when the process has been created
Term
ready(process state)
Definition
all resources have been allocated except for the cpu. the process is currently waiting for cpu allocation
Term
run(process state)
Definition
the cpu is allocated to a process
Term
wait(process state)
Definition
process is waiting for an event to occur
Term
terminated(process state)
Definition
process has completed
Term
process control block(pcb)
Definition
represents a process. contains information on process state ,program counter. cpu registers, scheduling info(cpu & memory). accounting info.
Term
job table
Definition
a table containing all of the jobs in the system.
Term
longterm scheduler
Definition
chooses one of the new jobs(from the job pool) to bring to the ready state, used every few milliseconds.
Term
short term scheduler
Definition
chooses one of the ready processes (stored in main memory) to execute when the cpu becomes available.
Term
medium term scheduler
Definition
used when a job is "executing" but not making any progress. this scheduler removes these jobs from memory. also called when a processor needs to be switched out for another for CPU efficiency.
Term
layered OS
Definition
top layer is UI. bottom layer is hardware. each layer is build off the function cals available from the previous layer. API on a very large scale. causes large amounts of overhead.
Term
structure of original unix kernel
Definition
kernel acts as a middle man between hardware and application programs. kernel is very large and contains file system, memory management ,etc.
Term
problems with original unix kernel
Definition
too bloated. makes maintenance and debugging very difficult.
Term
problems with layered os
Definition
massive amounts of overhead is generated from all of the function calling
Term
benefits of layered os
Definition
bugs are easily isolated to individual layers. once the lower layers have been debugged, the upper layers can easily be debugged.
Term
mach os(microkernel)
Definition
all non essential components of the kernel have been removed. these components are reimplemented as system & program applications. the items left in the kernel are minimal resource management and message passing.
Term
benefits of microkernel
Definition
easy to add functionality to, easy to debug. safe, since most items are being run as application processes
Term
thread
Definition
basic unit of cpu work. part of a process.
Term
context switch
Definition
the system saves the state of the current process ( current instruction, the program counter, etc) and picked up latter after the cause of the context switch has been dealt with.
Term
msgget(msgque ,flag)
Definition
used to get the message queue id of a message queue or make a message queue. returns the id.
Term
symmetric adressing
Definition
occurs in message passing. the sender and receiver must know each other's names.
Term
asymmetric addressing
Definition
receiving process does not care who sent the message.
Term
synchronous message passing(blocking)
Definition
the sender & receiver wait until the msg has been sent/received.
Term
types of buffering
Definition
unlimited- not actually infinite, just really large. producer never has to wait. consumer has to wait for a message to be created.

bounded - fixed size. producer may have to wait for buffer to be emptied(aka their previous messages have been read). consumer has to wait for a message to be created.

none- zero size. sender has to wait for receiver to request data. receiver will wait fro sender to send data.
Term
pipe
Definition
uni-directional. can't be accessed outside of fathering process. generally used to communicate with children. once communication ends, the pipe dies.
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