Scheduling Flashcards
Where are multiple jobs managed?
memory
what kind of alternation takes place with jobs?
those waiting to use the CPU and those waiting for IO.
the key to multiprogramming is [x]
scheduling
what does the high level scheduler do?
determines which programs are admitted to the system for scheduling
the high level scheduler controls the [x x x]
degree of multiprogamming
In a batch system, where do newly scheduled jobs go and how are they held?
routed to disk and held in a queue or waiting line
when adding a job, the high level scheduler must take two decisions. what are they?
1) scheduler needs to know it can take on one or more processes
2) it needs to decide which jobs to turn into processes
how often does the high-level scheduler execute?
relatively infrequently.
what coarse decision does the scheduler usually make?
whether or not to take on a new process
what is the short term scheduler also known as
dispatcher
how often does the short term scheduler run
frequently
from a high level, what does the short term scheduler decide
which job to execute next
the status of a process at any point in time is its [x]
state
what are the five states of a process?
new ready running waiting halted
define new for a process state
the program has been admitted but is not ready to execute. It needs to be moved from the operating system to a ready state.
define ready for a process state
process is ready to execute and is awaiting access to the processor
define running for a process state
the process is being executed by the processor
define waiting for a process state
the process is suspended from execution waiting for some resource, like I/O
define halted for a process state
the process has terminated and will be destroyed by the operating system. Oooo errrr
what must the operating system hold about each process?
its state
where does the operating system hold the process state information?
process control block
what eight things are held in the process control block?
identifier state priority program counter memory pointers context data I/O status information Accounting information
define identifier for the process control block
a unique id associated with a process
define state for the process control block
the state of the process
define priority for process control block
relative priority to other processes
define program counter for process control block
the address of the next instruction in the program to be executed.
define memory pointer for process control block
the starting and ending location of the process in memory
define context data for process control block
data present in the registers while the process is executed
define I/O status information
includes outstanding I/O requests, I/O devices (eg., tape drives) assigned to this process, a list of files assigned to the process, and so on.
define accounting information
information on processor time and clock time being used
when the processor accepts a new job or a request, what does it do?
creates a blank process control block
when the process block is fully filled in, what happens to the process state?
it is moved to ready
What happens in an I/O operation?
Processor saves current context data and the program for A in A’s process control block.
The operating system may perform some work like initiating I/O stuff.
Short term scheduler decides which process should be executed next.
The operating system instructs processor to restore B’s context data and proceed with B.
What is the long-term queue
a lost of jobs waiting to use the system
