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Operating System Mid Term EECS 325
Operating Systems (Concurrency, Threads, Processes)
26
Computer Science
Undergraduate 4
03/03/2016

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Term
Kernel
Definition
The one program running at all times, this is basically the operating system at its core.
Term
System Call
Definition
Calls to functions in kernel space.

The programatic way in which a computer program requests a service from the kernel of the operating system it is executed on.
Examples: Exit, Wait, Fork, Write
Term
System Libraries
Definition
User-level libraries whose functions have possibly multiple system calls.
Term
Process Scheduler
Definition
Selects among available processes for next execution on CPU. Maintains scheduling queues of processes.
Processes migrate among the various queues.
Term
Job Queue
Definition
Set of all processes in the system
Term
Ready Queue
Definition
Set all processes residing in main memory, ready and waiting to exectute
Term
Device Queues
Definition
Set of processes waiting for an I/O device
Term
Process Scheduling Diagram
Definition
[image]
Term
Long-term Schedulers
Definition
Select which process should be brought into the ready queue.

AKA Job Scheduler

Invoked very infrequently (seconds, minutes) => May be slow

Controls the degree of multiprogramming because in the ready queue as many programs that are there is your level of multiprogramming
Term
Short-term Schedulers
Definition
Selects which process should be executed next and where in the ready queue the processes leaving the CPU goes

AKA CPU Scheduler

Invoked very frequently (ms) => Must be fast
Term
Program
Definition
A piece of code; a passive entity (does not have a program counter, does not have variables initialized, etc.)
Term
Process
Definition
A program in action. Has:
Program Counter
Register/variables in use
Opened files,
etc.
Term
fork()
Definition
The "parent" process executing the fork creates another "child" process whose address space is identical but separate from the parents own address space.
Term
vfork()
Definition
The "parent" process executing the vfork() creates a "child" process who shares exactly the same address space as its parent who created it.
That is,if one changes an instruction, variable, environment var, etc., the other see the changes immediately.
Term
Two I/O Methods Diagram
Definition
[image]
Term
Synchronous vs Asyncrhonous I/O
Definition
Requires the process to wait while I/O is completed. Asynchronous I/O allows the process to tend to other tasks while I/O completes.
Term
Spooling
Definition
Spooling is a concept from batch-oriented operating systems; it involves, for the sake of increased turnaround time, overlapping of the output of one job with the input of other jobs.
Term
Semaphore vs Critical Regions and Monitors
Definition
Semaphores are powerful synchronization tools, but are easy to misuse. Therefore critical regions and monitors are also proposed as synchronization tools.
Term
Concurrent Programming
Definition
In concurrent programming several streams of operations may execute concurrently. Each stream of operations executes as it would in a sequential program except streams can communicate and interfere with one another. Each such sequence of instructions is called a thread.
Term
DMA-based I/O
Definition
Refers to the environment where device controller transfers blocks of data from buffer directly to memory without intervention from the CPU and vice versa. This results in one interrupt generated per block instead of one interrupt per byte.
Term
Caching
Definition
Refers to process where data being used is copied from slower storage to faster storage temporarily in order to reduce data access times.
Term
Modularization Tools
Definition
Processes, procedures, and abstract data types.
Term
Critical Section
Definition
Segment of code in which a process may be changing common variables, updating a table, writing a file, and so on.
No two processes are executing in their critical section at the same time.
Each process must request permission to enter its critical section.
Term
Mutual Exclusion
Definition
If process Pi is executing in its critical section, then no other process can be executing in its critical section.
Term
Bounded waiting
Definition
There exists a bound, or limit, on the number of times other processes are allowed to enter their critical section after a process has made request to enter its critical section and before that request is granted.
Term
Progress Property
Definition
If no process is executing in its critical section and some process wishes wish to enter their critical sections, then only those processes that are not executing in their remainder section can participate in deciding which will enter its critical section next, and this selection can not be postponed indefinitely.
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