L9 - Operating System Flashcards
What are three categories of external IO devices?
Human readable
Machine readable
Communication
What are the major functions of an IO module
Control and timing
Processor communication
Device communication
Data buffering
Error detection
What are the three techniques for IO operations?
Programmed IO - Sequence of commands; program must wait for IO operation to finish - wasteful of processor time
Interrupt-Driven IO - Most IO devices; processor issues IO command then interrupt is generated when IO operation is completed; processor then handles the interrupt and IO data
Direct memory access - IO module and main memory exchange data directly without processor involvement
What are the four IO commands?
Control - used to activate a peripheral and tell it what to do
Test - used to test various status conditions
Read - read data from peripheral and place in internal buffer
Write - take item of data from data bus and transmit to the peripheral
What is the most important system program?
Kernel - contains OS core and is always resident in main memory
What are the typical services provided by an OS?
Program creation
Program execution
Access to IO devices
Controlled access to files
System access
Error detection & response
Accounting of resources
what are 4 desirable features of an os?
Priviledged instructions - can only be executed by the operating system, error interrupt if encountered in a program. IO operations priviledged
Timer - prevent a job from monopolizing the system. If timer expires an interrupt occurs and system regains control
Memory protection - User program only allowed to access some areas of memory, error if program tries to access restricted areas
Interrupts - give system more flexibility
What are the 3 types of operating systems?
Interactive system - user interacts with computer to request job
Batch system - Users program batched together with other programs
Uni/multi programming - Uni - can only run one program at a time
Multi - semi simultaneous; can run multiple programs at a time
What is a time sharing OS?
User interacts
Processor time shared between multiple users
Multiple users simultaneously access system
Not to be confused with multiprogramming
Users see 1/n of effective computer speed
What is long term scheduling?
Decision to add to pool of processes o be execuyted
What is medium term shceduling?
Decision to add to number of processes partially or fully in memory
What is short term scheduling (dispatching)?
Decision as to which process will be executed by the processor
What is IO scheduling?
Desicion as to which process’s pending IO request shall be handled next
What is fixed partitioning?
All memory partitions have same size - caused small programs to take massive amounts of space if partitions were too big
large processes need multiple partitions
What is dynamic partitioning?
Each partition has a different size but fixed location; fragmentation
difficult to track full process location
