MEMORY MANAGEMENT OF OPERATING SYSTEM
DEFINITION
- a pool of memory
- allocating space
FUNCTIONS
- preserve the memory ~ coordinate
- main memory
- keep track
ex: RAM, ROM
PROCESS MANAGER ( ALGORITHM )
FIRST COME FIRST SERVE
- non-premptive
- handle jobs according to their arrival times
- turn around time is unpredictable with the FCFS policy
SHORTEST JOB FIRST
- non-premptive
- handle jobs based on the length of the CPU cycle time
PRIORITY SCHEDULING
- non-premptive
- most common
SHORTEST REMAINING TIME
- premptive version
- if a new process arrives with CPU burst length less than remaining time of current executing process
- ready queve
Memory Management Strategies
Placement
Replacement
Fetch
Best fit
Worst fit
First fit
Swapping Technique
Swap – out operation - by copying its instruction and data onto a disk
Swap – in operation - by loads another process in this area of memory
Major System Resource Types within a Computer System
Throughput
Electrical power
Network
Hard Disk space
Memory
CPU Time
External devices
States of a Process
Blocked : For an event to occur
Run : Instruction execution
Ready : Assign a process to a processor
Terminated : Finish execution
New : Created
Purpose of CPU Scheduler
Medium Term Scheduler
Long term scheduler / Job Scheduler
Short term scheduler/ CPU scheduler/ Dispatcher
Scheduling Creteria
Turnaround time
Waiting time
Throughput
Response time
CPU utilization
Deadlock
Four condition for deadlock to Occur
Hold and Wait - condition means a situation where in a process owns a resource and claiming the other resource
No preemption - condition means a situation where the granted resource to a process cannot be taken back by the operating system forcibly.
Mutual Exclusion - means that a resource is assigned to only one process at a time.
Circular wait - is a situation where each waiting process is waiting for the next process in the chain and none is able to get the resource.
Method for handling deadlock
Detect and Recover from Deadlock
Ignore the deadlock
Prevention and avoidance of deadlock
Avoid the deadlock