Question 1s Flashcards
List three objectives of a good scheduling policy for an operating system
Fairness, Efficiency and low response time
Distinguish high level
High level scheduler (HLS) is responsible for a process that need servicing into a order. As a job enters the queue it is placed in the ready to process queue.
Compare and contrast (FCFS) and (SJF).
First come first serve - Jobs are execute first come, first serve basis. It is a non-preemptive scheduling algorithm. Easy to understand. Shortest Job First This is a non-preemptive scheduling algorithm. Best approach is to minimize wait time. The processor should know in advance how much time it will take
What is the relationship between the low level scheduler and the dispatcher?
A scheduler will evaluate requirements for requests to be serviced and thus imposes an ordering.A CPU dispatcher sets up user registers, memory mapping… everything a process needs to actually run
How does the wait time differ from each of the algorithms FCFS and SJF
FCFS - P0 0-0=0 P1 5-1=4 P2 8-2=6 P3 16-3=13 Average wait = 0+4+6+13/4= 5.75 SJF - P0 3-0=3 P1 0-0=0 P2 16-2=14 P3 8-3=5 Average wait = 3+0+14+5/4 =5.50
What is an operating System?
An operating system is software that manages computer hardware and software resources that provide common services for computer programs
What do operating systems do?
An operating system has 3 main functions, manage the computer resources, establish a user interface and execute and provide services for application software .
What resources need to be managed by modern operating systems?
such as disk drives, memory and processors/cores.
Describe with the aid of a diagram the microkernel approach to operating system design give advantages and disadvantages
The microkernel approach is to define a very simple abstraction over the hardware, with a set of primitives or system calls to implement minimal OS services such as thread management, address spaces and interprocess communication. All other services, those normally provided by the kernel such as networking, are implemented in user-space programs referred to as servers. Microkernels generally underperform traditional designs, sometimes dramatically. This is due in large part to the overhead of moving in and out of the kernel, a context switch, to move data between the various applications and servers
Advantages/disadvantages of Microkernel
The architecture of this kernel is small and isolated hence it can function better. Expansion of the system is easier, it is simply added in the system application without disturbing the kernel. Unfortunately, microkernels can suffer from performance decreases due to increased system function overhead
Who developed the Android operating system?
Andy Rubin, Rich Miner, Nick Sears developed the android operating system.
Describe the Android operating system
Android is a mobile operating system developed by Google. It is based on a modified version of the Linux kernel and other open source software and is designed primarily for touchscreen mobile devices such as smartphones and tablets. The only difference is that the Android version is a bit more advanced than that of the Linux. Main reason being the android kernel consists of additional features such as the wakelocks, double-tap to unlock and other similar features embedded into the mobile operating device. Features such as wakelock are important since the kernel is going to work on a portable device and it needs to be a bit more aggressive in memory and battery management; unlike the basic linux where energy management is not an issue
Distingusish Medium level scheduling
Medium level scheduler (MLS) Is a process is in a running state and it needs one peripheral device usage, it is taken out of the Running state and put into the blocked queue. It is the job of the medium level scheduler to move a process in and out of IAS as necessary
Distingush low level scheduling
Low level scheduler(LLS) Once the process are in the IAS, the low level takes control it will select the next most appropriate process to give the CPU
