Operating System Architecture
Q?What is operating system?
/>User → ||OperatingSystem||→ ComputerHardware
/> OS executes the user programs and solves user problems
/> OS makes the computer systems(Computer hardware, application
programs) easy and convenient to use
/> defined as a Resource Allocator – manages and allocates
resources: who, when, how much time, how many
/>defined as a Control Program – controls the execution of user
programs and operations of I/O devices
/>defined as Kernel – the one program running at all times
Q?Simple Batch Systems
/>this are the very first version of operating system.
/> It works on the principle of Automatic job sequencing : i.e. we
automatically transfer control from one job to another.
/> It consist of Resident Monitor : the initial control is in
monitor; then the control transfers to the job ; when the job
completes the control transfers back to the monitor.
Q?what is the memory layout for a Simple Batch Systems
/> The memory layout consist of two half: one half for Resident
Monitor and another half for user.
/> in the monitor area we have :interrupt and tap vectors- Device
driver– job sequencing- control card interpreter
/>the size of the area is seperated by the Fence Register
Q?In Simple Batch Systems how does the monitor know about
the nature of the job or which program to execute ?
/> to distinguish a job from job or data from program we introduce
the control cards
Q?What are this Control Cards
/>These are the special cards that tell the resident monitor which
program to run.
/> we can distinguish this control cards from data/program cards
$ JOB
$ RUN
//Data
Q?what are the parts of Resident Monitor
/> It consist of :
1> Control card interpreter :responsible for reading and carrying
out instructions on the cards.
2> Loader : loads system programs and application programs into
memory
3> Device Driver : Helps to run each of the system's I/O devices
knowing all its special character and properties
Q?How will you solve the problem of slow performance in Simple
Batch Systems
/> The overall throughput(amount ofjobs/total time taken) is very
low of about 33 job/hour,and this is caused by slow card reader
and because the I/O and CPU do not overlap with each other.
We can solve this problem by doing Off-Line operation: this consist
of loading jobs into memory from tapes.
The card reading and line printing is all done Off-Line. By doing this
we could increase our throughput to 55job/hour.
Q?Multiprogramming Batched Systems
/> we take several jobs and keep it in main memory at the same time,
and the CPU is multiplexed among them.
/> we use a special technique called Spooling in multiprogramming:
in Reading part we read the next job from card reader into a storage
area on the disk(inside job queue)then in Writing part we output
printout of previous job from disk
/> Job Pool – is the data structure that allows the OS to select
which job to run next to increase CUP utilization
Q?what kind of OS features are needed for Multiprogramming
/>System must have the I/O routine
/>Memory management must be done for several jobs
/> CPU scheduling should be done to choose among several jobs ready
to run
/> we have to allocate the devices
Q?Time-Sharing Systems
/>Various Jobs are kept in the memory and on the disk to execute.
For that we perform Time-Sharing by multiplexing CPU to several jobs.
Only if there are jobs in the memory then the CPU is allocated.
/> So various swapping of the job in and out of memory is occurred
/> Online communication between the user and the system is provided,
when the OS finishes execution of the command.
Q?Personal-Computer Systems
/>this are the systems made for single user
N.B. *we are discussing the migration of OS concepts and features
till now .
Q?Parallel Systems
/>These are the Multiprocessor systems with more than one CPU in
close communication.
/> all this processors they share the memory and a clock so the
communication takes place in same memory
YouTube:
https://www.youtube.com/watch?v=qKJxdIHjOwg&feature=youtu.be
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