Full transcript
0:00hello friends welcome to today's
0:02operating system class and in this class
0:04we will see
0:05the operating system structure
0:09and this will come under first unit
0:10operating system overview and system
0:12structure
0:13right so in this class we will see
0:15the simple structure
0:17layered approach micro kernels and
0:19models so these four structures we are
0:22going to discuss in this class
0:26if the operating system is very large
0:28and complex then it should be engineered
0:30carefully to function properly and also
0:34it should be modified easily then only
0:36it will become a very good operating
0:38system
0:39if the task is very large then we need
0:41to partition that into small components
0:44or modules
0:46then each of these modules should be
0:48well defined portion
0:50of your system
0:52okay that is carefully defined input
0:55output and functions
0:58and there are four different structure
1:00of this operating system based on how
1:03the components are interconnected to the
1:06kernel because kernel is the heart of
1:08operating system
1:09here we are going to discuss the simple
1:12structure layered architecture
1:14microkernel architecture and modular
1:17architecture let us see all these things
1:19one by one
1:21first let us see the simple structure
1:23and the ms-dos is the
1:25very first operating system and it is
1:28having very limited functionalities
1:32right so here this is the first layer
1:34that is hardware layer here we are
1:37having room that is read-only memory
1:40bias basic input and output systems and
1:43other device drivers are there and this
1:45is the second layer this is os layer
1:48which way is okay and this is the third
1:52layer we are having system programs and
1:54this is the last layer application
1:56program okay hence this structure is
1:59very small simple uh so it is having
2:02very limited functionalities
2:04okay and
2:06in this structure the interfaces and
2:09levels of functionalities are not well
2:12separated
2:13that means
2:15the system programs and application
2:17programs can also directly access the
2:19hardware
2:21okay system programs and
2:23application programs can also directly
2:25access rvc application programs are able
2:27to access the basic io routines to write
2:31directly to display
2:33and the disk devices
2:40if all the layers can access the
2:42hardware directly hence the ms dash will
2:46be vulnerable to malicious program that
2:48means all the virus or any other malware
2:51program can easily affect or attack this
2:54ms das which causes the entire program
2:57crashes when the user program fails
3:00and it is having a limited hardware also
3:04because
3:07the ms does is written for the processor
3:108088
3:12okay by using the assembly language
3:15and it provides no dual mode and no
3:18hardware protection
3:25the second one is layered approach
3:27here the operating system is broken into
3:29number of layers layer is otherwise
3:32called as levels so in this diagram we
3:34are having
3:35a hardware
3:37layer
3:39this is layer 0
3:40and finally we are having user interface
3:43layer in between we are having some
3:45other layers also os layer may be here
3:48okay the bottom layer is hardware layer
3:50and the topmost layer is user interface
3:52layer okay and the main advantage of
3:56layered approach is
3:59the simplicity of the structure
4:01and debugging and system verification is
4:04very easy
4:06okay and the design and the
4:08implementation of the system are very
4:10much simplified when compared to the
4:12previous the simple structure each layer
4:16hides the existence of certain data
4:19structures operations and hardware from
4:22higher level layers
4:24okay
4:25here
4:26the layer 1 will access layer 0
4:29and the layer 2 will access layer 1 and
4:32layer n will access layer n minus 1 so
4:35the axis will goes in this way hence
4:38each layer will hides the data structure
4:42operations and hardware from higher
4:45level layers
4:47the main difficulty of this layered
4:50approach is
4:51defining the various layer how we are
4:54going to define each and every layer
4:57that is we need to separate the
4:58functionalities to the layers because
5:02the higher level layer will use only the
5:05lower level layers hence the careful
5:08planning is very much if necessary here
5:11in this layered approach
5:14the third structure is microkernel
5:16structure
5:17means
5:18the non-essential components will be
5:21removed from the kernel
5:23and those will be moved to either system
5:26programs or user level programs hence
5:28the size of kernel will be very much
5:30reduced to that is to micro kernel here
5:34we will face very little difficulty that
5:36is which service should be in the kernel
5:39and which service should move to the
5:42user space
5:43okay that means we are going to remove
5:46the unessential component from the
5:48kernel hence we should have some
5:50knowledge about which component will be
5:53the unnecessary and that will be moved
5:55to user space
5:58the micro kernel will provide
6:01minimal process
6:03memory management and communication
6:05facility
6:09and this is the example for micro kernel
6:12here
6:13the layer one which is hardware all the
6:16hardware will be there and this is os
6:18layer second layer from this os layer
6:23the inter process communication memory
6:25management and cpu scheduling will
6:27remains in the kernel mode itself and we
6:31can move this file system and device
6:33driver to the user mode
6:37okay hence the size of kernel will get
6:39reduced
6:42the micro kernel provides communication
6:45between the client program
6:46because maximum services will run only
6:49in the user space
6:51and the communication will be taken
6:52place through message passing
6:55and let us see the advantages
6:57extending the operating system is very
6:59easy without affecting the kernel or
7:02without modifying the kernel we can
7:04easily extend the functionalities
7:06maximum functionalities will be run in
7:08the user space only and portability is
7:11another advantage we can easily move the
7:14operating system from one hardware to
7:16another hardware
7:18and
7:19it is more security and reliability
7:22since maximum services will run in the
7:26user not the kernel mode okay if any of
7:30the service fails then the rest of the
7:32operating system remains untouched
7:36okay that will not affect the kernel
7:40the only drawback of microkernel is
7:44it will suffer due to increased system
7:46function overhead
7:49because we cannot decide
7:51the function
7:53that should be either
7:55run in the user mode or in the kernel
7:58mode
7:59okay we need to design that carefully
8:02otherwise the micro kernel structure
8:04will get failed
8:08the fourth one is modular structure
8:11current operating system will follow
8:13only these modules
8:15that is loadable kernel modules
8:19here the kernel has the core components
8:22that is core modules and it is having
8:25links in additional services via those
8:28modules either by the boot time or the
8:31runtime
8:32so on demand the services will be loaded
8:35into the kernel and the kernel provides
8:37core services all the core services will
8:40be loaded only in the kernel and other
8:42services are implemented dynamically so
8:46based on the requirement the services
8:47will be implemented
8:50while the kernel is running
8:52here the cpu scheduling and memory
8:54management algorithms are directly
8:57loaded into kernel
8:58and the additional support of that is
9:02the different file system may be
9:05located in the loadable modules
9:08so on demand basis the modules will be
9:11loaded into kernel during runtime
9:15let us see the solarize loadable modules
9:18here
9:19the operating system is organized
9:22around the
9:24core solarize kernel that is core kernel
9:27with seven types of
9:30kernel modules okay
9:32scheduling classes
9:34file systems loadable system calls
9:38and executable formats
9:40and fifth one is streams modules and
9:43sixth one is miscellaneous modules and
9:46seventh one is device drivers buses and
9:49other drivers okay everything will be
9:53located as a modules
9:56up to this we have seen the operating
9:58system structure and under this title we
10:00have seen
10:02the simple structure layered approach
10:04micro kernel and modules
10:08and
10:09this is the question time give the
10:11example for
10:12layered architecture and micro kernel
10:16architecture of operating system
10:17students please give your answer in the
10:19comment box
10:21thank you