CPT 304: Operating Systems Theory Concept Map Summary Blog Post
CPT 304: Operating Systems Theory Concept Map Summary Blog Post
During the
time we spent in CPT 304 we reviewed a substantial amount of information
spanning many aspects of Operating systems and their design. In order
to start to understand operating systems we must first understand what
operating systems do and what their purpose is. The three main purposes
of an operating system are that it provides an environment for a
computer user to execute programs on computer hardware in a convenient
and efficient manner; it allocates the separate resources of the
computer as needed to solve the problem given. The allocation should be
as fair and efficient as possible; control Program that serves the
function of supervision of the execution of user programs to prevent
errors and improper use of the computer as well as manage the operation
and control of I/O devices.
Examples of Operating System Components are:
- Accounting
- Error Detection
- Protection Security
- I/O Operations
- Communications
- Program Execution
- Resource Allocation
- File Systems
- User Interface.
As a process executes, it changes state, The state is referred to the Process State and could be one of the following:
- New: The process is being created
- Running: Instructions are being executed
- Waiting: the process is waiting for some event
- Ready: The process is waiting to be assigned to a processor
- Terminated: The process has finished
Control Block is a data structure in the operating system kernel
containing the information needed to manage a particular process. The
PCB is "the manifestation of a process in an operating system".
The role of the PCBs is central in process management: they are
accessed and/or modified by most OS utilities, including those involved
with scheduling, memory and I/O resource access and performance
monitoring. It can be said that the set of the PCBs defines the current
state of the operating system. Data structuring for processes is often
done in terms of PCBs.
The critical
section problem refers to the problem of how to ensure that at most one
process is executing its critical section at a given time. One way to
solve for that is Peterson's solution. Peterson's solution is restricted
to two processes that alternate execution between their critical
sections such as demonstrated below.
When
processes run they require memory to complete operation and terminate. A
way that a process uses memory is it searches for available memory
partitions called “holes”. An operating system can order the process
queue according to a scheduling algorithm where memory is allocated to
processes until, the memory requirements of the next process cannot be
satisfied. If no available partition of memory is large enough for the
process; the operating system can then wait until a large enough
partition is available, or it can skip to the next process queue to see
whether the smaller memory requirements of some other process can be met
(Silberschatz, 2014). Memory blocks available comprise of a set of
“holes” (memory partitions) of various sizes scattered throughout
memory. When a process arrives and needs memory, the system searches the
set for a hole that is large enough for this process if the hole is too
large, it is split into two parts. One part is allocated to the
arriving process; the other is returned to the set of holes. When a
process terminates, it releases it’s a block of memory, which is then
placed in the set of holes. If the new hole is adjacent to other holes,
these adjacent holes are merged to form one larger hole. The system may
need to check whether there are processes waiting for memory and whether
this newly freed and recombined memory could satisfy the demands of any
of the waiting process. This procedure is called the dynamic allocation
problem, which is the process of how to satisfy a request of size n
from a list of free holes.
A file system is the most
visible aspect of an operating system. It provides the mechanism for
online storage and access to both data and programs of the operating
system and all users of the computer system (Silberschatz, Galvin &
Gagne, 2014). A file system consists of two parts, the collection of
files and the directory structure. The directory structure is what
organizes and provides information about the files in the system.
Operations such as searching for a file, creating a file, deleting a
file, listing a directory, renaming a file, and traversing the file
system are a few things you can perform. There are different types of
directories used to store files.
Single-level
directories are considered the simplest directory structure where all
files are stored within the same directory; however, while it provides
an easy to understand and support directory, this type of directory has
limitations. If two or more users all use the same directory the
directory will fill up with files quickly and users will also have to
make sure to use their own unique file names as they cannot have
multiple files that are named the same.
A
two-level directory structure has its own user file directory (UFD) for
each user. If there are other users, they will not be able to read,
write, or delete a different user's files and when searching for files
it will only search files within the user's own UFD. The disadvantages
of a two-level directory however is that it makes user files completely
independent which can have detrimental effects if users need to
cooperate on a project or share a file as a two-level directory will not
allow a user to access the files of another user.
One of the other main jobs of
an operating system is I/O or input/output; the OS’s role is to manage
and control I/O operations and I/O devices (Silberschatz, Galvin &
Gagne, 2014). Examples of I/O devices are devices such as a mouse,
keyboard, hard disk, monitor; many would have to use a type of device
controller or driver that will allow the hardware to communicate to the
computer with a software intermediary.
In
the principles of protection; protection refers to a mechanism for
controlling the access of programs, processes, or users to the resources
defined by a computer system. This mechanism must provide a means for specifying the controls to be imposed, together with a means of enforcement. One such mechanism would be an access matrix. An access matrix is an abstract model of protection where the rows represent domains, and the columns represent objects. Each entry in the matrix consists of a set of access rights.
Protection
is an internal problem; however security is considered both the
computer system and the environment (people, buildings, businesses
valuable objects, and threats) within which the system is used. Most
methods of preventing or detecting security incidents include intrusion
detection systems, antivirus software, auditing and logging of system
events, monitoring of systems software changes, system-call monitoring,
and firewalls.
In
Language-based protection; as systems have developed, protection
systems have become more powerful, and also more specific and
specialized. To refine protection further requires putting protection
capabilities in the hands of individual programmers so that they can
implement protection policies at the application level. This would allow
them to protect resources that are known to the specific application
but not to the more general operating system. The general goal is to
provide three functions: Distribute capabilities safely and efficiently;
specify the type of operations a process may execute on a resource and
specify the order in which operations are performed on the resource.
In
Domain protection; a protection domain specifies the resources that a
process may access; each domain defines a set of objects and the types
of operations that may be invoked by each object. An access right is the
ability to execute an operation on an object, a domain is defined as a
set of object, pairs; some may be disjointed while others overlap.
Silberschatz, A., Galvin, P.
B., & Gagne, G. (2014). Operating system concepts essentials (2nd
ed.). Retrieved from https://redshelf.com/
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