Operating
Systems Theory & Design
Modern operating
systems have common major functions and services. While their specific implementation may vary between the operating system and computing environment, they all have User and System services
that provide the main functions of any OS.
These include Program Execution, I/O Operations, Resource Allocation, File
Systems, Protection & Security, and Error Detection, among others.
Figure 1- Major Functions and Services of Operating Systems
Processes Control & Management
Operating systems
enable processes to share, exchange and manage information and resources. This function is implemented via a Process Control
Block, which is a data structure that contains all process-related information,
including the current state of the operating system. From the process ID, registers, memory, and
files used, the Process Control Block (PCB) is the quarterback of every process.
Figure 2- Process, Threads and Process Synchronization
Operating systems
enable processes to share, exchange and manage information and resources. This function is implemented via a Process Control
Block, which is a data structure that contains all process-related information,
including the current state of the operating system. From the process ID, registers, memory, and
files used, the Process Control Block (PCB) is the quarterback of every process.
Modern processors
and computing needs have demanded a solution that allowed multiple processes to
be executed in parallel as opposed to sequentially. To accomplish this, multi-core and
multi-threaded processors were developed to allow for processes with multiple
threads to be executed. A thread is
considered to be a light process, but can only exist inside a process. The benefit is that every thread has its own
registers, counter, stack, but shares data, files, and code with the other
processes being executed in parallel. This
has vastly improved process execution.
Critical Section Problem
The
critical-section is a code segment that accesses shared variables and has to be
executed as an atomic action. 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.
For example, if
two processes are running, and both need to access the same file, the software
needs to be written in a way that these two processes are not executing their
critical-sections at the same time. Otherwise, one process may be editing a
file that the other process is trying to access at the same time. This can
cause the program to throw an exception error.
The
critical-section problem can be solved by implementing mutual exclusion in the
code, progress, and bounded waiting. The
code below is an example using the Peterson Solution:
do {
flag[i] = true;
turn = j;
while(flag[j] && turn == j);
critical section
flag[i] = false;
remainder section
}
while(true);
In this solution,
when a process is executing in a critical state, then the other process only
executes the rest of the code, and the opposite can happen. This method also
helps to make sure that only a single process runs in the critical section at a
specific time.
Memory Management
Memory management
is a main function of the Operating System.
Its primary responsibility is to manage memory and move processes and
related process data back and forth between the physical memory and the virtual
memory on the disk. It decides which
process will get what memory at what time, based on the knowledge of what
memory is free and available.
Memory in a
computer is dynamically allocated depending on the needs of the application and
processes being executed, and it is freed up when the process no longer
requires the memory, thus allocating that slot of memory to another process if
needed.
Ultimately how
memory is managed will depend on how effective the hardware, operating system,
and programs or applications are programmed and/or configured.
Figure 3- Memory Management
File Systems Management
File management
is a key function of the operating system.
It is also one that most of us interact with frequently, even if we
don't specifically interact with the OS in a terminal. All applications that open and save files are
calling on the OS to locate, open, edit, save or delete files.
A file is a
collection of information saved on secondary storage and loaded into
memory. File management can be thought
of as the process of manipulating files on a computer. There are several logical structures of a
directory as shown in Figure 4 below:
Figure 4- File Systems Management
/ Directory Structures
|
Each of these
directory structures provides advantages and disadvantages. For example, the single directory structure
is easy to implement, and manipulating files in this structure is easier and
faster. A disadvantage in this structure
is that name collisions can occur and searching can become time-consuming if a
directory structure is long.
The two-level
directory is a bit more robust in that you can have different users, and each
can contain directories and files of the same name. Searching in this structure also becomes
easier; however, a user cannot share files with other users.
Tree-structured
directories are the most common. This is
what we experience in the Windows OS environment. It is scalable, easy to search, and can use
both absolute and relative paths.
Despite its popularity, this structure cannot share files and is
considered inefficient.
The acyclic graph
is a graph with no cycle and allows users to share subdirectories and files.
The same file or subdirectories may be in two different directories. I think of
it as a souped-up tree-structured directory.
In general graph
directory structure, cycles are allowed within a directory structure where
multiple directories can be derived from more than one parent directory. The
main problem with this directory structure is to calculate the total size or
space that has been taken by the files and directories.
OS Security & Protection
The goal of
security is to protect the computer system from various threats, including
malicious software such as worms, trojans, viruses, and unwanted remote
intrusions. Security typically involves
the implementation of control techniques that can protect a computer from
unauthorized changes to files, configurations, and even access to specific
applications and resources attached to it.
The most common
methods employed in protecting computer systems include the use of antivirus
and antimalware software, as well as other administrative system policies
requiring regular OS system updates, user access control, and even physical
access control.
Figure 5- Security and Protection
Conclusion
Having a more in-depth understanding of all of these important concepts about operating systems
will play a key role in my future as an IT professional. From deployment of
security systems to programming for specific environments, my understanding of
resource management will be helpful in delivering a more optimized product for
my internal stakeholder.
