Operating System is the software in the first layer that is placed in memory

computer when the computer is turned on. While other software is run

after the Operating System runs, and the Operating System will perform common core services for

those softwares. These common core services such as access to disk, memory management,

scheduling tasks, and user interfaces. So that each software is no longer needed

performs these common core tasks, because they can be served and performed by the System

Operation. The piece of code that performs core and general tasks is called the “kernel”

an Operating System.

Operating System is the link between the hardware layer and the software layer. More than that,

The Operating System performs all important tasks in the computer, and guarantees application-

Different applications can run simultaneously smoothly. Operating System guarantee

Other software applications can use memory, input and output

other equipment and have access to the file system. If several applications run accordingly

together, the Operating System sets the correct schadule, so as much as possible all

running processes get enough time to use the processor (CPU) as well

not interfere with each other. In a modern operating system, a large and complex system

has a structure that must be designed carefully and thoroughly in order to function

as desired and can be modified easily. Operating system structure

are operating system components that are connected and formed inside

the kernel.

The operating system structure in general are:

1. Simple Operating System Structure

This operating system structure that provides functional space in so little space

not divided into modules, initials are limited to functional hardware

which is divided into two parts, the kernel and the system program. The kernel is divided into a series

interfaces and device drivers and provide file systems, CPU scheduling, memory management,

and other operating system functions through the system call.


• Service can be done quickly because it is in one room.


• Testing and eliminating errors is difficult because it cannot be separated and


• Difficult to provide security facilities.

• Waste of memory when each computer must run the kernel, because of all the services

stored in a singular while not all services are needed.

• Errors in some functions cause the system to malfunction. Example of an operating system

which have simple structures are MSDOS and UNIX.

2. Structure of a Monolithic Operating System

Monolithic operating system structure is a simple structure that is equipped with dual

mode. This type of operating system can be defined as a collection of procedures where procedures

can be invoked by other procedures in the system when needed. The kernel contains all services

provided by the operating system for users. The operating system is written as a group

procedure, which can be called at any time by the user when needed.


• Services can be done very quickly because they are in one address space.


• Testing and eliminating errors is difficult because it cannot be separated and


• Difficult to provide security facilities.

• It is a waste if every computer has to run a very monolithic kernel

big while actually does not require all the services provided by the kernel.

• Not flexible.

• Programming errors in one part of the kernel cause the whole system to shut down.

Examples of operating systems that have a monolithic structure are the Linux Kernel and


Services in the Operating System

1. Making the program

The operating system simplifies and helps in accessing the debugger and editor process

that is already in the program in the form of a utility.

2. Execute the program

The operating system handles all tasks for the benefit of the user. Tasks include

Data instructions must be loaded into memory, I / O devices must be initialized included

also the file must be initialized, and other resources must be reserved.

3. Accessing I / O devices

The device in the I / O has its own instructions or signal control for operation. Service

given by the operating system is to maintain the details so that programmers can

think of it as a simple reading and writing operation.

4. Controlled access to files

Controlled testing is the file format contained in the storage media. more

The operating system further provides a protection mechanism to control access to files.

5. Detection and response to errors

An error or an error in a working computer is a common thing.

for example memory errors, arithmetic overflows, device errors. etc. All mistakes are

the operating system must make a response that can eliminate the eroor

with little impact on running applications.

6. Accounting (Recording)

The operating system records all usage statistics of various resources and

monitor performance parameters such as response time.

Operating System Processes

Processes in the Operating System contain instructions, program counters, data, processing registers, addresses

delivery, data stack and other supporting variables. For process activities, operating systems

the role is to manage all processes in the system and allocate resources to the process

the. Various processes run simultaneously, where each process gets a part-

memory and control part of its own (SO role), so that each process (program)

has 2 principles below:

1. Independent, these programs are independent, not interdependent

and separate.

2. One program at any instant, is only one process that is served by processors

at one time.

In multiprogramming, the process handling technique is to run a process and

quickly moves to other processes (taking turns), creating a pseudo parallel effect


Process Status

Although each process consists of a separate entity, but sometimes the processes

the process needs to interact with each other. One process can be generated from the process output

others as input.

When the process is executed, a status change will occur. Process status is defined as part

from the process activities that were taking place at the time. Process status consists of:

1. New (the process that is being created)

2. Running (the process that is currently running)

3. Waiting (the process is waiting for several events (events) that will occur)

4. Ready (the process is waiting to be processed by the processor)

5. Terminated (the process has finished running its job (finished executed))

6. Process Control Block ( PCB )

The information contained in each process includes:

1. Process Status : New, ready, running, waiting and terminated.

2. Counter program : Indicates the address of the next command for

run for this process.

3. CPU Registers : Registers vary in number and type depending on

computer architecture design in question. The register consists of

accumulator, stack pointer, index register, general-purpose register, plus code

information in any condition.

4. CPU Scheduling Information : This information contains the priority of a process,

pointer to the scheduling queue, and some other scheduling parameters.

5. Accounting Information : This information contains the number of CPUs and real time ones

used, account numbers, time limits, the number of jobs and processes, and so forth.

6. Input Output Status Information : This information contains a row of input output devices

(such as tape drivers) allocated to the process, rows of files opened,

and so forth.

Operating System Threads

Thread is the smallest unit in a process that can be scheduled by the operating system.

A thread can also be said to be an execution status (ready, running, suspend, block,

queue, etc.). Thread is called a lightweight process. The basic unit of from

system utilization on the processor (CPU). In the thread there are : ID Thread, Program

Counter, Register and Stack. A thread shares a code section, data section and

operating system resources with other threads that have the same process.

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