Basics Of Operating System

What Is an Operating System?

Computers don’t directly understand human languages. All they understand is binary machine language (0s and 1s). But for humans, it’s extremely difficult to communicate with computers in that form. Software programs are the interfaces between humans and computers that help both to communicate with each other easily. There are two categories of software:
system software and application software.
An operating system is
the system software that helps manage and coordinate all hardware and software resources. Common tasks include device management, multitasking, user management, memory allocation, and so on. The operating system also provides a base or foundation for the execution of other application software. Some of the most widely used operating systems are Microsoft Windows, Linux (Red Hat, Fedora, CentOS, Ubuntu, AIX, BSD, and others), and Android/iOS for smart phones and tablet PCs. The operating system plays a crucial role from the security perspective. However, secure the application may be, if the underlying operating system is vulnerable and unpatched, then it becomes a soft and easy target for hackers and intruders. Hence, from a defensive as well as an offensive perspective, it is important to familiarize yourself with the basics of an operating system and get acquainted with various security features that the operating system offers. The following sections briefly discuss some of these features.


What Is a Kernel?

In simple words, the kernel is the core of the operating system. It has full control over all the activities that occur in the system, and it is the first program that is loaded on startup. A few of the important tasks performed by the kernel are memory management, device management, and managing system calls. The kernel does the critical job of connecting and interfacing application software with the hardware devices.

The Ring Architecture

For fine-grained security, operating systems implement a concept called protection rings, as shown in Image below. The ring levels are classified based on their respective access privileges. The kernel, which is the core of the operating system, is at Ring 0 and has the highest privilege, meaning it has full and complete control of all computing resources (hardware and software).
   
                                               

Image. The ring architecture of an operating system

The higher the ring level, usually the lower are the privileges. The application software that is installed as an add-on has the least system access privileges because it can’t be trusted easily. The operating system tries to protect the ring boundaries; however, from a security perspective, nothing can be more dangerous or harmful than an attacker executing a malicious code/program with kernel-level privileges (at Ring 0).

What Is a File System ?

A file system defines how data will be stored or retrieved from the storage devices. There is various file systems available; they differ in various factors like the size of data to be allowed for storage, their directory structure, naming conventions, method of buffering, and so on. Some of the common file systems in use are listed in Table.

Operating System

File Systems Used

Microsoft Windows

FAT16, FAT32, NTFS

Linux and its derivatives

EXT2, EXT3, EXT4, XFS, ReiserFS, YAFFS

MAC OS

HFS+


Table. Types of File Systems Used by Various Operating Systems

What Are Device Drivers ?

While the file system helps in storage and management of data, an operating system also needs an interface for interacting with various types of devices that are attached to the system, such as audio/video devices, gaming devices and so on. Device drivers are a special type of software program used for interfacing between the hardware device and the operating system. Whenever we plug in a new hardware device, the operating system detects it and starts looking for a suitable device driver. Most contemporary operating systems have a set of common device drivers for various hardware devices. There are some hardware devices whose device driver is not present in the operating system by default; in such case the device driver can be installed from the media (CD/DVD) supplied with the device. Some malicious programs even try to modify device drivers to get unauthorized control over the system

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