An operating system (OS) is the software that manages all of the hardware resources associated with your desktop or laptop. The OS performs basic tasks, such as recognizing input from the keyboard, sending output to the display screen, managing files and directories on the hard disk, and controlling peripheral devices like printers.
The OS is a vital component of the system software in a computer system. Application programs like word processors, spreadsheets, web browsers etc. require an OS to function. The OS sits between applications and hardware and makes the connections between all the devices. The OS helps simplify and abstract away all the complexity that goes on in the computer system.
Computer hardware resources including CPU, memory, disk storage and I/O devices can only be managed through the facilities provided by the OS. The OS plays the role of resource allocator and manages how applications utilize these resources. The OS also defines the necessary file systems required for permanent storage capabilities.
Some popular desktop operating systems are Microsoft Windows, macOS and Linux. Mobile and embedded devices run operating systems like Android and iOS designed specifically for those platforms.
The operating system resides on the hard disk drive along with the other files. When the computer is powered ON, the OS is loaded into the computer’s main memory which enables applications to interact with the hardware via features provided by the OS. Let’s take a closer look at how the OS resides on a hard disk.
Components of a Hard Disk
A hard disk drive (or HDD) is the main, and usually largest, data storage hardware device in a computer. The operating system, software applications and data files are stored on the hard disk. The hard disk allows fast access and storage of large amounts of data.
From the outside, a hard disk looks like a metal box containing a stack of platters rotated at a very high speed by an electric motor. These platters are made of non-magnetic materials and are coated with a thin layer of magnetic material. Read/write heads are responsible for writing data to the platters and reading back the data when required.
The OS manages the hard disk using a hierarchical file system. Files are organized into folders called directories. Directories in turn are arranged in a tree-like hierarchy extending all the way from the root directory down. The file system defines rules for naming files, maximum size allowed for files, data structures like file tables to track files and more.
When a file is saved to the hard disk, the OS finds free disk space, reserves the required size, and stores the file contents in that area. The file name and location on disk is stored in a file table for later retrieval. The hard disk is divided into multiple partitions. The OS uses the first partition containing necessary boot files and kernel. This is where the root directory of the disk file system also resides.
The Boot Process
The boot process loads the operating system into memory when a computer is started. Here are the key steps involved:
– The computer starts executing boot code located in the BIOS
– Boot loader code stored on hard disk is loaded into memory
– Boot loader starts loading kernel, the core part of the OS, into RAM
– Once kernel is loaded, it initializes rest of OS subsystems
– Kernel mounts the file system on hard disk
– Kernel starts first process which loads necessary user programs
– User logs in gaining access to OS user interface to run applications
This boot process is controlled by the OS to ensure proper loading of OS components into memory.
Where is the Operating System Located?
The operating system core files are located in specific directories on the hard disk partitioned for OS installation. For example:
– In Windows, OS files are stored in directories like \Windows, \Program files, \Users etc.
– In Linux, OS directories include \usr, \etc, \var, \bin etc.
– Mac OS uses \System, \Library, \Users directories and so on
When the computer boots, the OS kernel is loaded into RAM from the \Windows\System32\ folder in Windows or \boot\ folder in Linux. The kernel remains in memory to manage system hardware and software resources.
Additionally, the root file system containing core libraries and configurations is mounted from the hard disk into memory. The / (root) directory serves as the anchor point for the entire directory tree in Linux systems. In Windows, C:\ typically denotes the root. Mounting the root file system provides access to all other folders and files on disk.
The remaining OS subsystems are initialized with required configurations loaded from specific files and directories on the hard disk. This makes the OS fully operational to serve user requests, execute programs, manage memory and interfaces until shutdown.
Typical OS Directory Structure on Hard Disk
Here is a typical high-level directory structure representing the OS layout on a hard disk:
/ (Root directory)
|___ bin (Binary and executable files)
|___ boot (OS kernel, bootloader)
|___ dev (Device files)
|___ etc (Configuration files)
|___ home (User home directories)
|___ lib (System libraries)
|___ media (Removable media mount point)
|___ mnt (Mount point for local/remote filesystems)
|___ opt (Third party software)
|___ sbin (Essential system binaries)
|___ usr (User utilities and apps)
|___ var (Variable data like logs)
Interaction Between Hardware, OS and Applications
Here is how the major hardware resources like CPU, memory, disk and I/O devices interact with the OS and user applications on a typical computer system:
– CPU executes instructions from multiple applications by scheduling and allocating processor time to each one. The OS facilities like scheduling algorithms and interrupts handle the complexity.
– Main memory is dynamically allocated by the OS when applications need memory. Virtual memory techniques extend the memory available. The OS performs complex memory management.
– Disk drives are formatted with file systems like NTFS, ext4 etc. by the OS. File system driver allows applications to read and write files. The OS handles file storage and lookup of disk sectors.
– I/O devices have device drivers provided by the OS. Devices can be accessed by applications only through I/O APIs defined by the OS.
– Network access, user authentication, access control policies and other security aspects are standardized and implemented by the OS across all applications.
So in essence, the OS abstracts away the complexity of dealing with multiple hardware parts. Well defined interfaces offered by the OS allow smooth communication between applications and hardware resources as required.
Operating System upgrades
Most operating systems periodically release updated versions or new editions with additional features. Individual applications typically remain compatible across OS upgrades. Upgrading the OS can provide benefits like:
– Performance improvements – Faster boot time, increased hard disk throughput etc.
– Support for new hardware – Updated device drivers for new hardware
– Additional features and options
– Reliability enhancements – Bug fixes, security updates etc.
– Better user experience – User interface refinements
OS upgrades require planning for smooth transition without impacting user workflows or application compatibility. New user training may be needed.
Some key steps in OS upgrade planning:
– Review hardware and application compatibility with new OS version
– Schedule appropriate downtime for upgrade steps
– Backup existing data and configurations
– Check for downgrade path if upgrade issues arise
– Deploy OS upgrade to test systems first
– Install OS patches or service packs if available
– Test upgrades thoroughly before production deployment
Overall, the operating system plays a critical role in the functioning of computers. The OS manages resources to meet application and user requirements effectively. Learning about the internal working of the OS provides a deeper perspective into the foundations of computing systems.
Conclusion
In summary, the key points about the operating system residing on the computer’s hard disk are:
– The OS is essential system software managing hardware resources and providing services to applications.
– Critical OS components like kernel, drivers and file system are stored on a partition of the hard disk.
– Boot process loads OS into memory from specific boot files on disk partition.
– Root file system is mounted to provide access to core OS files and user data.
– OS provides well defined interfaces and abstractions to hide low level hardware complexities.
– Upgrading the OS improves features, performance and reliability of the computer.
– Understanding the internal functioning and on-disk structure of an OS gives deeper insight into the computer system.