Role and Evolution of Operating Systems

CSS Optional — Paper-II, Section-A · P-II.III.I

The OS is examined from two angles that examiners deliberately mix: (1) its role — what job it does for the user and the hardware, and (2) its evolution — how that job changed as hardware got cheaper and users got more demanding. Answer both angles even when only one is explicitly asked, because full marks usually require linking the historical stage to why that stage's OS looked the way it did.

1. Role of an Operating System

An OS is system software that sits between the user/application programs and the computer hardware. It is examined under two complementary views:

Resource Manager view: the OS allocates and reclaims CPU time, main memory, secondary storage, and I/O devices among competing processes, resolving conflicts and enforcing fairness/protection so processes don't interfere with each other.
Extended (Virtual) Machine view: raw hardware is inconvenient and inconsistent to program directly (different disks, different device timings). The OS hides this by exposing a clean, uniform, high-level interface (system calls, file abstractions) — effectively giving the programmer a "better" virtual computer than the physical one.

Concrete responsibilities that follow from these two views: process management, memory management, file system management, I/O/device management, protection & security, and providing the user interface (CLI/GUI) through which humans issue commands.

2. Evolution of Operating Systems

graph LR
    A["1940s-50s<br>Serial Processing<br>(no OS at all)"] --> B["Late 1950s-60s<br>Batch Systems<br>(operator + job queue)"]
    B --> C["1960s<br>Multiprogrammed<br>Batch Systems"]
    C --> D["1970s<br>Time-Sharing<br>Systems"]
    D --> E["1980s-90s<br>Personal Computer /<br>Desktop OS"]
    E --> F["2000s-present<br>Distributed, Real-Time,<br>Mobile, Cloud OS"]

Serial Processing (1940s-50s): no OS existed. Programmers booked machine time, loaded a program via switches/punch cards, and ran it alone. Setup time massively exceeded execution time — the CPU sat idle during loading.
Simple Batch Systems (late 1950s): an operator grouped similar jobs into a batch and a resident monitor (an early, primitive OS) automatically sequenced them, eliminating manual setup between jobs. The CPU still sat idle whenever a job did I/O.
Multiprogrammed Batch Systems (1960s): several jobs are kept in memory at once; when the running job blocks on I/O, the CPU immediately switches to another resident job instead of idling. This is the first real exploitation of CPU/I/O overlap and the direct ancestor of modern scheduling.
Time-Sharing Systems (1970s): multiprogramming is combined with fast, preemptive switching (small time slices) so that multiple interactive users at terminals each get the illusion of their own dedicated, immediately-responsive machine — CTSS and later UNIX are the canonical examples.
Personal Computer OS (1980s-90s): hardware became cheap enough for one user to own a whole machine (DOS, early Windows, Mac OS) — priorities shifted from maximizing CPU utilization (irrelevant with a dedicated single user) toward usability and a graphical interface.
Modern era (2000s-present): distributed OS (resources of networked machines presented as one system), real-time OS (hard timing deadlines, e.g. RTOS in avionics/medical devices), mobile OS (Android/iOS — power and touch-first), and cloud/virtualized OS (a hypervisor multiplexing several guest OS instances on shared hardware).

3. Operating System Services (frequently asked as its own question — "What services does an OS provide?")

Service	What it means
User Interface	CLI (command-line) or GUI through which users issue commands
Program Execution	Loading a program into memory, running it, and handling normal/abnormal termination
I/O Operations	A running program may need I/O involving a file or device — the OS provides the means since users can't control I/O devices directly
File-System Manipulation	Create/delete/read/write files and directories, search, list, manage permissions
Communications	Exchange of information between processes, either on the same computer (shared memory/message passing) or across a network
Error Detection	Constantly monitor for errors — in the CPU/memory hardware, I/O devices, or user programs — and take corrective action
Resource Allocation	When multiple users/jobs run concurrently, resources (CPU cycles, memory, storage, I/O devices) must be allocated to each
Accounting	Track which users use how much and what kinds of resources, for statistics or billing
Protection & Security	Ensure all access to system resources is controlled, and the system is protected from unauthorized access/attacks

The first five (UI, program execution, I/O, file manipulation, communication) exist to make computing more convenient for the user; the last four (error detection, resource allocation, accounting, protection) exist to ensure efficient operation of the system itself — a useful two-bucket way to organize a "list the services" answer for full marks.

4. System Boot (Bootstrapping)

When a computer is powered on, no OS is yet in memory, so a small bootstrap program (stored in firmware — BIOS/UEFI or ROM) runs first. It locates the OS kernel on disk, loads it into memory, and transfers control to it (_start), after which the kernel initializes its data structures, starts the first process (init/systemd on Linux), and the system becomes interactive. This is worth a one-line mention whenever a question asks "how does an OS begin operating" alongside the evolution/role answer.