2: History and evolution

2: History and Evolution of Operating Systems

Understanding the evolution of operating systems (OS) reveals how core concepts developed to address fundamental hardware limitations and user needs. Early computers (1940s-1950s) operated without any OS. Programmers interacted directly with the hardware using machine language, manually loading programs via punched cards or tape. This "bare machine" approach was incredibly inefficient: the CPU sat idle during lengthy setup (loading programs, mounting tapes) and I/O operations, wasting expensive compute time – a problem known as the human operator bottleneck.

To improve CPU utilization, simple batch systems emerged (late 1950s). Operators collected similar jobs (batches) and fed them sequentially to the computer using a resident monitor – a small, permanently stored program acting as a rudimentary OS. This monitor automatically loaded the next job from tape when the current one finished, reducing setup time. However, CPU idleness persisted during slow I/O operations as jobs couldn't overlap.

Multiprogramming (early 1960s) tackled this idleness. It allowed multiple jobs to reside in main memory simultaneously. When one job performed I/O (a slow operation), the OS scheduler could immediately switch the CPU to execute another ready job. This overlapping of CPU and I/O operations dramatically increased throughput and CPU utilization. It required crucial OS advancements:

• Memory management to protect jobs from each other
• CPU scheduling algorithms for job selection
• Rudimentary synchronization

The demand for interactive computing led to time-sharing (mid-1960s). Pioneered by systems like CTSS and MULTICS, time-sharing extended multiprogramming by rapidly switching the CPU between multiple interactive user terminals. Each user received small, frequent CPU time slices, creating the illusion of dedicated access. This required:

• Sophisticated scheduling
• Memory protection
• Concurrent access to file systems

It directly supported the rise of multi-user systems.

The UNIX OS (1969, Bell Labs) embodied these principles elegantly. Its modular design, written in C (not assembly), emphasized:

• Simplicity
• Portability
• Powerful command-line tools piped together

UNIX became the foundation for many modern systems (Linux, macOS).

The personal computer revolution (late 1970s/1980s) shifted focus to single-user, cost-effective systems. Early PC OS like CP/M and MS-DOS were simpler, initially lacking features like multiprogramming or memory protection. The graphical user interface (GUI), popularized by Apple's Macintosh (1984) and Microsoft Windows, made computers accessible to non-technical users, emphasizing user experience over raw throughput.

Modern OS evolution continues, driven by:

• Networking (distributed systems, the Internet)
• Mobile computing (iOS, Android – focusing on touch interfaces, power management, security)
• Virtualization (running multiple OS instances on one machine)
• Cloud computing (OS services delivered over the Internet)