The Genesis of Personal Computer Operating Systems

The journey of personal computing is rich with fascinating milestones, and at the heart of this legacy is the first operating system designed for personal computers. This journey encompasses the rise of CP/M, Apple DOS, and the evolution of operating systems that provided the foundation for today's computing landscape.

An Innovation from the Early '70s

The first operating system specifically designed for personal computers was CP/M (Control Program for Microcomputers), developed by Gary Kildall in the mid-1970s. CP/M quickly became the standard for early personal computers, including those based on Intel's 8080 and Zilog's Z80 microprocessors. It provided a robust platform for running software applications and managing hardware resources, significantly influencing the personal computing market.

Early Contenders and Their Roles

Although CP/M dominated, other contenders like Apple DOS played important roles. Apple DOS was utilized by the Apple II series starting in 1978. However, CP/M is widely recognized as the first widespread operating system for personal computers. GM-NAA I/O, established in 1956, was a far earlier system but not specifically designed for personal computers as we know them today.

From SOLOS to CP/M

Back in 1976, the author mentions running SOLOS on a small PC, which used cassette tapes for storage. The IMSAI also had an operating system that the author did not run, while ISIS, from which CP/M was derived, was designed for larger systems. The author also mentions a keyboard monitor, though it may not be considered an OS in the strict sense, as they were running one by 1973.

The De Facto Standard: CP/M and Beyond

CPM, or CP/M, was a significant step forward, often associated with the S-100 bus. The S-100 bus was not a computer but rather an expansion bus for systems like the Altair 8800, which used the Intel 8080 CPU. Prior to CP/M, personal computers were often hobbyist kits that required extensive assembly and wiring, making them unsuitable for mass consumers.

The Leap to Personal Computing

The Apple II, Commodore PET 2001, and TRS-80 were collectively referred to as CP/M systems, and while they didn't quite fit the modern definition of an operating system, they allowed users to load programs from disks and perform basic disk management. CP/M itself was slightly more advanced, offering features like directory listings, file renaming, and basic file management, which were essential for a user-friendly computing environment.

Migrating to IBM and Beyond

PC-DOS, the OS for the IBM PC, was derived from QDOS, which in turn was derived from CP/M. When the IBM PC was first released in 1981, it ushered in a new era where IBM PCs became the industry standard. CP/M's command-line interface was patterned after Digital Equipment Corporation's (DEC) operating systems, such as RT-11 for the PDP-11 and OS/8 for the PDP-8.

Legacy and Evolution

Key commands in CP/M included DIR (directory), ERA (erase file), REN (rename file), SAVE, TYPE, and USER. Transient commands like DDT (debugger), DUMP (dump memory), ED (editor), LOAD, MOVCPM (move files), PIP (pipe files), and STAT (status) were also part of the suite. The system allowed users to add additional transient commands, essentially programs, extending its functionality.

Reflections on Early Computing

The author fondly recalls their experience with an early Apple II, noting that its 32KB of RAM and 4-color display were impressive in their time. The Apple II, while lacking a built-in disk drive initially, could save programs to cassette tapes, a process that could be achieved using any portable audio cassette player. Although the Apple II didn't have a disk drive, it eventually gained one, enhancing its capabilities.

The Journey of Computing

Reflecting on the early years, the author shares how owning an Apple II helped them develop valuable programming skills and eventually transition into a career focused on computer science. From a 6700 dollar investment (in 2021 terms) to today's powerful laptops with advanced hardware, computing has come a long way. The journey from these early systems to today's sophisticated technology is a testament to the evolution of human ingenuity and technological advancement.