Meaning: The quote you provided is by Dennis Ritchie, a computer scientist known for his pioneering work in the development of the C programming language and the Unix operating system. In this quote, Ritchie is reflecting on the significance of portability in the context of the C programming language and the Unix operating system.

When Ritchie mentions that "C was already implemented on several quite different machines and OSs," he is referring to the fact that the C programming language was designed to be easily adaptable to various hardware platforms and operating systems. This was a departure from many earlier programming languages, which were often tightly coupled to specific hardware or operating systems, making them less portable. The portability of C meant that programs written in the language could be easily transferred from one system to another with minimal modifications, making it a highly versatile and widely adopted language.

The mention of Unix being distributed on the PDP-11 highlights the early roots of the Unix operating system. Unix was initially developed in the late 1960s and early 1970s at Bell Labs, where Ritchie was a key figure. The PDP-11, a popular minicomputer at the time, was one of the early platforms on which Unix was deployed. The fact that Unix was already being distributed on the PDP-11 underscores the growing influence and reach of the operating system at that time.

Ritchie then emphasizes the novelty of the portability of the whole system, referring to the combination of the C programming language and the Unix operating system. The portability of the system meant that Unix and programs written in C could be easily moved across different hardware and operating system environments, enabling a level of flexibility and interoperability that was groundbreaking at the time.

The significance of portability in the context of C and Unix cannot be overstated. This emphasis on portability ultimately contributed to the widespread adoption and enduring influence of both C and Unix. The portability of C allowed it to become a lingua franca for software development, powering a wide range of applications across diverse computing platforms. Meanwhile, the portability of Unix facilitated its proliferation across different hardware architectures, laying the foundation for its enduring legacy as a robust, scalable, and widely used operating system.

In conclusion, Dennis Ritchie's quote underscores the pivotal role of portability in the development and success of the C programming language and the Unix operating system. The emphasis on portability enabled C and Unix to transcend the limitations of specific hardware and operating systems, establishing them as foundational technologies in the history of computing.