Feb 22 2025
APIs, or Application Programming Interfaces, are tools that let different software talk to each other. They began in the 1950s with work by Maurice Wilkins and David Wheeler on the EDSAC computer, creating libraries of reusable code. Their 1951 book, "The Preparation of Programs for an Electronic Digital Computer", was a key early text, showing how to use these libraries, which is like an early version of APIs.
The term "API" first appeared in 1968 in a paper called "Data structures and techniques for remote computer graphics" by Ira W. Cotton and Frank S. Greatorex. It described how applications could interact with graphics systems, marking the start of APIs as we know them today.
In the 1980s, Unix introduced system calls, which were standardized APIs for tasks like file management. This made software more portable across different computers. Windows also developed its own APIs, like the Windows API, helping developers build programs for that platform.
The 1990s brought the internet, and with it, web APIs using technologies like XML-RPC and SOAP for machine communication. In the early 2000s, Roy Fielding's REST approach simplified web APIs, using HTTP methods like GET and POST. This made APIs easier to use and led to their widespread adoption.
In the 2000s, companies like Amazon with S3 and EC2, and Google with Maps, started offering public APIs. These allowed developers to build on their services, sparking cloud computing and innovation. For example, Amazon's APIs helped create the cloud infrastructure we use today, while Google's Maps API let apps show locations easily.
It's surprising that early APIs, like those in the 1960s, were mainly about hardware, such as graphics systems, rather than the software connections we see today. This shows how APIs evolved from physical to digital interactions.
The history of Application Programming Interfaces (APIs) is a fascinating journey that reflects the evolution of computing and software development. From their nascent beginnings in the mid-20th century to their pivotal role in today's digital ecosystem, APIs have transformed how software systems communicate and integrate. This survey provides a detailed exploration of key milestones, innovations, and their impact, offering a strict superset of the information in the direct answer section.
The concept of APIs can be traced back to the 1950s, with significant contributions from British computer scientists Maurice Wilkins and David Wheeler. They worked on the Electronic Delay Storage Automatic Calculator (EDSAC), one of the first computers to use a stored-program design, operational by 1949. For EDSAC, they developed a modular software library stored on punched paper tape, accompanied by a "library catalog" that documented how to use each subroutine. This catalog is considered an early form of API documentation, as it instructed programmers on integrating these subroutines into larger programs.
Their seminal work was published in 1951 in the book "The Preparation of Programs for an Electronic Digital Computer", which is often cited as the first book on computer programming. This text detailed the use of a library of 88 subroutines for mathematical operations, emphasizing reusability and modularity. While the term "API" was not used, the principles laid the groundwork for future interface designs.
The term "API" itself emerged in the 1960s, specifically in 1968, with the paper "Data structures and techniques for remote computer graphics" by Ira W. Cotton and Frank S. Greatorex, presented at the AFIPS Fall Joint Computer Conference. This paper described the interface between application programs and graphics systems, using FORTRAN-type subroutine calls to ensure hardware independence. This marked the formal recognition of APIs as a means for applications to interact with system services, focusing initially on computer graphics.
The 1980s marked a significant period of standardization for APIs, driven by the rise of operating systems like Unix. Unix, developed in the 1970s and gaining prominence in the 1980s, introduced a set of system calls that acted as APIs for tasks such as file manipulation, process control, and inter-process communication. These system calls provided a consistent interface across different Unix implementations, enhancing software portability and modularity. For example, the C Standard Library, integral to Unix, offered APIs for input/output processing, abstracting hardware complexities ("The design of the Unix operating system").
Other operating systems followed suit. Microsoft Windows, emerging in the 1980s, developed the Windows API (WinAPI), which provided functions for creating graphical user interfaces and interacting with operating system services. This standardization was crucial for the software industry, enabling developers to build applications that could leverage system capabilities consistently, fostering a rich ecosystem of software.
The advent of the World Wide Web in the early 1990s revolutionized API usage, shifting focus to network-based communication. Initially, web APIs relied on technologies like XML-RPC and Simple Object Access Protocol (SOAP), which facilitated remote procedure calls over HTTP. These were primarily machine-to-machine interactions, often complex due to their reliance on XML documents and remote procedure calls, as noted in discussions on SOAP's challenges ("A brief history of Web APIs").
A pivotal change occurred in the early 2000s with Roy T. Fielding's introduction of Representational State Transfer (REST) in his 2000 doctoral dissertation, "Architectural styles and the design of network-based software architectures". REST provided a simpler, standardized approach, leveraging HTTP methods (GET, POST, PUT, DELETE) to manipulate resources identified by URLs. This simplicity and alignment with web principles led to the widespread adoption of RESTful APIs, transforming web service design.
The 2000s also saw the rise of public APIs from major technology companies. Amazon launched its Simple Storage Service (S3) API in 2006 and Elastic Compute Cloud (EC2) in 2007, enabling developers to build on cloud infrastructure ("Amazon S3 API"). Google followed with APIs for services like Google Maps, allowing embedding of maps and location features in applications ("Google Maps Platform"). X (formerly Twitter) introduced its API in 2006, enabling access and manipulation of tweets, fostering a vibrant ecosystem of third-party applications ("Twitter API"). These public APIs catalyzed the API economy, where companies leveraged APIs for innovation and revenue generation.
The evolution of APIs has had a profound impact on software development, enabling distributed systems, microservices, and the Internet of Things. The proliferation of mobile devices in the 2010s led to mobile-specific APIs, allowing applications to access device hardware and services. New standards like GraphQL have emerged, offering flexible data querying, while API security and governance have become critical as APIs handle sensitive data.
This survey highlights the continuous adaptation of APIs, from hardware-focused interfaces in the 1960s to the network-centric, developer-friendly tools of today. Understanding this history provides context for current practices and insights into future developments, ensuring APIs remain at the forefront of technological advancement.