On April 13, 1909 was born Stanislaw Ulam. He is a mathematician who did early theoretical work on the use of computers in mathematics. Ulam teaches at Harvard and the University of Wisconsin before joining the Manhattan Project in Los Alamos, New Mexico, where he meets John von Neumann. There, Ulam and von Neumann discuss using computers to understand questions of pure mathematics. Based on the ENIAC experience, Ulam suggested to von Neumann that neutron diffusion and related chain reactions were natural applications and just as quickly outlined a procedure to implement the notion.
Source: https://www.computerhistory.org/tdih/april/13/#mathematics-pioneer-ulam-born
On April 14, 2000 died Phillip Walter Katz. He was a computer programmer best known as the co-creator of the Zip file format for data compression, and the author of PKZIP, a program for creating zip files that ran under DOS. A copyright lawsuit between System Enhancement Associates (SEA) and Katz’s company, PKWARE, Inc., was widely publicized in the BBS community in the late 1980s. Phil Katz’s software business was very successful.
Source: https://en.wikipedia.org/wiki/Phil_Katz#PKARC_and_PKWARE
On April 15, 1977 the first West Coast Computer Faire begins, introducing personal computers, in both kit and assembled form, to a new audience – the general public. It was an important year for personal computing as three of the most popular personal computing systems of all time were announced then: the Apple II, presented by then-21-year-old Steve Jobs and Steve Wozniak, the Commodore PET, and the Radio Shack TRS-80. The Faire, held at the San Francisco Civic Auditorium & Brooks Hall, exposed tens of thousands of enthusiasts and the curious to a coming revolution in computing that would change all of our lives. The first Faire is one of the most significant events in the history of personal computing.
Source: https://www.computerhistory.org/tdih/april/15/#first-west-coast-computer-faire-begins
On April 16, 1959 the programming language that provided the basis for work in artificial intelligence, LISP, has its first public presentation. Created by John McCarthy, LISP offers programmers flexibility in organization and it or its descendants are still used in the AI development environment.
Source: https://www.computerhistory.org/tdih/april/16/#lisp-language-unveiled