Stack (abstract data type)
In computer science, a stack is an abstract data type that serves as a collection of elements with two main operations:Push, which adds an element to the collection, and
Pop, which removes the most recently added element.
Similarly to a stack of plates, adding or removing is only practical at the top.
The programmable pocket calculator HP-42S from 1988 had, like nearly all of the company's calculators of that time, a 4-level-stack and could display two of four values of the stack registers X, Y, Z, and T at the same time due to its two-line display, here X and Y. In later models like the HP-48, the number of levels was increased to be only limited by memory size.
Friedrich Ludwig "Fritz" Bauer was a German pioneer of computer science and professor at the Technical University of Munich.
Friedrich L. Bauer
Friedrich L. Bauer at the editors' meeting of Informatik Spektrum on 29 May 1995.