In 1959 Dijkstra published in a 3-page article 'A note on two problems in connexion with graphs' the algorithm to find the shortest path in a graph between any two given nodes, now called Dijkstra's algorithm. Its impact over the next 40 years is summarised from the article of Mikkel Thorup, 'Undirected Single Source Shortest Paths with Positive Integer Weights in Linear Time' (1999): "Since 1959, all theoretical developments in SSSP Shortest Paths for general directed and undirected graphs have been based on Dijkstra's algorithm." Dijkstra's algorithm is used in SPF, Shortest Path First, which is used in the routing protocols OSPF and IS-IS. Various modifications to Dijkstra's algorithm have been proposed by many authors using heuristics to reduce the run time of shortest path search. One of the most used heuristic algorithms is the A* search algorithm (first described by Peter Hart, Nils Nilsson and Bertram Raphael of Stanford Research Institute in 1968), the main goal is to reduce the run time by reducing the search space. Dijkstra thought about the shortest path problem when working at the Mathematical Center in Amsterdam in 1956 as a programmer to demonstrate capabilities of a new computer named ARMAC. His objective was to choose both a problem and an answer (that would be produced by computer) that non-computing people could understand. He designed the shortest path algorithm in about 20 minutes without aid of paper and pen and later implemented it for ARMAC for a slightly simplified transportation map of 64 cities in the Netherlands (so that 6 bits would suffice to represent the city in the algorithm). As he recalled, in an interview published in 2001: