Bill Gates was a student at Harvard University and Paul Allen worked for Honeywell in Boston when they saw the Altair computer on the cover of "Popular Electronics". They had previously written software for the earlier Intel 8008 microprocessor and knew the Intel 8080 was powerful enough to support a BASIC interpreter. They sent a letter to MITS claiming to have a BASIC interpreter for the 8080 microprocessor. Roberts was interested, so Gates and Allen began work on the software. Both had experience with the Digital Equipment Corporation PDP-10 minicomputers that they would use. Allen modified the DEC Macro Assembler to produce code for the Intel 8080 and wrote a program to emulate the 8080 so they could test their BASIC without having an Altair computer. Using DEC's BASIC-PLUS language as a guide, Gates determined what features would work with the limited resources of the Altair computer. Gates then started writing the 8080 assembly-language code on yellow legal pads. In February Gates and Allen started using a PDP-10 at Harvard to write and debug BASIC. They also enlisted another Harvard student, Monte Davidoff, to write the floating-point math routines.