Andy founded SUN Microsystems (SUN stood for Stanford University Network) with Scott McNealy (still at SUN) and Vinod Khosla (who had found Daisy Systems, and eventually went to KPCB (Kleiner Perkins Caufield & Byers). Andy had a working piece of hardware and was looking for someone to loan him money to license it. He presented the hardware and opened the opportunity at a Stanford Business School meeting when Scott and Vinod were attending. They convinced Andy that they should instead form a company to sell the hardware. This was the start of SUN. Through and with Vaughn Pratt, a Mathematics professor at Stanford, they contacted Bill Joy and married the hardware with the software Bill had designed (Berkeley's Software Distribution (BSD) of Unix). This became the first desktop Unix running workstation that was addressed at the single user market (Apollo was also making a workstation).
Over the years he was at SUN, Andy made incremental, but fundamental, changes to the SUN workstation line-up. The first real major change came when he directed the development of the SUN SPARC-based, the Sparc-1. This was a collaborative effort that included Dave Patterson, then professor at UC Berkeley, who had directed the educational effort in designing SOAR (Smalltalk On A RISC). Andy realized that SUN needed to find its next technology curve after Motorola had exhausted its 68K based systems on which SUN's systems were based. The SPARC chip set was designed by a team of SUN engineers, and Andy and Dave, to be as scaleable as possible. Still today, more than ten years later, SUN's systems are based on essentially the same architecture.
The most successful system that was developed just before the SPARC-based systems was the SUN 3-60. Andy had designed a system that fit neatly in the palm of the (big) hand. He had proposed to the SUN Microsystems board of directors that the board should be made into a marketable concept. One of the board members asked if the board could be based on the Intel 80386 instead of the Motorola 68030. This became a major issue for Andy and almost left SUN for it. He adapted the board to Sun Federal Systems' division's specifications where it became extremely successful. Based on the success of the Sun 3E, SUN's Marketing decided to adapt it to the general markets, and the result was the Sun 3-60. This was the first time Andy tried to leave and was convinced to stay otherwise. The outcome was that he stayed and designed a system for the Sun Educational Systems Division, specifically, the Sun Sparc-1.
Eventually, after Andy exhausted his experience with the Sparc-1, he left. He designed and founded a company based on a 1 gigabit network card that ran on copper wire (gigabit ethernet). The company was called Granite Systems. He sold the company to Cisco for hundreds of millions of dollars, within a year and a half of when he left Sun.