What does "would" mean here?
Good question! "Would" here is used as a modal verb to express future tense as told in the past. You can express future in the past tense by using "would + verb". Both "woulds" in this sentence mean "was going to". You can think of this sentence as, "as it was going to develop into what was going to become the operating system for nearly every PC." Here's a few examples of future in the past with "would": Ex: I knew you would give it to him. Ex: I thought you would eat the chicken.