If you check Wikipedia, it defines Steampunk as “a sub-genre of science fiction that typically features steam-powered machinery, especially in a setting inspired by industrialized Western civilization during the 19th century. Steampunk works are often set in an alternative history of the 19th century’s British Victorian era or American ‘Wild West’, in a post-apocalyptic future during which steam power has regained mainstream use, or in a fantasy world that similarly employs steam power.” 
So, while science fiction typically looks forward, or at least looks at now with a scientific bent, steampunk is looking back – looking back at possibilities and alternatives. And, in some rare cases, it maybe looking at now but from a historical perspective, again with the alternative of more mechanization instead of computerization.
This brings us to Vintage Tomorrows: A Historian And A Futurist Journey Through Steampunk Into The Future of Technology
. Note that this is a new and updated edition of his book that was published in 2008.