George R.R. Martin began writing the "Song of Ice and Fire" series of fantasy novels back in 1991, and, based on a recent interview with Conan O'Brien, he's been using the same technology to write books ever since.

While Martin maintains a computer for updating his blog and filing his taxes, he told the late-night TV host that his "secret weapon" is an offline DOS machine that runs WordStar 4.0, a word processing program from the 1980s.

"It does everything I want a word processing program to do, and it doesn't do anything else," he said of WordStar, noting that when he wants a capital letter he can find the shift key. Martin also expressed his frustration with the spellcheck feature in modern applications, which may have something to do with him writing 1,000-page books littered with names like "Daenerys Targaryen."

You can watch the exchange here:

Martin discussed his technology choices in a Q&A last year.