You can just say the letters. GIF - Gee, Aye, Eff IOS - Aye, Oh, Ess Mac OS - Mack Oh, Ess Many people say 'GIF' like it's spelled ('giff'), but someone was telling me very recently that the guy who created the file format says it like 'jiff'.

Thanks, Nessy!

For future reference, you can go to www.forvo.com and listen to the pronunciation of any word on there (not just English, but any language). If the word is not on there, you can add it, and a native speaker will voluntarily pronounce it for you. ^^