When DOS was born, popular hard drives only had 5MB or 10MB of storage space, which you could fill today with a single animated GIF.
Most operating systems can read files in these old formats. They tend to use a version of Microsoft’s FAT file format, which dates back to the MS DOS (or IBM PC DOS) operating system used by the IBM PC in 1981. Macs and Windows machines do have their own preferred file formats for internal hard drives, but external hard drives don’t always ship with these pre-installed. The hard drives should not be a problem, unless your computers are very old. However, my Mac doesn’t recognise his hard drive, and his PC won’t recognise my hard drive. I bought a 4TB hard drive for my dad, and thought it would be easy to copy the files over so he could use them on his PC. I have a Mac and an external hard drive that includes some important family files.
