text: Speed is usually measured in BAUD or BITS..more commonly measured in BITS. Functonality depends on what you are talking about..are you talking about hard disk I/O or RAM or Bus ?  Importance...well compatability issues arise or perhaps memory or disk speeds that are too slow will create traffic jams and lock up your system.\n\nBasically, the speed or I/O measures the ability of a device to read and write data.