DIRECT ACCESS STORAGE DEVICES(DASDs)

The outline secondary storage which is always available to a processor is called direct access storage devices (DASD).The commonly used DASDs are magnetic disks.The optical disks,RAM disks and bubble memory,if incorporated in a system are also DASDs.This term DASD is in the context of permanents type directly accessible long term storage device(i.e.directly accessible secondary storage). As far as the term direct access is connected all semiconductor memories RAMs,ROMs,PROMs are directly accessible and have random access property.Out of these RAMs are for users and they have been categorized as primary memory.In the literature DASDs  are also called ramdom access memory.