Types of Storage Devices
Physical components or materials on which data is stored are called storage media.
Hardware components that read/write to storage media are called storage devices.
Two main categories of storage technology used today are magnetic storage and optical storage.
Primary magnetic storage o Diskettes o Hard disks (both fixed and removable) o High capacity floppy disks o Disk cartridges o Magnetic tape
Primary optical storage o Compact Disk Read Only Memory (CD ROM) o Digital Video Disk Read Only Memory (DVD ROM) o CD Recordable (CD R) o CD Rewritable (CD RW) o Photo CD
Magnetic Storage Devices
Purpose of storage devices à to hold data even when the computer is turned off so the data can be used
This scheme simplifies a 2 dimensional set of co-ordinates into a single numeric address.
If the diskette has 80 tracks on each side and each track contains 18 sectors à 1440 sectors per side à 2880 sectors per disk. This configuration is true regardless of the length of the track. The diskettes outermost track is longer than the innermost one but each track is still divided into the same number of sectors. Regardless of physical size all the sectors hold the same number of bytes i.e. the shortest, innermost sectors hold the same amount of data as the longest outermost ones.
A disks allocation of sectors per track is somewhat wasteful because the outer longer tracks could theoretically hold more data than the shorter inner ones. For this reason hard disks allocate more sectors to the longer tracks on the disks surface. As you move towards the disks centre, each subsequent track has fewer sectors. This arrangement takes advantage of the hard disks potential capacity and enables a typical hard disk to store data more efficiently than a floppy disk. Because many hard disks allocate sectors in this manner, their sectors per track specification are often given as an average. Such hard disks are described as having an average of x sectors per track.
Because files are not usually a size that is an even multiple of 512 bytes, some sectors contain unused space after the end of the file. In addition the Windows OS allocates a group of sectors called a cluster to