Secondary Memory

Secondary Memory

Secondary memory (Secondary storage /external memory) differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down because it is non-volatile. It is less expensive than primary storage.

Devices used as secondary memory

Hard disk drive

Hard disks are usually used as secondary storage in modern computers,. The time taken to access a given byte of information stored on a hard disk is typically a few thousandths of a second, or milliseconds and the time taken to access a given byte of information stored in random access memory is measured in billionths of a second, or nanoseconds. hard disks are typically about a million times slower than primary memory.

Optical storage devices

CD and DVD drives used as optical storage devices. They have even longer access times. With disk drives, once the disk read/write head reaches the proper placement and the data of interest rotates under it, subsequent data on the track are very fast to access. As a result, in order to hide the initial seek time and rotational latency, data are transferred to and from disks in large contiguous blocks.

Other examples of secondary storage technologies


Flash memory (e.g. USB flash drives or keys), floppy disks, magnetic tape, paper tape, punched cards, standalone RAM disks and Iomega Zip drives.

For more detail click on following titles   

• Hard Disk 
• Floppy Disks
• Compact Disks
• DVDs 
• Other memory devices 

Activity:

Create a website including more details about following secondary memory devices.

·       Hard disk

·       Floppy disks

·       Compact disks (CD)

·       Digital Versatile disks (DVD)

·       Zip disks

·       Flash drives