Secondary memory is permanent memory. It is not directly accessible by CPU. It communicates with the CPU through the main memory. Secondary memory stores data and holds it even when power is off. It is used to store large amount of data or programs. It is less expensive than the primary memory.
Pen Drive:
A pen drive is a portable universal serial bus (USB) flash memory device. It is used to store and transfer audio, video and data files from a computer. The major advantage of USB pen drives over other portable storage devices such as floppy disks or DVDs/CDs is their compact shape and size; they work faster and can store more data.
