Definition of Primary Memory

Primary memory is the main memory of computer system. The instructions that have to be currently executed is copied to the primary memory because CPU can directly access the data from primary memory. Accessing data from primary memory is faster as it is an internal memory and processor accesses data from primary memory using data bus.

The primary memory is usually volatile in nature which means data in primary memory does not exist if not saved, in case the power failure occurs. The primary memory is semiconductor memory and is more expensive than secondary memory. The primary memory capacity is limited in computer and is always smaller than secondary memory.

Primary memory can be divided into two types of memory that are RAM(Random Access Memory) and ROM (Read Only Memory).

RAM is a both read and write memory. The data which has to be currently processed is kept in RAM which can be quickly accessed by the CPU. RAM is volatile and loses data if the power is switched off. RAM can be static or dynamic.

ROM is a read only memory; its content can not be altered. It has the instructions that are used when the system is booted up. ROM is a non-volatilememory i.e. it retains its content even if the power is switched off. The types of ROM are PROM, EPROM and EEPROM.

Definition of Secondary Memory

Secondary memory is an auxiliary memory of the computer. The data that has to be permanently stored is kept in secondary memory. The CPU can not directly access the data in secondary memory. The data has to be initially copied to primary memory then only it can be processed by CPU. Hence, accessing data from secondary memory is slower. The secondary memory can be accessed using the input-output channel.

The secondary memory is nonvolatile in nature, which means that the content of the secondary memory exist even if the power is switched off. The secondary memory is magnetic memory or optical memory and it available at cheaperrates as compared to the primary memory.

Secondary memory is available in bulk and always larger than primary memory. A computer can even work without secondary memory as it an external memory. The examples of secondary memory are the hard disk, floppy disk, CD, DVD, etc.