Primary and Secondary Memory: RAM, ROM, and More

Primary Memory (Main Memory)

Primary memory holds only the data and instructions on which the computer is currently working. It is generally made up of semiconductor devices. These memories are not as fast as registers. The data and instructions required to be processed reside in the main memory. It is divided into two subcategories: RAM and ROM.

Characteristics of Main Memory:

• These are semiconductor memories.
• It is known as the main memory.
• It is the working memory of the computer.
• It is faster than secondary memories.
• A computer cannot run without primary memory.

RAM (Random Access Memory)

RAM (Random Access Memory) is the internal memory of the CPU for storing data, programs, and program results. It is a read/write memory that stores data until the machine is working. As soon as the machine is switched off, data is erased. Access time in RAM is independent of the address; that is, each storage location inside the memory is as easy to reach as other locations and takes the same amount of time. Data in the RAM can be accessed randomly, but it is very expensive.

RAM is volatile, meaning data stored in it is lost when we switch off the computer or if there is a power failure. Hence, a backup uninterruptible power system (UPS) is often used with computers. RAM is small, both in terms of its physical size and in the amount of data it can hold.

ROM (Read Only Memory)

ROM stands for Read-Only Memory. It is a type of memory from which we can only read but cannot write. This type of memory is non-volatile. The information is stored permanently in such memories during manufacture. A ROM stores instructions that are required to start a computer. This operation is referred to as bootstrapping. ROM chips are not only used in computers but also in other electronic items like washing machines and microwave ovens.

Advantages of ROM

• Non-volatile in nature
• Cannot be accidentally changed
• Cheaper than RAMs
• Easy to test
• More reliable than RAMs
• Static and do not require refreshing
• Contents are always known and can be verified

Secondary Memory

This type of memory is also known as external memory or non-volatile memory. It is slower than main memory. These are used for storing data/information permanently. The CPU does not directly access these memories; instead, they are accessed via input-output routines. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. Examples include hard disks, CD-ROMs, DVDs, etc.

Characteristics of Secondary Memory:

• These are magnetic and optical memories.
• It is known as backup memory.
• It is non-volatile memory.
• Data is permanently stored even if the power is switched off.
• It is used for the storage of data in a computer.
• A computer may run without secondary memory.
• It is slower than primary memories.