Primary Storage is referred to as main memory or computer’s internal memory. It is the memory, which is directly connected to the CPU as depicted in Figure 1. It acts as an important part of the computer where the data is stored for quick access by the processor.
You might have come across a term – Random Access Memory (RAM). Primary storage or main memory is called RAM. The main memory comprises large number of cells. Each cell contains a piece of data and is identified by an address called the cell address. Whenever the CPU requires the data, it retrieves it using the cell address. Now, the main memory is designed in such a manner that the time required to retrieve the data from the cell is independent of cell address. In this manner, we can randomly use the location of the memory and for this reason, it is called RAM.
RAM is a volatile type of storage, which means when the system is switched off, you lose the data. The content written or stored in RAM requires power supply to retain the information into the memory.
The two other primary storage areas can be found on the CPU itself: processor registers and processor cache.
Processor Register: As the name suggests, processor registers reside in the processor and are the fastest mode of all computer storage. They can hold the data in 8-bit, 32-bit or 64-bit.
Processor Cache: Cache is the memory that stores the most frequent and commonly used applications of the CPU. This helps in less memory access time and thus, is faster than the main memory. While performing an operation, the CPU checks the processor cache for data, if the data is not found in the processor cache then it accesses the main memory.
All the data is lost from the memory once the computer is switched off, but the data in the computer initiating program called BIOS, used for bootstrapping the computer, cannot be lost. To ensure this, a non-volatile storage was developed known as Read Only Memory (ROM). However, not all types of ROM are just read only, a few can be updated.
Primary storage is internal to the computer and is rigid in size and capacity. There may be scenarios where more storage space is required and an external storage space may be needed to fulfill the storage requirement. Such storage is known as a secondary storage. The following subsection discusses the secondary storage in brief.