Computer Memory - Computer Fundamentals

What is computer memory? How does it work?

Computer data is stored in the form of memory. It contains memory which works just like a human brain. It helps to store data and instructions that are to be processed before execution. Computer memory is the storage space, where the data is to be processed. This computer memory is divided into large number of small parts called cells. Each location or cell has a unique address, which differs from zero to memory size minus one. For example, if the computer has 64k words, then this memory unit has 64 * 1024 = 65536 memory locations. The address of these locations varies from 0 to 65535.

Memory is primarily stored in three types −

  • Cache Memory
  • Primary Memory/Main Memory
  • Secondary Memory

Cache Memory

Cache memory is considered as a very high speed semiconductor memory which can speed up the CPU. It acts as a buffer between the CPU and the main memory. It helps to store the data and program which is used by the CPU more frequently. The parts of data and programs are transferred from the disk to cache memory by the operating system, from there the CPU will access the data.

cache_memory

Advantages

The advantages of cache memory are as follows −

  • Cache memory is faster than main memory.
  • It consumes less time for accessing as compared to the main memory.
  • it stores the programs and executes within a short period of time.
  • It stores data for temporary use.

Disadvantages

The disadvantages of cache memory are as follows −

  • Cache memory has limited capacity.
  • It is very expensive.

Primary Memory (Main Memory)

Primary memory is nothing but stores the data and instructions on the computer which is currently working. This memory has a limited capacity and data is lost when power is switched off i.e it stores the data for temporary use. It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction that need to be processed resides in the main memory. It is divided into two subcategories RAM and ROM.

primary_memory

Characteristics of Main Memory

  • These are semiconductor memories.
  • It is known as the main memory.
  • Usually volatile memory.
  • Data is lost in case power is switched off.
  • It is the current working memory of the computer.
  • Faster than secondary memories.
  • A computer cannot be run without the primary memory.

Secondary Memory

This type of memory is also known as external memory or non-volatile. It is very slow compared to the main memory. This memory stores the data and instructions permanently that is to be executed. Hence it is called permanent storage memory. Accessing these memories does not take place directly by the CPU, 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. For example, disk, CD-ROM, DVD, etc.

secondary_memory

Characteristics of Secondary Memory

  • These are magnetic and optical memories.
  • It is known as the backup memory.
  • It is a non-volatile memory.
  • Data is permanently stored even if power is switched off. It can’t be erased.
  • It is used for storage of data in a computer.
  • Computer can work in the absence of secondary memory.
  • Very slow as compared to primary memory.

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