Features of Memory

  • There are two types of memory, Internal & External.
  • The internal memory is inbuilt in computer memory.
  • It is also known as primary memory. The example of primary memory are registers, cache and main memory.
  • Whereas, external memory is the separate storage device from the computer, such as disk, tape, USB pen drive.
  • Storage capacity can vary in external and internal memory.
  • External devices’ storage capacity is measured in terms of bytes, whereas the internal memory is measured with bytes or words. The storage word length can vary in bits, such as 8, 16 or 32 bits.

Memory can be accessed through four modes of memory.

  • DMA:  Direct Memory Address (DMA) is a method that allows input/output (I/O) devices to access or retrieve data directly or from the main memory.
  • Sequential Access Method: The sequential access method is used in a data storage device to read stored data sequentially from the computer memory.
  •  Whereas, the data received from random access memory (RAM) can be in any order.
  • Random Access Method: It is a method used to randomly access data from memory.
  • This method is the opposite of SAM.
  • For example, to go from A to Z in random access, we can directly jump to any specified location.
  • In the Sequential method, we have to follow all intervening from A to Z to reach at the particular memory location.
  • Associative Access Method: It is a special type of memory that optimizes search performance through defined data to directly access the stored information based on a memory address.
  • The memory devices have a unit of transfer that measures the transfer rate of bits that can be read or write in or out of the memory devices.
  • The transfer rate of data can be different in external and internal memory.
  • Internal memory: The transfer rate of bits is mostly equal to the word size.
  • External memory: The transfer rate of bit or unit is not equal to the word length. It is always greater than a word or may be referred to as blocks.

The performance of memory is generally divided into three parts.

  • Access Time: In random access memory, it represents the total time taken by memory devices to perform a read or write operation that an address is sent to memory.
  • Memory Cycle Time: Total time required to access memory block and additional required time before starting second access.
  • Transfer rate: It describes the transfer rate of data used to transmit memory to or from an external or internal memory device. Bit transfer can be different for different external and internal devices.
  • The  physical type of memory is used in a computer such as magnetic, semiconductor, magneto-optical and optical.
  • The memory can be classified by its physical behaviour like volatile, non-volatile or non-erasable memory.
  • Volatile memory is known as RAM, which requires power to retain stored information, and if any power loss has occurred, stored data will be lost.
  • Non-volatile memory is a permanent storage memory that is used to obtain any stored information, even when the power is off.
  • Non-erasable memory is a type of memory that cannot be erased after the manufactured like ROM because at the time of manufactured ROM are programmed.

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