Introduction to Memory

The term memory applies to any electronic component capable of temporarily storing data. This article will explain the different categories of memory, the technical characteristics of memory and the differences between Flash Memory, Read-Only Memory and Random Access Memory.



The Different Categories

There are two main categories of memory:

  • Internal memory: it temporarily memorises data while programs are running. Internal memory uses micro conductors, i.e. fast specialized electronic circuits. Internal memory corresponds to what we call random access memory (RAM).
  • Auxiliary memory: is also called physical memory or external memory). Its role is to store information over the long term, including after the computer is turned off. Auxiliary memory corresponds to magnetic storage devices such as the hard drive, optical storage devices such as CD-ROMs and DVD-ROMs, as well as read-only memory.

Technical Characteristics

The main characteristics of a memory are:

  • Capacity: represents the global volume of information (in bits) that the memory can store.
  • Access time: corresponds to the time interval between the read/write request and the availability of the data.
  • Cycle time: represents the minimum time interval between two successive accesses.
  • Throughput: defines the volume of information exchanged per unit of time, expressed in bits per second.
  • Non-volatility: characterises the ability of a memory to store data when it is not being supplied with electricity.

The ideal memory has a large capacity with restricted access time and cycle time, a high throughput and is non-volatile.

However, fast memory is also the most expensive. This is why memory that uses different technologies are used in a computer, interfaced with each other and organized hierarchically.

Access time and capacity of the different types of memory


The fastest memory is located in small numbers close to the processor. Auxiliary memory, which is not as fast, is used to store information permanently.

Types of Memory

Random Access Memory

What is Random access memory ? It is the system's main memory, meaning it is a space that allows you to temporarily store data when a program is running.

Unlike data storage on an auxiliary memory such as a hard drive, RAM is volatile, meaning that it only stores data as long as it is supplied with electricity. Thus, each time the computer is turned off, all the data in the memory are irremediably erased.

Read-Only Memory

What is read only memory ? This type of memory, also called ROM, is a type of memory that allows you to keep the information contained on it even when the memory is no longer receiving electricity. Basically, this type of memory only has read-only access. However, it is possible to save information in some types of ROM memory.

Flash Memory

What is flash memory? It is a compromise between RAM-type memory and ROM memory. Flash memory possesses the non-volatility of ROM memory while providing both read and write access. However, the access times of flash memory is longer than the access times of RAM. You can also use a flash memory card.

Photo: Unsplash

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