ROM memory – Concept, uses and types of ROM

We explain what ROM memory is and what this type of storage is for. Also, the types of ROM and what is RAM.

ROM memory
ROM is used for read only.

What is ROM memory?

In computing, when we talk about ROM memory (acronym for ReadOnly Memory, that is, Read-Only Memory), we refer to a type of storage used in computers and other electronic devices, which is characterized by being only accessible for reading and never for writing, that is, it can be recovered but not modified or intervened.

ROM memory is sequential access and its presence is independent of the presence of a power source. As has been said, its content cannot be modified, or at least not in a simple and everyday way, and usually contains information entered into the system by the manufacturer, of a basic, operational or primary type.

This type of memory also operates in a much slower than its counterpart, RAM (acronym for Random Access Memory, that is, Random Access Memory), so its content is usually dumped in the latter to run faster.

There are, however, versions of ROM memory (known as EPROM and Flash EEPROM) that can be programmed and reprogrammed multiple times, despite the fact that its operation is governed by the same rules as the traditional one. However, as their reprogramming process is infrequent and relatively slow, they continue to be called in the same way.

What is ROM for?

ROM has two main uses, which are:

  • Software storage. Commonly, computers in the 1980s brought their entire operating system stored in ROM, so that users could not mistakenly alter it and disrupt the operation of the machine. It is still used today to install the most basic startup or operating software (BIOS, SETUP, and POST, for example).
  • Data storage. Since users do not usually have access to a system’s ROM, it is used to store data that will not require any modification in the life of the product, such as look-up tables, mathematical or logical operators, and other technical information.

ROM memory types

The EPROM can be erased when exposed to ultraviolet light or high voltage levels.

Let’s consider three different types of ROM memory:

  • PROM. Acronym for Programmable ReadOnly Memory (Programmable Read Only Memory), is of the digital type and can be programmed only once, since each memory unit depends on a fuse that burns when doing so.
  • EPROM. Acronym for Erasable Programmable ReadOnly Memory (Erasable Programmable Read Only Memory) is a form of PROM memory that can be erased when exposed to ultraviolet light or high voltage levels, erasing the information contained and allowing it to be replaced.
  • EEPROM. Acronym for Electrically Erasable Programmable Read-Only Memory (Electrically Erasable and Programmable Read-Only Memory) is a variant of EPROM that does not require ultraviolet rays and can be reprogrammed in the circuit itself, being able to access the bits of information individually and not together.


Unlike ROM, RAM is much faster and freely writable. This means that all running programs go to this memory bank, but strictly temporary: when shutting down or restarting the system, the entire RAM memory is cleaned. This does not mean, of course, that the information saved on disk is lost, but only that in execution.

RAM memory is today extremely efficient, fast and economical, which is why many systems engineers prefer to make use of it instead of ROM.