ROM: what is it?

ROM, also called ROM (Read Only Memory) or non-volatile memory, is a memory that stores instructions permanently even in the event of a power outage, unlike random access memory or RAM (Random Access Memory), which stores files temporarily. ROM is used to store immutable information about thecomputer, such as instructions required for booting (BIOS, POST, bootloader or CMOS setup), UEFI firmware or firmware related to peripherals (printer, etc.). ROM is an integral part of motherboard, and it is permanently powered by a small battery.

The access time to ROM is approximately 15 times longer than for RAM (150 nanoseconds against approximately 10 seconds), the latter requiring high execution speed. For speed up startup, certain instructions from the ROM are copied into the RAM during the launch (this is called shadowing or “ghost memory”).

The different types of ROMs

Originally, ROM was read-only and could not be changed by the user. By extension, what is now called ROM is certain erasable, programmable or reprogrammable memories.

• ROM: first generation read-only memory.
• PROM (Programmable Read Only Memory): the “grid” system of fuses to erase them and therefore it can only be reprogrammed once.
• EPROM (Erasable Programmable Read Only Memory): can be erased and rewritten in the presence of high intensity ultraviolet rays.
• EEPROM (Electrically Erasable Read Only Memory): can be erased by a simple Electric power, that is, it can be erased without removing it from the computer. It is the most advanced in read/write capacity but also the most expensive. Removable storage devices flash memory, like the keys USB or SD cards are actually EEPROM type devices.

ROM memory on a phone

On a cellphone or a smartphone, the ROM is none other than the Hard disk storage that integrates the operating system, the apps and files (music, photos, downloads…). On android, it is possible to install a custom ROM (Custom ROMs), stripped of pre-installed applications. It is thus lighter and faster. This also allows you to take advantage of the latest application features even when the manufacturer no longer offers updates.