Differences Between RAM and ROM

There are several types of memory storage in computers, including RAM, ROM, magnetic HDD, SSD, and plug-in external storage devices like SD cards, Blu-ray disks, and USB drives.

Two of these types, RAM and ROM, sound almost alike, yet these two types of memory have quite different definitions, characteristics and purposes. Let’s look in-depth.


RAM is the fastest as well as the most expensive type of memory in a computer. Is RAM permanent storage? No, RAM stores data only temporarily. Another major characteristic of RAM is that RAM data can be easily modified.

In contrast, ROM does provide permanent storage. Some – but not all – types of ROM now allow data to be erased and rewritten, though not nearly as efficiently as RAM.

RAM and ROM do share some traits in common, though. Each supplies a crucial kind of internal memory needed for a computer to function properly. Also, RAM and ROM are both located on the computer motherboard, but in separate plug-in chipsets.

To learn more about the many differences and similarities between RAM vs. ROM, read on. Here is more information about types of computer memory.


Both RAM and ROM contain sub-divisions with different variations on the core technology.

What is RAM?

What is RAM memory used for? Essentially, the function of RAM is to store the data that the CPU needs for running for the operating system, software programs, and processes.

RAM’s speed is measurable in nanoseconds. Because it is so blazingly fast, RAM can switch rapidly between tasks.

RAM capacity on a computer generally ranges from 64MB to 4GB, in comparison to merely 4MB to 8GB for ROM. RAM capacity is provided through RAM chips, which fit into two to four memory slots located next to the CPU on the computer motherboard.

To add more capacity, you can upgrade the RAM chips on your computer, but you need to make sure that the new chipset is compatible. For example, it isn’t enough to insert DDR3 RAM into a DDR3 socket. You must use DDR3 RAM with a speed acceptable to the computer.

RAM as a Volatile Memory

Is RAM volatile or nonvolatile? RAM is volatile memory, meaning that it only stores data while the power is switched on. When the computer is turned off, the data in RAM gets automatically erased.

Due to RAM’s volatile memory, all work done on a computer is constantly saved on the hard drive so that data won’t be lost in case of a sudden interruption in power supply.

How Does RAM Function?

RAM is also read-write memory, meaning that the CPU is able to quickly read instructions from RAM and write results to RAM, rapidly modifying data.

RAM is called random access memory because the computer can directly access and manipulate RAM memory randomly, in any order, and from any physical location.

How does random access memory work? Basically, RAM is a semiconductor placed on a processor which stores variables for CPU calculations. RAM supplies memory locations for requested data. The CPU gets a data read instruction with the data’s memory address or location and then sends the address to the RAM controller.

The controller, for its part, transmits the address to the proper pathway, opening path transistors and reading each capacitor value. Ultimately, the read data is transmitted back to the CPU.

What are the Types of RAM?

The two main types of RAM memory are Static RAM (SRAM) and Dynamic RAM (DRAM).

SRAM is a memory chip that is faster and requires less power than DRAM.  More costly than DRAM, SRAM is generally used by the computer as cache memory. SRAM uses the state of a six-transistor memory cell to store a bit of data. Typical SRAM speeds are between 20 nanoseconds (ns) and 40 ns.

DRAM is a memory chip that can hold more data than an SRAM chip, although it is slower and needs more power. It uses a DRAM memory cell made up of a paired transistor and capacitor to store a bit of data. In contrast to SRAM, each DRAM cell must be periodically refreshed because capacitors tend to leak power. Typical DRAM speeds are between 60ns and 100ns.

What is ROM?

Read only memory (ROM) provides permanent storage for instructions needed during bootstrapping, or the process of turning on the computer. It does so by storing the BIOS and other firmware for the computer hardware. This firmware is very hardware-specific and rarely needs updating.

The firmware contains the basic code to start up the computer. On most modern computers, the read-only memory is located on a BIOS chip which plugs into the motherboard.

Aside from computers, ROM is also used in calculators, peripheral devices, and embedded systems for which programming needs aren’t expected to change. Previously, ROM chips were used in game cartridges for early gaming machines, such as the original Nintendo and Gameboy.

ROM as a Non-Volatile Memory

Is ROM volatile or nonvolatile? ROM is non-volatile memory, meaning that it stores data both while the power is on and when the power is switched off. Unless ROM gets erased, it never forgets data.

How does ROM Function?

The CPU can read data in ROM. Traditionally, it hasn’t been possible to modify the data in ROM. Some ROM chips now have rewrite capabilities, and data can be erased from several types of ROM. However, data can’t be rewritten or erased nearly as quickly and easily as with RAM.

How does ROM work during bootstrapping? When you press the power button, the BIOS chip awakens and checks the various components of the computer to make sure they are all present and working correctly.

In a process known as the power-on self-test (POST), the BIOS instructs the CPU to start checking code at different locations. During the test, you might hear the whirring of the hard drive and see some flashing lights. After the test is finished, the CPU takes over and launches the operating system.

What are the Types of ROM?

The three main types of ROM storage are as follows: Programmable ROM (PROM), Erasable and Programmable ROM (EPROM), and Electrically Erasable and Programmable ROM (EEPROM).

  • PROM is a type of ROM which is manufactured as blank memory, such as in a CD-ROM. Data is written after manufacturing.
  • EPROM is a ROM chip that can be erased by exposing the chip to high-intensity ultraviolet rays. EPROM can then be reprogrammed.
  • EEPROM data can be erased electrically using field electron emission, also known as Fowler–Nordheim tunneling, an easier process than the one used in EPROM. EEPROM can then be reprogrammed approximately 10,000 times.

Differences between RAM and ROM

Jacqueline Emigh
Jacqueline Emigh
Jacqueline Emigh (pronounced "Amy") is a veteran tech journalist, with literally thousands of published articles to her credit. She is currently a columnist for Internet.com, as well as a frequent writer for a number of other leading magazines and Web sites. She was previously a senior editor at Ziff Davis Media's Sm@rt Partner Magazine. Before that, Jacqueline spent seven years as a bureau chief for Newsbytes News Network, a daily newswire specializing in computer technology. Her work has been translated into dozens of languages.

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