Computer memory is any physical device capable of storing information temporarily, like RAM (random access memory), or permanently, like ROM (read-only memory). Memory devices utilize integrated circuits and are used by operating systems, software, and hardware.
Volatile vs. non-volatile memory.
Memory can be either volatile and non-volatile memory. Volatile memory is memory that loses its contents when the computer or hardware device loses power. Computer RAM is an example of volatile memory. It is why if your computer freezes or reboots when working on a program, you lose anything that hasn’t been saved. Non-volatile memory, sometimes abbreviated as NVRAM, is memory that keeps its contents even if the power is lost. EPROM is an example of non-volatile memory.
How is memory used?
When a program, such as your Internet browser, is open, it is loaded from your hard drive and placed into RAM. This process allows that program to communicate with the processor at higher speeds. Anything you save to your computer, such as a picture or video, is sent to your hard drive for storage.
Memory is not disk storage.
It is very common for new computer users to be confused by what parts in the computer are memory. Although both the hard drive and RAM are memory, it’s more appropriate to refer to RAM as “memory” or “primary memory” and a hard drive as “storage” or “secondary storage.”
When someone asks how much memory is in your computer, it is often between 1 GB and 16 GB of RAM and several hundred gigabytes, or even a terabyte, of hard disk drive storage. In other words, you always have more hard drive space than RAM.
Types of memory.
There are several different types of memory:
1. RAM (random-access memory):
This is the same as main memory. When used by itself, the term RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost.
2. ROM (read-only memory):
Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to.
3. PROM (programmable read-only memory):
A PROM is a memory chip on which you can store a program. But once the PROM has been used, you cannot wipe it clean and use it to store something else. Like ROMs, PROMs are non-volatile.
4. EPROM (erasable programmable read-only memory):
An EPROM is a special type of PROM that can be erased by exposing it to ultraviolet light.
5. EEPROM (electrically erasable programmable read-only memory):
An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge.
Different types of RAM.
RAM is a bit of a catch-all term, like “memory,” and covers a few different types.“RAM” or “memory” typically refers to dynamic random access memory (DRAM), or more accurately for modern systems, synchronous dynamic random access memory (SDRAM). The terminology doesn’t matter beyond technicalities, but it’s useful to know that the terms are relatively interchangeable colloquially.
▪️The most common type of RAM sold today is DDR4, though older systems may use DDR3 or even DDR2. The numbers denote RAM’s generation, with each successive generation offering faster speeds through greater bandwidth — a higher megahertz (MHz) rating. Each generation also has physical changes, so they are not interchangeable.
▪️Another common term, especially in the video game space, is VRAM (video RAM). Although once a stand-alone piece of technology, VRAM is currently used to denote dedicated memory on the graphics card. For game consoles, it can also reference system memory, but in either case, it has to do with memory reserved exclusively for the GPU. Ram is critical to graphics DDR, or GDDR, usually with a generational designation, like GDDR6.
▪️Most modern graphics cards use GDDR6. However, some graphics cards may use a different VRAM form called High Bandwidth Memory (HBM, HBM2, and HBM2e). It has unique performance advantages, although it is typically expensive, and supply issues hinder widespread adoption.
Vangie Beal, “Memory”، www.webopedia.com
Jon Martindale (24-1-2020), “What is RAM?”، www.digitaltrends.com