This article will explore and clarify a fundamental concept in computers: memory. Because memory is a generic term for “storage device”, we should underscore that – in terms of modern computers – there are two main different types of memory.

Temporary memory

When a technophile references the term “memory”, this is generally referring to the temporary storage space known as RAM. When a program is launched, the contents of that program must be placed into a temporary memory so the processor can interact with it. RAM is known as volatile memory: it must be continuously powered to retain information. Additionally, it is essential to the operation of a computer. The idea of RAM as an all-encompassing word for fast temporary memory is a misnomer, but nonetheless, is common vernacular.

Random-access Memory

Semi-permanent memory

The other major type of memory is hard disk drive (HDD). More recently, a technology known as solid-state disk (SSD) is beginning to replace HDDs, however, they effectively serve the same purpose. Unlike RAM, this semi-permanent storage need not be supplied with continuous power to retain its contents. Therefore, it is known as non-volatile memory. Although included in modern computers, a hard drive is not required for the operation of a computer. One could turn on a computer without a hard drive and load data from another device to operate it as normal. In the past, other devices have acted the part of semi-permanent storage, including floppy disks, magnetic tape, and punch cards.

Hard-disk Drive

The major difference between RAM and HDDs

The main point to emphasize is the trade-off between cost and speed in the two technologies. RAM is much faster than a HDD (by orders of hundreds), but much more costly per unit of space. The introduction of SSDs has closed the speed gap somewhat (at the cost of price), but RAM is still the reigning champion between the two. Additionally, volatility is major condition that affects what data we store in each type of memory. Although a hard drive is not needed to operate a computer, some type of non-volatile memory is required to make the computer useful. This is even true before the operating system (such as Windows, Linux, or OS X) loads. In fact, the initial power-on instructions are stored in a permanent location called CMOS.

Memory: Why?

The prior section contains a basic description of storage in a computer, but the real reason to review it is to understand how each technology is utilized. Because RAM is fast, but volatile, it acts much like short-term memory in humans: the thought (program) is in the forefront of your mind (loaded in RAM), and you can quickly recall information (data) that took place (was stored on disk). Also like short-term memory, if we do not memorize it (commit it to long-term storage), the information is quickly forgotten (erased). Because information is so easily lost when stored in RAM, we are compelled to store important information on a more permanent medium. This is much like having a long-term memory: although the information is stored in your brain (on a hard drive) you can’t act on it (process it) until you actively recall it (read it from disk). Once you are cognizant of that thought (it exists in RAM), you can analyze (calculate) it, supplement (add data to) it, and re-store (save) that changed thought (file).

Wrap-up

If you think of hard drives as long-term memory and RAM as short-term memory, it becomes easy to understand how it isn’t possible to be actively thinking about every single piece of information you ever knew: Most people can only process a couple things at a time, and this is mostly true of computers.