What does RAM Mean?

RAM, which stands for.Random Access Memory according to abbreviationfinder, is where the computer stores the data it is using at the present time. The storage is considered temporary because the data and programs remain in it while the computer is turned on or is not restarted.

Definition of RAM

It is called RAM because it is possible to access any location of it randomly and quickly. Physically, they are constituted by a set of chips or chip modules normally connected to the Motherboard or Motherboard. Memory chips are black rectangles that are usually soldered in groups to plates with “pins” or contacts:

The difference between RAM and other types of storage memory, such as floppy disks or hard disks, is that RAM is much faster and that it is erased when the computer is turned off, not like floppy disks or hard disks where the information remains recorded.

RAM types

There are many types of DRAM, Fast Page, EDO, SDRAM, etc. In addition there are several names. We will deal with these four, which are the main ones, although there are many more.


  • It is “the original”, and therefore the slowest.
  • Used until the time of 386, its typical speed is 80 or 70 nanoseconds (ns), the time it takes to empty to be able to enter the next series of data. Therefore, the 70 ns is faster than the 80 ns.
  • Physically, it appears in the form of DIMMs or SIMMs, the latter being 30 contacts.

Fast Page (FPM)

  • Sometimes called DRAM (or just “RAM”), since it evolves directly from it, and has been used for so long that they are rarely differentiated. Somewhat faster, both due to its structure (the Quick Page mode) and because it is 70 or 60 ns.
  • Used even with the first Pentiums, physically it appears as SIMMs of 30 or 72 contacts (those of 72 in the Pentium and some 486).

EDO: EDO-RAM or Extended Data Output-RAM

  • Evolves from the Fast Page; allows you to start entering new data while the previous ones are coming out (making their Output), which makes it somewhat faster (5%, more or less).
  • Very common in the Pentium MMX and AMD K6, with a speed of 70, 60 or 50 ns. It mostly installs in 72-pin SIMMs, although it exists in the form of 168-pin DIMMs.

SDRAM or Synchronic-RAM

  • It works in a synchronized way with the speed of the board (from 50 to 66 MHz), for which it must be very fast, about 25 to 10 ns. It only comes in the form of 168-pin DIMMs; it is used in the Pentium II of less than 350 MHz and in the Celeron.

PC100 or 100 MHz SDRAM

  • SDRAM memory capable of operating at those 100 MHz, used by the AMD K6-2, Pentium II at 350 MHz and more modern computers; Theoretically, these are minimum specifications that must be met to function properly at that speed, although not all memories sold as “100 MHz” meet them.

PC133 or 133 MHz SDRAM

  • The most modern and recommended.


This is the way memory chips of whatever type are put together to connect to the motherboard of the computer. They are elongated plates with connectors at one end; the set is called a module.

The number of connectors depends on the data bus of the microprocessor, which is the road through which the data travels rather than a bus; the number of lanes on that road would represent the number of bits of information it can handle at one time.

  • SIMMs: Single In-line Memory Module, with 30 or 72 contacts. Those with 30 contacts can handle 8 bits at a time, so in a 386 or 486, which has a 32-bit data bus, we need to use 4 in 4 equal modules. They measure about 8.5 cm (30 c.) Or 10.5 cm (72 c.) And their sockets are usually white.
  • The more modern 72-contact SIMMs handle 32 bits, so they are used 1 by 1 in the 486; in the Pentium it would be made of 2 in 2 modules (equal), because the data bus of the Pentium is twice as large (64 bits).
  • DIMMs: longer (about 13 cm), with 168 contacts and generally black sockets; They have two notches to facilitate their correct placement. They can handle 64 bits at once, so they can be used 1 in 1 on the Pentium, K6 and higher. They exist for standard (5 volts) or reduced (3.3 V) voltage.

And we could add the SIP modules that were similar to SIMMs but with fragile soldered legs and that have not been used for many years, or when all or part of the memory is soldered on the board (in the case of some brand computers).

Other types of RAM

BEDO (Burst-EDO)

Evolution of the EDO, which sends certain data in “bursts”. Little widespread, it competes in performance with SDRAM.

Memories with parity:

They consist of adding to any of the previous types a chip that performs an operation with the data when they enter the chip and another when they leave. If the result has changed, an error has occurred and the data is no longer reliable.

Said like that, it seems like an advantage; however, the computer only warns that the error has occurred, it does not correct it. Moreover, these errors are so unlikely that most chips never suffer from them even if they have been working for years; For this reason, all the memories have been manufactured without parity for years.


Memory with error correction. It can be of any type, but especially EDO-ECC or SDRAM-ECC. Detects data errors and corrects them; for really critical applications. Used on servers and mainframes.

Video Memories

For graphics cards. From lowest to highest performance, they can be: DRAM -> FPM -> EDO -> VRAM -> WRAM -> SDRAM -> SGRAM.

DDR-SDRAM: (Double Data Rate)

DDR-SDRAM Operation

It consists of sending the data 2 times for each clock signal, once at each end of the signal (the upstream and downstream), instead of sending data only on the upstream part of the signal.

In this way, a device with DDR technology that operates with a “real”, “physical” clock signal, for example 100 MHz, will send as much data as one without DDR technology that operates at 200 MHz. DDR device clocks are usually given in what we could call “effective or equivalent MHz” (example, 200 MHz, “100 MHz x 2”).

One of the problems with Rambus memory: it runs at “physical” 266 MHz or higher, and is very difficult (and expensive) to manufacture.

DDR technology is in fashion lately, under this or another name. In addition to the many graphics cards with DDR-SDRAM video memory, we have for example the AMD Athlon and Duron microprocessors, whose 200 MHz bus is really “100 x 2”, “100 MHz with double signal utilization”; or the AGP 2X or 4X, with 66 MHz “physical” used twice or four times, since a graphics card with a 266 MHz “physical” bus would be difficult to manufacture… and extremely expensive.

(Attention, this does not mean that an AGP 4X card is actually twice as fast as a 2X, far from it: sometimes they “feel” just as fast, for reasons that are not relevant now.)

Well, DDR-SDRAM is the DDR concept applied to SDRAM memory. SDRAM is none other than the well-known PC66, PC100 and PC133, the memory that is currently used in almost all normal PCs; the 133 MHz of the PC133 is already a difficult thing to surpass without raising the prices much, and therefore the introduction of the DDR.

DDR-SDRAM types and nomenclature

Of course, there are DDR memory of different classes, categories, and prices.

The first, it can work at 100 or 133 MHz (again, “physical”); something logical, since it is SDRAM with DDR, and the SDRAM works at 66, 100 or 133 MHz (by the way, there is no DDR at 66 MHz). If we consider the “equivalent” MHz, we would be facing memories of 200 or 266 MHz.

In the first case it is capable of transmitting 1.6 GB / s (1600 MB / s), and in the second 2.1 GB / s (2133 MB / s). At first they were known as PC200 and PC266, following the MHz classification system used with SDRAM. But Rambus arrived and decided that his memories would be called PC600, PC700 and PC800, also according to the MHz system.

As this would make them appear much faster than DDR (which does not happen, because they work in a completely different way), it was decided to name them according to their transfer capacity in MB / s: PC1600 and PC2100 (PC2133 is not commercial, so viewed).

How much memory should I have?

Until before 1996 the cost of memory had remained a constant cost of around US 40 per megabyte. By the end of 1996 prices had dropped to US 4 a megabyte (a 901% drop in less than a year). Today RAM is less than US 1 per megabyte.

The amount of RAM required is solely a function of what a computer is used for, which determines which operating system and programs are to be used, a minimum amount of 64 MB of RAM is recommended, and if possible even 128.

How much memory is enough?

In the world of computers, the question always seems to be whether to buy an Intel or AMD microprocessor, whether it will be a Pentium III or an Athlon, a Celeron or a K6-2, and how many MHz it will work. When it comes to memory, most buyers accept the default quantity, which can be a big mistake.

The most important thing when buying a computer is that it is balanced; nothing at 800 MHz for just 32MB of RAM, or a high-end 3D card for a small, poor-quality monitor. And as we will try to demonstrate, the amount of memory on the PC is one of the factors that can affect performance the most.

By the way, this work will focus on Windows 95 and 98, as they are by far the most widely used operating systems. The results are perfectly applicable to Linux, “except” for its greater stability and better use of memory; As for Windows NT 4 and 2000, they act in a similar way to Linux, although they consume between 16 and 40 MB more memory than “home” Windows.

Windows and virtual memory

Of course, the more programs we use and the more complex they are, the more memory we will need; This is sure not to surprise anyone, but what may surprise us is the large amount of memory that is used just to boot the operating system. Look at the following data:

Amount of memory used
Loaded programs RAM used
Windows 95 only 21 MB
Windows 98 only 27 MB
Windows 98 only, after several months of operation and several program installations 35 MB
Windows 98, Microsoft Word 97 and Internet Explorer 4 46 MB
Windows 98 and AutoCAD 14 (with a simple 2D drawing) 55 MB

As you can see, just loading the operating system can consume all of the memory that some low-end computers are sold with. Additionally, Windows 98 uses more memory than Windows 95 due to, among other things, its integration with Microsoft Internet Explorer. To finish complicating the issue, both Windows tend to increase their size and memory consumption as we install programs, or simply as time passes, without installing anything.

Despite this, the fact is that computers continue to work when their RAM memory runs out, something that would be impossible if it were not for the so-called “virtual memory”, which is nothing but hard disk space that is used as if it were memory. RAM.

However, this virtual memory has several drawbacks; the main one is its speed, since it is much slower than RAM. While RAM access speed is measured in nanoseconds (ns, 0.000000001 part of a second), hard drives are measured in milliseconds; in other words, it takes almost a million times longer to access a piece of data found on the hard disk than it does from the RAM.

Therefore, the ideal is to need virtual memory as little as possible, and for that obviously you have to have as much RAM as possible.

Upgrade RAM

Identify the type of memory your computer uses. The most appropriate source of information in this regard is the motherboard manual, although in general:

  • 386
  • DRAM or FPM in 30-pin SIMM modules, about 100 or 80 ns
  • Hard-to-find memory, uninteresting update
  • 486 slow
  • FPM on 30-pin, 80 or 70 ns SIMM modules
  • Typical of DX-33 or lower speeds
  • 486 fast Pentium slow
  • FPM on 72-pin, 70 or 60 ns SIMMs, sometimes alongside 30-pin modules
  • Typical of DX2-66 or higher and Pentium 60 or 66 MHz
  • Pentium
  • FPM or EDO on 72-pin, 70 or 60 ns SIMM modules
  • Pentium MMX AMD K6
  • EDO in SIMM modules with 72 contacts, 60 or 50 ns
  • Celeron Pentium II up to 350 MHz
  • 66 MHz SDRAM on 168-pin DIMMs, less than 20 ns
  • They usually also support PC100 or PC133; also in some K6-2
  • Pentium II 350 MHz or more Pentium III AMD K6-2 AMD K6-III AMD K7 Athlon
  • 100 MHz SDRAM (PC100) on 168-pin DIMMs, less than 10 ns
  • Still widely used; usually also support PC133
  • Pentium III Coppermine (533 MHz or higher) AMD K7 Athlon AMD Duron
  • 133MHz (PC133) SDRAM on 168-pin DIMMs, less than 8ns, the most widely used memory today

Tips for buying memory

First, its size: nowadays no one in their right mind should install less than 64 MB, with 128 MB being much better or even more if it is 3D CAD or graphic design. As for the type: SDRAM or RDRAM (Rambus DRAM)? Without a doubt, always SDRAM; the Rambus is very expensive and its performance is only slightly higher.

Once we have decided on SDRAM, let’s choose its speed: the most demanding SDRAM memory is PC133 (SDRAM at 133 MHz) necessary to mount modern Pentium III computers with 133 MHz bus and Athlon on KX133 board. Ask for this speed and pay whatever it is (usually just a little more); even if you don’t need it for now (in the case of Celeron, K6-2, most of Athlon…) it will allow you to upgrade in the future.

Unfortunately, the memories are not all compatible with each other, especially the modules larger than 128 MB; There are modules that go perfectly on one board and on another they don’t even start. If you can, choose brand name memory: Kingston, Samsung, Micron, HP… although you cannot consider it a guarantee either; the best, buy in the same place plate and memory, making sure that it is a trustworthy site


As we have seen, the appearance of electronic computers is quite recent, and it has had a dizzying advance. So much so, that nowadays the competition between the computer producing companies has caused the appearance of new models with very short periods of time, which are sometimes months. What causes an increase in: the speeds of the processors; storage capacities; bus transfer speed; and so on.

The aforementioned has required memory manufacturers to constantly update them, exceeding themselves time and again in speed, capacity and storage.

Currently the market is gaining momentum again, due to the appearance of very fast processors, which work at speeds of 1 GHz.

At the present time, it seems that the most reasonable thing for the vast majority of users is to install PC133 SDRAM memory, both for its excellent quality / price ratio and for its proven compatibility.

This memory should be the option chosen for any micro that we are going to install, since the price difference with the PC100 is very scarce and although now we do not take full advantage of it (if we install it in a Celeron, Athlon or a Pentium III with bus 100MHz), in the future it will give us more expansion possibilities.

Taking this into account, if you are going to install a micro Intel, the most recommended chipsets for the motherboard would be the VIA Apollo Pro 133 / 133A, for all its modern capabilities but mainly for its PC133 support. In the case of boards for the AMD Athlon K7, the best would be the VIA KX133; If we cannot find motherboards with this chipset (it is not yet widely implemented), we should at least install PC133 to be able to expand in the future.

The 820 chipset boards are not at all recommended, due to their high price and poor performance with SDRAM memories. Of course, if you can afford to install Rambus memory of the PC800 class, you will notice a certain increase in performance, but you better invest the difference in buying a better graphics card, a faster hard disk, more memory or a micro with a few MHz more.

As for the now classic BX chipset, it may not be the best buy for a new motherboard, but its performance with 100 MHz bus mics is frankly high and can be an excellent compromise until newer chipsets arrive., especially on boards prepared for overclocking. Of course, as long as you can install PC133 memory (or at least branded PC100).

In the near future, it is to be expected that Intel chipsets based on the 820 but prepared to support PC133 (the so-called Intel 815) will finally appear, in addition to the first developments with support for DDR-SDRAM memory (probably on chipsets from VIA and AMD), which will allow transfers between 1.6 and 2.1 GB / s. And perhaps even the Rambus memory will drop in price dramatically and become a viable option.

Observing the events that have happened throughout the evolution of memory, we can assume that it will continue to grow in terms of speed, capacity and decreasing the physical space occupied.