What type of computer memory to use in a memory upgrade?

Updated: 11/13/2018 by Computer Hope

Determining the type of memory required

Documentation

Computer memory aka RAMBy far, the best method of determining the memory (RAM) to use with your computer is through the computer or motherboard manufacturer documentation. If you do not have your product documentation, you can also find it online through the computer manufacturers or motherboard manufacturer website.

For example, your motherboard documentation features may list something similar to the example below.

Supports DDR 400/333/266 SDRAM.
Supports up to 3 unbuffered DIMM or 2.5 volt DDR SDRAM.
Up to 1 GB per DIMM with a maximum memory size up to 3 GB.

In the above example, you can see this motherboard supports DDR SDRAM DIMM at speeds of 400, 333, and 266.

Use a third-party tool or service

Another option would be to use a third-party software utility or online service that can provide details about the components in your computer. These utilities can scan your computer and give a detailed report of everything in your computer, including memory. For example, the Crucial System Scanner is a free utility that can scan your computer, and give you details about your installed memory, and about any available memory slots.

Visually examine the memory

512 MB DIMM example of memory stick

Finally, you can also open the computer. Taking precautions not to cause ESD, remove one of the memory sticks and physically examine the memory for any identifying stickers or printed labels.

What to look for in memory

Below is a short list of what you should look for or determine when trying to determine the memory your computer has or needs.

Memory type

What type of memory does the computer use? Some examples of the different memory types include DDR-SDRAM, DDR2-SDRAM, DIMM, DRAM, EDO, FPM, SDRAM, LIMM, RDRAM (RAMBUS), RIMM, SIMM, and SODIMM. Today's computers usually use a variant of DIMM/SDRAM memory.

Amount of pins

How many pins does the computer accept? 72-pin, 30-pin, 168-pin, 184-pin, or 240-pin? The answer depends on the type of memory.

Speed of memory

There are two primary measurements of memory speed.

  • The "speed" of memory generally refers to how many times, per second, the memory can read or change its data per second. This speed is measured in MHz, and strongly affects the overall performance of your CPU.
  • Latency is the (very short) amount of time it takes for memory to respond to an information request, access the data stored in memory, and send that data to the CPU. Latency is measured in nanoseconds (ns).

Although latency is an important metric, differences in latency are relatively minor in compatible RAM modules. When making a decision about what memory to use in your computer, the speed measured in MHz is generally the more important number to consider.

Note

If you install memory sticks of varying speed ratings in your computer, the lower speed will be used, and you will not receive the potential benefit of the faster module's speed. Whenever possible, use RAM modules of equal speed. Ideally, you want all RAM installed in your computer to be identical.

Error-checking

(ECC (error-correcting code) memory is used in servers and professional workstation computers. It sacrifices some of its speed to provide error protection. It quickly checks to make sure there were no errors whenever data is modified in RAM.

Errors may naturally occur in RAM as a result of electromagnetic interference or hardware faults. As a result, bits can become "flipped" in RAM; some bits that should be set to 1 are set to 0, or vice versa. These errors are usually not fatal for casual applications like video games or web browsing. For example, a single pixel in the background of a video game is the wrong value, you might not notice or care. However, for professional applications that require a high degree of accuracy, such as financial transactions or scientific calculations, ECC is a necessary feature. ECC doesn't prevent errors entirely, but it reduces their probably to nearly zero.

Not all motherboards support ECC, and those that support ECC are usually more expensive. The ECC RAM modules are also more expensive than non-ECC RAM of equivalent speed. If you're not sure if you need ECC, you probably don't. Building a computer without ECC support usually means getting more bang from your buck in terms of your computer's performance.

Voltage

What are the voltage requirements? Make sure you determine the voltage requirements of the memory (e.g., 1.8v or 2.5v).

Contact material

The contact material on the memory is also important when considering buying computer memory. The contact area is coated in either gold or tin and should match the material of the memory slots. Mismatching the memory and memory slot contact material can cause corrosion.

Proprietary

Finally, is the memory in your computer proprietary, and if it is not, is there a manufacturer that your computer company recommends? If you have a more recent computer (computer made in the last five years), this should not be a concern.

Other terms

See our memory terms page if there is any other jargon that is confusing you.

Before purchasing memory

Make sure the computer has the available memory slots for the memory you are installing in the computer. For example, if you are installing an additional 1 GB of memory into the computer and plan on using two 512 MB memory sticks make sure you have two available slots. If you do not have available slots, you can remove pre-existing memory and install new memory. However, any memory removed is subtracted from your total. Below is an example of a possible scenario.

Computer memory slots

A computer has 512 MB of memory, from four different 128 MB sticks of RAM and has no more available slots. If you want to upgrade to a total of 1 GB, the four 128 MB sticks would need to be replaced with four 256 MB sticks. Either that, or two of the 128 MB sticks could be replaced by two 512 MB sticks.

Tip

When dealing with memory 1 GB = 1,024 MB

Installing the memory