The Desktop Memory Buyer's Guide: How Much Memory Do I Need?

How to select the proper type and amount of RAM for a desktop PC

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Most computer system specifications tend to list the system memory or RAM immediately following the CPU. In this guide, we will take a look at the two primary aspects of RAM to look at in computer specifications: amount and type.

How Much Memory Is Enough?

The rule of thumb that I use for all computer systems for determining if it has enough memory is to look at the requirements of the software you intend to run.

Pick up the boxes or check the website for each of the applications and the OS that you intend to run and look for both the minimum and recommended requirements.

Typically you want to have more RAM than the highest minimum and ideally at least as much as the highest listed recommended requirement. The following chart provides a general idea of how a system will run with various amounts of memory:

  • Minimum: 4GB
  • Optimal: 8GB
  • Smooth Sailing: 16GB or more

The ranges provided are a generalization based upon most common computing tasks. It is best to check the requirements of the intended software to make the final decisions. This is not accurate for all computer tasks because some operating systems use more memory than others.

Note: If you intend to use more than 4GB of memory on a Windows-based system, you must have a 64-bit operating system to get past the 4GB barrier. More information can be found in my Windows and 4GB or More of RAM article. This is less of an issue now as most PCs are shipping with the 64-bit versions but Microsoft still sells even Windows 10 with 32-bit versions.

Does Type Really Matter?

The type of memory does matter to the performance of a system. DDR4 has been released and is now available for more desktop systems than ever. There are still a lot of systems available that use DDR3 though. Check to see which type of memory is used on the computer as it's not interchangeable and it is vital if you plan on upgrading the memory in the future.

Typically, the memory is listed with the technology used and either its clock speed (DDR4 2133 MHz) or its projected bandwidth (PC4-17000). Below is a chart detailing the order of the type and speed in the order of fastest to slowest:

  • DDR4 3200 MHz or PC4-25600
  • DDR4 2666 MHz or PC4-21300
  • DDR4 2133 MHz or PC4-17000
  • DDR3 1600 MHz or PC3-12800
  • DDR3 1333 MHz or PC3-10600/PC3-10666
  • DDR3 1066 MHz or PC3-8500
  • DDR3 800 MHz or PC3-6400

These speeds are all relative to the theoretical bandwidths of each type of memory at its given clock speed when compared to another. A computer system will only be able to use one type (DDR3 or DDR4) of memory and this should only be used as a comparison when the CPU is identical between the two systems. These are also the JDEC memory standards. Other memory speeds are available above these standard ratings but they are generally reserved for systems that will be overclocked.

Dual-Channel and Triple-Channel

One additional item of note for computer memory is dual-channel and triple-channel configurations. Most desktop systems can offer improved memory bandwidth when the memory is installed in pairs or triples. This is referred to as dual-channel when it is in pairs and triple-channel when in threes.

Currently, the only consumer systems that use triple channel are the Intel socket 2011 based processors which are very specialized. For this to work, the memory must be installed in the correct matched sets. This means a desktop with 8GB of memory will only function in dual-channel mode is when there are two 4GB modules of the same speed or four 2GB modules of the same speed installed.

If the memory is mixed such as a 4GB and 2GB module or of different speeds, then the dual-channel mode will not function and the memory bandwidth will be slowed down somewhat.

Memory Expansion

One other thing that you might want to consider is how much memory the system can support.

Most desktop systems tend to have a total of four to six memory slots on the boards with modules installed in pairs.

Smaller form factor systems typically will only have a two or three RAM slots. The way these slots are used can play a key role in how you can upgrade memory in the future.

For example, a system may come with 8GB of memory. With four memory slots, this memory amount can be installed with either two 4GB memory modules or four 2GB modules.

If you are looking at future memory upgrades, it is better to purchase a system using two 4GB modules as there are available slots for upgrades without having to remove modules and RAM to increase the overall amount.