November 1, 2014

How To Tell If Your Mac Needs More Memory

It’s not always easy to tell if your system needs more memory, or if it’s just slow. In this article, I will present an easy method for even a computer novice to know whether he has enough memory on his Mac!

Virtual Memory and Page Outs

Most people are aware that computers contain at least two different kinds of memory:

  1. Main system RAM is used by running programs
  2. Disks are used for long-term storage

But the lines blur in reality, with modern operating systems able to use disk storage for running applications. Although using disk as memory (a process called paging or virtual memory swapping) allows your system to have effectively infinite RAM, it often slows down performance to an unacceptable level.

Is your system constrained with two little memory, or is it just slow? It can be difficult for the uninitiated to answer this question, but it’s not too difficult to see if your system is swapping excessively: most operating systems will tell you how many “page outs” the system has needed to do, and this is a very strong clue as to whether you have enough memory or not.

Check Activity Monitor in Mac OS X

On Mac OS X, the easiest way to see if you have enough memory is simply to open the Activity Monitor application. You will find this under Applications in the Utilities folder, and it shows you all Certs of useful information about CPU, memory, disk, and network activity.

In Activity Monitor, click on the System Memory tab. At the bottom, next to the pie chart of memory in use, you will see a “Page outs” value. This is the clue you need to know if your system has insufficient memory.

If you have many GB of "Page outs", you should consider getting more RAM!

If you have many GB of “Page outs”, you should consider getting more RAM!

“Page outs” in Activity Monitor shows how much memory has been needed but not available since your system last started up. Since it is much slower than RAM, disk space should be thought of as “overdraft protection” for your system memory. It’s fine to dip into it occasionally, but excessive use will cause trouble!

Reboot, run your system normally for a few days, then check Activity Monitor. There is no hard and fast rule, but if the number is higher than a gigabyte or two over a few days use you ought to consider getting more memory!

What About SSDs?

Fast solid-state storage (SSD) drives reduce the impact of page outs. This is one reason that the meager 2 GB or 4 GB of RAM found in a MacBook Air doesn’t impact performance as much as one would think. This begs the question if SSD-equipped computers need as much system RAM.

Even though SSDs are much faster than hard drives, they are slower than main system memory. And SSDs don’t last forever, so excessive page-outs actually reduce the lifespan of your computer. These are true statements, but should be taken with a grain of salt. After all, a computer only needs to be “fast enough” for the user to be satisfied, and the lifespan of the SSD is probably not as much concern as lifespan of the battery!

It is wise to buy enough system RAM to handle your needs, even if your computer uses an SSD. But it is not as much of a necessity, so don’t fret if you can only buy 4 GB. Personally, I was willing to spend the extra money for 16 GB in my retina MacBook Pro, even though it uses one of the fastest SSDs on the market. But I would have happily bought it with 8 GB if that was not an option, and it will perform great either way.

Stephen’s Stance

In this day of soldered-in system RAM and SSDs, it is difficult to decide what to buy. I recommend checking the page outs on your computer to see how much RAM you really need, then deciding whether to upgrade or buy a new computer with more RAM, especially if you’re using a hard disk drive for storage!

  • Florian

    Nice article!