When using your Mac, active programs, documents, and system resources
will be loaded into memory (RAM), where they can be accessed quickly to
run and perform computations. While active memory contents are
maintained in memory, the system also keeps some recently used but
inactive processes and data there in order to quickly revive them, if
These memory allotments should be managed dynamically for optimum
performance, but some people who regularly run low on RAM may be
concerned about this and resort to using “RAM cleaning” programs. One of
these is the “purge” Terminal command that is installed along with
Apple’s Xcode developer tools. If you find yourself regularly using
these programs, then you might wonder whether this is necessary — and
even healthy for the system.
MacFixIt reader Paul recently wrote in with such a question:
I have only 4 gigs of stock RAM, and the possibility of
upgrade in future. Clearing up my RAM cache in terminal by running
“purge” at least once a day is getting frustrating. Is it a must to open
up terminal and/or to run a purge? Last time I checked it showed about
800 megabytes of usable RAM. Also, is it safe to use the machine with
less than 800 megabytes RAM, without any harm to the computer?
Having a low levels of free RAM will not harm your system at all, and
will only reduce its capacity to open more items. However, if you are
regularly running low on memory, even though programs like “purge” may
show an immediate increase in free RAM, this change is only temporary
and will not help the system optimize RAM usage. In fact, it may even
show a small hit on performance.
The purge command and other memory cleaning routines simply bypass
the system’s automatic memory management and clear out unused RAM
contents manually, sometimes doing so by putting a large, temporary load
on the system to stress the RAM usage and squeezing the memory
footprint of other programs to be as small as possible.
When you run this utility, you will see the green “free memory”
portion of the memory chart in Activity Monitor get larger, suggesting
more RAM is now available. However, while this technically does result
in more RAM being designated as “free,” it is only a temporary measure
since the system and programs will progressively load this data back
into RAM again, only now being bottlenecked by the hard drive’s slower
speed and therefore will run a bit slower than usual during this time.
To give an analogy of this process, consider RAM as the tabletop of a
desk on which you work. If the table is empty then there is space for
you to put the equipment you need for your job — pens, papers, books,
and other tools analogous to applications you use in a computer.
However, if the table is smaller, you cannot put as many items on it, or
if you do you will have less overall space on which to work.
This is the same for computers, where if you load many programs,
widgets, and system tools, then the space remaining to do work will be
more limited, especially if you have only a limited amount of RAM to
Using commands like “purge” is like shoving all of your pens, papers,
and books into a tight pile in one corner of the desk, and even putting
some into the desk drawers to clear as much of the tabletop as
While doing this technically gives you more room in which to work, to
get things done you may need to sift through the pile and spread its
contents out again. This is what happens with the computer: after
running “purge,” when you access various programs they will simply
spread out and reclaim the RAM that you freed up.
Therefore, if you are constantly running low on memory and are seeing
regular slowdowns as a result, then upgrade your RAM (to at least
double your current amount, especially if you currently have only 4GB)
instead of running memory cleaning routines. Getting more RAM for your
system would be like getting a table top extension for your desk, so the
computer can “spread out” your work, be more efficient, and run at