||May 1996 Volume 12:6
Rightsizing your mac application memory
By Kristin E. Nelson
Machine lockups, warnings about not enough memory to open applications,
or problems opening large or complex documents can be
symptomatic of a low memory situation. If the amount
of installed memory (RAM) on your Macintosh is sufficient to handle your
computing needs, you can use this memory more efficiently by rightsizing the memory
allocations to the applications you use.
Before experimenting with different memory allocations, consult each
application's user manual and other information available from the software
developer for memory usage tips. Arriving at the
proper memory amounts for your applications and work
style requires some trial and error but can be well worth the effort.
About This Macintosh
To optimize Macintosh application memory alloca
tions, start by consulting the About This Macintosh
window over the course of several typical computing
sessions - when the applications that you often have open
at the same time are in fact open. Click on your desktop
to make the Finder active and then select About This
Macintosh from the apple menu to view information about the machine's current
The window displays the following information:
The list of applications in the lower part of the
window tells you how much memory has been reserved
for each open application (and cannot therefore be
used by other applications). The shaded section shows
how much of this allocated memory is currently in
use by the application. Turn on balloon help and move
the cursor onto the shaded bar to see the numeric equivalent.
- Built-in Memory. The amount of RAM physically installed in the machine.
- Largest Unused Block. The largest block of memory
available to launch another application.
- Total Memory. The RAM (physical + virtual memory) available
to the Macintosh. (Note: This item displays only when virtual memory
is on or when a memory utility, such as RAM Doubler, is installed.)
Use the Get Info box to view and modify the current
memory settings for your individual applications. Before
you can modify settings in the Get Info box for an
application, you will need to quit the application if it is
currently running. Locate the application you want to
modify, highlight its icon, and then select Get Info from
the File menu. (Note: Find the application's icon, not
The Memory Requirements section of the Get Info
box provides the following information:
- Suggested size. The memory allocation recommended
by the application's developer.
- Minimum size. The smallest unused block of memory
that must be available for the application to launch.
- Preferred size. The maximum RAM allocated to the
application if a block larger than the minimum size is
available. (Note: MacOS versions prior to 7.1 used
the single setting "current size" in place of the minimum and preferred
Use the information gathered from the About This
Macintosh window to modify the settings available in the
application's Get Info window. You can change both the
minimum and preferred memory sizes but you cannot set
the minimum size larger than the preferred size.
What you change in the Get Info window depends
on the situation you want to correct.
When changing memory allocations, remember that
you are still working within the confines of the largest
unused block of memory on your computer and that less
memory may be available for other programs. Monitor your memory situation
for a few days before and after changing the allocations. If you find you
encounter more problems after changing memory settings, return them to
the previous values and investigate other possible causes
such as extension conflicts, software in need of updating,
or hardware problems.
- If the application freezes often or if you need to load
large or complex documents that require additional
memory, try increasing the application's preferred size.
If extra memory is available, it will be allocated to this
program. (Note: When increasing application
memory, a good starting point is to increase by 50
percent. For example, set an application currently
using 2,000 KB to 3,000 KB).
- If you do not want to run the application with anything
less than a specified amount of memory, increase the
minimum memory setting as well. For example, if you discovered that for
your purposes an application requires a certain amount of memory, change the
minimum setting to that amount. (Note: Use the rule
of thumb above as a general guideline for increasing
the minimum memory setting.)
- If you find that an application allocates much more
RAM than you typically use or if you don't have much
memory left in the largest unused block to launch the
application, try reducing its preferred and/or minimum
memory allocations. Be careful! Lowering the memory requirements may cause
more frequent low memory situations and application crashes.
Other memory tips
Rightsizing your applications is a good strategy
for optimizing the memory you have, but when it
comes to memory, the more RAM you can install, the
better. Here are a few additional tips about memory management.
- If you've opened and closed applications throughout
the day, your available memory may be fragmented into a number of smaller chunks.
The largest unused block is the largest of these memory chunks and may
be insufficient to open another application. Exiting all
open applications, or better yet, restarting your machine, will clear out the
memory and should provide a larger unused block of memory for your application.
- If your Macintosh has a 68030 CPU or better or a 68020 CPU with a PMMU chip,
use virtual memory to provide a memory boost by increasing your total
memory and thus the largest unused block. To set virtual memory, which uses
space on your hard drive as additional RAM, open the Memory control panel. Turn
Virtual Memory on and then click the up or down arrow (shown below) to set an
amount for total RAM (i.e., physical RAM + virtual RAM). This amount will
be taken away from available hard drive space so make
sure you can afford to lose this storage space. Be
aware, however, that virtual memory creates overhead
by accessing the hard drive and can slow machine performance in certain situations.
- On a Power Macintosh, turn on virtual memory to
reduce the memory requirements of native applications
(those designed to run on a Power Macintosh). Increasing the memory by 1 MB
provides the benefits of Power Macintosh memory management without the
additional overhead of higher settings.
- If you use virtual memory on any Macintosh, do not
exceed twice your physical RAM and keep the amount
reasonable. Increasing your RAM by 50 percent is generally a reasonable
- Some software applications work better with real
(physical) memory as opposed to virtual memory. A
number of applications (including Adobe Photoshop)
use their own memory management scheme. In these cases, using virtual memory
decreases the performance of the application.
KRISTIN E NELSON is a Consultant for ISC's Computing Resource Center.