When to Use (or Not Use) a RAM Disk


08-23-00 - In the semi-early days of the Macintosh (1992-1998), there was great competition between Mac users as to who could hack their machine into running faster, better, and cooler-looking. One of the greatest ways to speed things up, for actual work or for play, was to create a RAM disk and work on the file from the RAM disk rather than the much slower hard drive.

Now, it's pretty easy to turn on a RAM disk, but learning when to use it, and when it is not necessary or will cause problems, is another matter entirely.

The most common use of a RAM disk now is for users who want to surf the Web more quickly than normal. They turn on the RAM disk and place the browser's cache in it. This speeds things up because, again, RAM is faster than the hard drive.

It used to be that graphics professionals would place the image they were working on (say in Photoshop), on the RAM disk to speed things up. With the advent of greater amounts of RAM, many people are putting the application in the RAM disk as well. Okay, I can see how people might want to do this and think that it works pretty slick.

So, what is the point of this already? Well, I'm getting to it.

How many people who use a RAM disk are actually aware of certain issues, such as what size work best, and when it could create problems?

Size

Make sure that the size of the RAM disk is not more than the amount of memory left over from the System and any applications you want to have running while you use it. Doesn't leave you a lot of room, does it? For example, I have 256MB of RAM on my machine (the 8600s have 96, and the G3s have 192, and the new G4s have 384).

My system takes up 39.9 MB (! Yikes, I have some optimizing to do!). I have to have Photoshop, PageMaker, and Illustrator open at the same time, and possibly Netscape and Dreamweaver. So, a RAM disk of about 50MB may work fine. If I try to use all 256MB, I would be in deep trouble (as in having to boot-from-CD-to-get-my-machine-to-work-again trouble).

Lately, I have seen a disturbing trend in the use of RAM disks in the labs. I have seen RAM disks that have been set to use all of the available memory, leaving the system nothing to enable it to even boot up. I have seen students leave the RAM disk on when restarting which causes MAJOR problems with MacAdmin, especially the "Save on Shutdown" checkbox option.

So, I have a few tips for you that may make your life, and WILL make my job easier.

1. If you absolutely have to use a RAM disk (99.9% of you will not), make sure to set the disk to no more than the minimum required to hold the application and the files (like the Netscape Cache folder). If you set this too high, you will cause the machine to crash at startup the next time you reboot.

2. Do not use the "Save at Shutdown" option. Make periodic backups of your file by dragging a copy from the RAM disk to the hard drive. "Save at Shutdown" will cause the machine to lock at startup. If this happens, the only way for me to fix it is to startup from CD, and fix the problem manually (this takes awhile).

3. Do not ever-ever-ever use a RAM disk with Virtual Memory enabled. Virtual Memory uses disk space as memory. The goal of a RAM disk is to use RAM as disk space to boost speed. It is counterproductive to use Virtual Memory in combination with a RAM disk.

Virtual memory side-note:

When setting virtual memory, which you should not have to do on our new machines, it is best to either set it to 1MB over the built-in RAM, or double it. Setting the virtual memory to fill the entire available drive space is not a good idea - it leaves you no room to save or work with files in any application.

Now that I have shared how and why you may use a RAM disk, I am going to let you in on a little secret.

Machines in the lab are fast enough, with special, AV-rated hard drives, that you will never really find a need to use a RAM disk. Back in the days of the Quadras and the IIci (blazingly fast 40 and 25 MHz processors!) it was very necessary. Today, with the G3 and G4s dual processor machines, it is not necessary (all you MacAddicts out there - I feel your pain at admitting this, but am glad for the new speeds).

So, you now you know reasons for using a RAM disk, some guidelines, and reasons you really don't need to use one. Hopefully, this article has cleared up some confusion about the amazingly critical, all-powerful, it slices-and-dices, RAM disk question!

–J

Jennifer Nieland is the lab coordinator for the College of the Design student computer labs. Watching the RAM disk icon fly by as she shuts down a machine is very annoying and causes toes to hurt from kicking the wall.