TITLE
    PowerBook: Setting Up to Run from a RAM Disk
Article ID:
Created:
Modified: 		12259
6/4/93
7/13/98
TOPIC

    I have two PowerBook computers and would like to use the RAM Disk. One computer has 64 MB of RAM installed and the other has 24 MB. Can you provide suggestions for effective use of the RAM Disk for each computer? Can I use the RAM Disk on desktop computers?

DISCUSSION

    1) Make sure that you have about 10 MB of free space on the PowerBook hard disk (install space), and also about 3 MB to 4 MB as permanent backup for the RAM Disk. Have a current System Folder already installed on your internal hard disk.

    2) It's best to have a full 8 MB of RAM in your PowerBook. You can use a RAM Disk with 6 MB, but it's usually too awkward.

    3) Use the Memory control panel to create a 4 MB RAM Disk. Later, you should increase or decrease the RAM Disk size depending on your particular circumstances. The trade-off is between the size of the RAM Disk and the amount of memory remaining to run system software and applications. A 3.2 MB RAM Disk seems to be optimal.

    4) Install a minimal system on the RAM Disk with your System installation disks.

    5) Copy selected items manually back into your System Folder. These items are optional. The more that you copy back, of course, the less space is available on your RAM Disk for applications and documents. The objective is to get everything you need onto the RAM Disk and avoid powering up the hard disk. You will need to fine-tune your setup to suit your circumstances. You'll at least want to copy back Chooser, Startup Device, Portable or PowerBook, and Battery.

    Examples of what you might copy to the RAM Disk System Folder include:

    Alarm Clock, LaserWriter, Memory, AppleShare (not File Sharing), and a few fonts. Additional third-party items are: SAM Intercept, SCSI Probe, and the PowerBook File Assistant's Assistant Toolkit extension.

    6) Select up to three applications you want to put on the RAM Disk. Keep only the application and the accessory files you really need.

    7) Leave at least 200K to 300K free for documents and other files. Even better is 400K to 500K, because things like Preference files and other items often take additional space.

    8) In addition, regularly copy documents in progress to the hard disk as a backup. This takes only a second, and the hard disk doesn't stay powered very long. Just after doing such a copy, put the PowerBook to sleep with the Sleep Fkey (available as part of the PowerBook File Assistant software), and then rewake it just so the hard disk will sleep sooner.

    9) Leave your PowerBook in sleep mode all the time so that the RAM Disk is always around and ready to run. Shutting down erases the RAM Disk on many of the PowerBook models. Restarting is OK.

    NOTE: The Persistent RAM Disk feature of PowerBook File Assistant software allows information in the RAM Disk to be saved between restarts and shutdowns.

    If you switch batteries while your PowerBook is asleep, MAKE SURE THE POWERBOOK IS PLUGGED IN AND GETTING POWER, otherwise your RAM Disk will be erased! When on the road and far from a power outlet, back up your entire RAM Disk to the hard disk when the first or second (not the third and final!) battery warning comes on. Then shut down, switch the batteries, reboot, copy the RAM Disk contents back, and continue computing.

    The RAM Disk on the PowerBook 100 survives shutdowns and you can switch the main battery while in sleep mode without the power supply plugged in, since the 100 has a secondary set of batteries. There's a slight battery drain when in sleep, but a PowerBook seems to be able to last a few weeks in sleep mode.

    10) If your PowerBook crashes, use a paper clip to push to the restart button. The RAM Disk will usually be intact if you do this. You can use the on/off button to restart the crashed PowerBook if you don't mind losing the contents of your RAM Disk and recreating it from your hard disk copy.

    11) Use the Startup Device control panel to select which disk to start from (RAM Disk or internal hard disk). Switch between running the System Folder on the hard disk and the minimal System on the RAM Disk. Use the RAM Disk just when you want to be power conscious.

    12) Put your PowerBook to sleep whenever possible. From the Battery control panel of Special menu you can put the PowerBook to sleep. If you have the PowerBook File Assistant installed, use the Sleep Fkey (Shift-Command-0) to instantly put the PowerBook to sleep whenever needed (no need to switch to Finder and select Sleep). Wake up is instantaneous if you have AppleTalk turned off and are running from a RAM Disk.

    If possible, upgrade the amount of built-in RAM. System 7.1 requires 8 MB of built-in RAM. Higher Mac OS versions require more RAM to use the RAM Disk.

    Files run faster when they are stored on and run from the RAM Disk instead of accessing files on a hard drive which has slower access time.

    Reducing the Virtual Memory setting or turning it off completely will speed up RAM Disk performance.

    Storing applications in the RAM Disk will improve the speed of those applications. Remember, many applications store resource files or folders at different locations on the hard drive and those resources may run slower than expected when accessed, including spelling checkers.

    Allocate enough RAM to the RAM Disk to store the System Folder with the minimum necessary extensions and applications. To increase RAM Disk speed, do not use aliases in the System Folder if you have enough built-in RAM to assign to the RAM Disk.

    The RAM Disk must be set large enough to store the Finder, System, Assistant ToolBox (System 7.1 through System 7.5.5), and if necessary an Enabler file. To use less RAM Disk space, create and store aliases on the RAM Disk System Folder for the remaining extensions, control panels, and System Folder support files stored on the hard drive. Using the alias technique will reduce the speed benefits of the RAM Disk since the aliases refer the Finder to the hard drive to access the original files. Virtual Memory is not accessed nor used by a RAM Disk.


    Storing the RAM Disk contents:
    The Assistant ToolBox extension is supported on PowerBook computers and preserves the RAM Disk contents on supported computers. Since some desktop Macintosh computers do not support the Assistant Toolbox extension one can preserve the RAM Disk contents using other techniques.

    Once your RAM disk is completely configured, drag the RAM Disk icon over your internal hard disk icon. This creates a folder on your hard disk called "RAM Disk." This copy will serve as a backup of your RAM Disk. Periodically copy the RAM disk to the hard disk when the RAM disk changes.

    If you ever totally lose power, you can quickly restore your RAM Disk by dragging the contents of the RAM Disk folder to a new, but empty, RAM Disk after restart. Frequently back up your RAM disk to your hard disk because you may be continually optimizing it when first setting it up. It takes only a few seconds to copy the entire RAM disk to the hard disk replacing the existing folder.


    Other Tips:
    Having multiple System Folders on your hard disk is not generally recommended. Third-party utilities may prove useful including System Picker (a utility that allows you to select among different System Folders on the same hard disk).

    Another method to preserve the contents of the RAM Disk is a third-party utility called ramBunctious.


    Related articles:

    The Tech Info Library Article 16809: " RAM Disk: Description "
    The Tech Info Library Article 9334: " System 7 RAM Disk: Macintosh Computers Supported "
    The Tech Info Library Article 16810: " RAM Disk: Resizing or Deleting "
    The Tech Info Library Article 24274: " Power Macintosh G3: RAM Disk Not Saved On Restart "

Document Information
Product Area: Computers
Category: PowerBook
Sub Category: General Topics
Keywords: kpbook, supt

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