[ZAPPING THE PRAM]
Contents:

What is PRAM?:

Parameter RAM (PRAM) is a private playground for Apple engineers. Some of the contents of this battery-backed memory are documented, but most remain a mysterious secret. That may be acceptable when everything works correctly, but PRAM has been implicated in various crashes and installation problems. PRAM stores various pieces of information that the Macintosh would like to remember when it is turned off or unplugged. This includes:
  • Desktop Pattern
  • Date
  • Highlight color
  • keyboard settings
  • Map settings
  • Memory settings
  • Mouse speed
  • Network settings
  • PowerBook Power Management
  • Sound settings
  • Startup disk
  • Time
  • Other undocumented and system-spefic information

Zapping the PRAM:

"Zapping PRAM" is a way of resetting PRAM back to its original factory values. The basic procedure is to hold down a special combination of keys: Command-Option-P-R while powering on the Macintosh and waiting for the start-up sound. The latest recommendation from Apple requires holding down the keys until the start-up sound has repeated three more times. (Avoid holding down the power key too long because this reportedly triggers a problem on certain Macs, in which a ROM-based debugger dialog appears unexpectedly on the screen at a later time. You can type "G" to make the processor "Go" ahead from its suspended debugging state and continue operating normally.)

After resetting PRAM, check Chooser settings and Control Panels settings, including Color, Keyboard, Mouse, General Controls, Memory, Network, Sound and Startup Disk. With PowerBooks, check the various power-management options, too.

The most thorough, and most difficult, way to reset PRAM is by removing the computer's power cord and the battery on the motherboard that powers PRAM in the absence of normal power. Pushing the power switch a few times and waiting for a half-hour or more should flush everything out, including things you may prefer to retain, such as manufacture date, the number of power-on hours, and the date and time settings. (If the battery that backs up PRAM runs low, all sorts of bizarre problems can occur on the system, and the battery must be replaced. One typical symptom is that the Mac clock changes to strange values between the Mac's zero date of Jan. 1, 1904 and the current date.)

Other Tools and Info:

A freeware utility called TechTool, from MicroMat Computer Systems, offers a much neater alternative to electrical tricks. TechTool claims to thoroughly clear all of PRAM after saving important settings to a file on disk. The utility also provides a button for rebuilding the Mac's invisible desktop files, and it lists many details about the system's operating system and hardware. TechTool 1.0.6 is available from standard freeware sources, and you can reach MicroMat at micromat@eworld.com.

Matthias Wuttke's PRAM-Reader 1.1 is also freeware. PRAM-Reader simply saves the full contents of PRAM to a disk file or restores PRAM from the file. It is useful for saving a clean copy of your settings after you go through the lengthy process of clearing PRAM and reconfiguring everything. Once you have the file, you can quickly restore from it whenever a PRAM problem is suspected. Source code is available from Wuttke at wuttke@stein.teuto.de.

A special quirk of PRAM in the Macintosh 630 models requires an additional step when zapping the PRAM. In these Macs, one is supposed to push "a red button near the SCSI connector on the logic board" whenever the logic board is removed and replaced.

When swapping NuBus cards in any Mac, it may be important to clear some data out of a special NuBus settings PRAM. Remove NuBus cards and power up the computer once before installing the new card configuration.