RAM, or "Parameter RAM," is a section of memory used to store some system and application settings that are more "vital" or "universal" than those kept in the Preferences folder of your System Folder. Most user settings that must be retained after the computer has been turned off, and that need to be present at system startup, are stored in PRAM. The PRAM itself is 256 bytes of data stored in your Mac's real-time clock chip, along with the date and time settings. This insures that no matter what system version you start up with, or what different system software (extensions, control panels, etc.) you use, certain settings remain the same from one startup to another.
PRAM can be broken down into several types/parts:
1) Low PRAM: the part commonly known as "PRAM," this is where most system software and applications store their settings.
2) High PRAM: the "deeper" part which is not automatically reset through a standard PRAM reset (below). This part of PRAM includes data such as the date of manufacture of your computer, hours of use, factory service settings, etc. Apple recommends that software developers do not use this part of PRAM for settings, but some still do.
3) Non-volatile RAM (see "PCI Macs" below): stores such information as the display settings on a PCI Mac. One of the design engineers at Apple has explained that "NVRAM is actually a separate 8Kx8 battery powered SRAM..."
While the settings in PRAM rarely get corrupted (damaged), it does occasionally happen, and when your PRAM settings become corrupted, strange things can happen... A common (some say too common) procedure used to solve pesky problems is to "zap" your Mac's PRAM, either manually (see instructions below) or using a utility like MicroMat's free TechTool. A standard "zap" (see "NuBus Macs" below) resets only the "low" PRAM. A zap of NVRAM (see "PCI Macs" below) resets both the low PRAM and the NVRAM. Finally, using a utility like TechTool resets all of the PRAM. Note that this includes your computer's date of manufacture and hours of use; fortunately, TechTool restores this data after the computer is restarted.
HOW TO "ZAP" IT:
NuBus Macs:
If you have a non-PCI Mac, you "erase" the PRAM by holding down the Command- Option- P- R keys simultaneously at startup. This resets the machine to its default configuration settings.
Zapping the PRAM forces the display to startup in its default configuration, all the way through the startup process. On a NuBus-based Mac, the Display Manager recognizes that the PRAM has been cleared and does not try to restore the display to its previous resolution.
PCI Macs:
On a PCI Mac, while most settings are stored in PRAM, just as with the NuBus Macs, the display information is not kept in PRAM, but is instead stored in what is called Non-volatile RAM (NVRAM). This is an important distinction because NVRAM is not cleared by using the above procedure during a warm or soft restart (by selecting Restart from the Special menu, or by using the control- command- power key combination), whereas PRAM is cleared in that case. To clear the NVRAM, you must hold down the Command-Option-P-R keys simultaneously as soon as possible after hitting the power-on key (from a cold startup). The clearing of NVRAM happens BEFORE you see the gray screen on startup. Once the gray screen appears, the PRAM is cleared at the same point as it is on NuBus machines.
To complete the process of resetting the display information back to its default configuration, you must follow these steps:
• Zap the PRAM from a cold startup (above).
• After you hear the "startup" sound twice, release all four keys and press the Shift key to start up with extensions off.
• Go to the "Preferences" folder inside the System Folder and find the "Display Preferences." Move this file to the trash, empty the trash, and restart the computer.
NOTE: There are actually two other ways to reset the PRAM, both of which are only suggested for emergencies and to be done by those very comfortable taking their machine apart. The first is to remove the Lithium battery on the motherboard for 10 minutes or more (30 recommended). The other is to press the small red or black button that is found on the motherboard on some Macs. Both of these steps will clear all of the PRAM and NVRAM.
WHAT "ZAPPING" IT RESETS:
Zapping your PRAM resets some common control panel settings to their default value, so you'll have to go back and change them to your preferred settings. The following is a short list of what gets reset when you do a standard PRAM reset, and their default settings, if available:
• "Memory" control panel:
o 32-bit addressing: early Macs, "off"; later Macs (Quadra, etc.), "on"
o Modern Memory Manager "on"
o Virtual Memory "off"
o RAM Disk "off"
o Disk Cache:
• Under 7.5.2 and earlier, 16K for every MB of physical RAM installed
• Under 7.5.3, 32K for every MB of physical RAM installed
o NOTE: the cache settings above are according to Apple; however, some people
seem to always default to 96k
• "General Controls" control panel:
o Insertion Point Blinking to middle setting
o Menu Blinking to "3"
o Both "Folder Protection" settings "off"
o Documents setting to "Last folder used in the application"
o Desktop setting to "Show Desktop when in background"
• "Date & Time" control panel:
o"Time Zone"
o Display format and alarm reset
• "Highlight color" and "Window color" in the "Color" control panel to "black"
• "Keyboard" control panel:
o Key Repeat Rate to fourth setting from the left.
o Delay Until Repeat to 2nd longest
o Layout to U.S.
• "Mouse" control panel/"TrackPad" control panel:
o Mouse Tracking/Drag Speed to third setting from left
o Double-Click Speed to middle setting
• "Monitor" or "Monitors & Sound" control panel:
o Primary monitor only
o Location of extra set to B&W monitors
• QuickTime Settings: both to "on"
• Brightness in the "Screen" control panel
• Power Macintosh Upgrade Card is reset to "Off"
• System Beep in the "Sound" or "Monitors & Sound" control panel to "Simple Beep"
• On some Macs, AppleTalk is turned off
• Under Classic Networking, the"Network" control panel is reset to "LocalTalk"; the AppleTalk port is set to the printer port. Under Open Transport, these are reset to whatever the settings are in the AppleTalk configuration file
• Startup Disk set to none (uses default of primary drive, or searches SCSI chain if not found)
• On 68040 Macs, "Cache Switch" control panel set to "Faster"
• SuperMac video cards lose their settings and need to be reconfigured
• You may need to re-select your printer in the Chooser
•The following settings are also reset on various PowerBooks:
o Minutes Before System Sleep (8 Minutes)
o Minutes Before Hard Disk Sleep (4 minutes )
o Macintosh PowerBook Rest (default is Rest)
o Stay awake when plugged in (default is unselected)
o Modem Selection
o Wake on Ring unselected
o Power Saver on the PowerBook 170 (default is Off).
o SCSI Disk Mode in the PowerBook Setup control panel to "2"
Except for the date and time and the default application font, all of these preferences, and any other system-wide settings, may be reset by zapping PRAM
A SIDE NOTE ON FINDER PREFERENCES:
The Finder Preferences file, found in the "Preferences" folder inside your System Folder, contains some settings which are commonly mistaken as residing in PRAM. These settings actually get corrupted far more frequently than those in PRAM. A common troubleshooting procedure is to "trash" your Finder Preferences to get rid of problems associated with these corrupt settings. Trashing the Finder Preferences file returns the following settings to their defaults:
• "View" control panel:
o Font for views to "Geneva 9"
o Icon Views to "Straight grid"
o Icon views "Always snap to grid" de-selected
o List View to smallest icon
o Sizes, kinds, labels, and dates selected; version, comments de-selected
o Calculate folder sizes and Show disk info in header de-selected
• "Warn before emptying" setting for the Trash Can "on"
• Trash Can moved back to default position
• Clipboard windows moved back to default position
ANOTHER SIDE NOTE ON BATTERIES AND PRAM:
Every Mac has a battery on its logic board which is used to maintain the PRAM when the computer is turned off. After a few years, this battery will run down and need to be replaced. If this happens, all of the PRAM settings above will be reset to their defaults each time the machine is shut down. The effect of having a dead battery is thus the same as "zapping" the PRAM at every startup. If you notice that some settings seem to be reset regularly (one of the most common ones is that users on an Ethernet network are always being reset to LocalTalk at startup), you should check your battery for replacement (or take your Mac to your local dealer if you're uncomfortable with taking your computer apart yourself).
A FINAL SIDE NOTE ON SOME OTHER SETTINGS:
The Virtual Memory, File Sharing, and Window Color settings are stored within their respective control panels and cannot be reset using these methods. Virtual Memory and File Sharing can be temporarily disabled, however, by pressing the Shift Key while starting the Macintosh to start with extensions off.
