Apple Mac OS X hints and tips

Reset the PRAM to fix Mac faults

There are different types of computer memory and the sort that you are used to is the RAM (Random Access Memory) that OS X and applications use when they are run. Programs are read into memory from the disk drive and then they can be executed. There are other types of memory though, such as PRAM.

So what is PRAM? It stands for Parameter RAM and this is NVRAM (Non-Volatile RAM - the acronyms are coming thick and fast, so keep up!).

The gigabytes of normal RAM that is used to run OS X and applications is volatile RAM, which means that when the power is switched off, it loses everything stored in it immediately. Non-volatile RAM is memory that retains its contents even when the power is switched off.

This makes it useful for storing certain bits of information that the Mac needs to remember when it is switched off. You may be wondering why the hard disk drive could not be used for this, but what happens if you plug in an external disk drive and boot from that? Or if you upgrade the drive, replace it, reformat it, and so on? The information would be lost or unavailable. NVRAM is better.

So what does the Mac store in PRAM? It depends on which Mac you have and it contains a range of information that can include any or all of the following: Display and video settings such as refresh rate, screen resolution, number of colors, startup volume choice, speaker volume, recent kernel panic information, the DVD region setting, status of AppleTalk, serial port configuration and port definition, alarm clock setting, application font, serial printer location, autokey rate, autokey delay, speaker volume, attention (beep) sound, double-click time, caret blink time (insertion point rate), mouse scaling (mouse speed), startup disk, menu blink count, monitor depth, 32-bit addressing, virtual memory, RAM disk, disk cache.

Sometimes the contents of the PRAM can become corrupted and this manifests itself as problems and errors when using your Mac. If you have a fault and you have tried everything to fix it, but have been unable to find a solution, it might just be corrupt PRAM. Resetting the PRAM can cure certain faults and it is well worth trying when everything else has failed.

To reset the Mac's PRAM, turn on the power and straight away before the grey screen appears, hold down the Command+Option+P+R keys on the keyboard. The Mac will restart and you'll hear the startup sound a second time. Then you can release the keys.

When you get back to the desktop you will need to go to System Preferences and set everything up again. It's a bit like getting a new Mac because everything is set to the defaults.

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