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Can BootCamp mess with your Mac's PRAM?

A continuing thread in an Apple discussion board says that Windows running in the Boot Camp utility can sometimes "pervert" certain settings stored in the Intel-Mac's parameter RAM and interfere with video when rebooting into Mac OS X.
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Written by David Morgenstern on

A continuing thread in an Apple discussion board says that Windows running in the Boot Camp utility can sometimes "pervert" certain settings stored in the Intel-Mac's parameter RAM and interfere with video when rebooting into Mac OS X.

Here's the description of the problem by Coelacanth64, who said he's an educational IT consultant based in Syracuse, N.Y.:

About two months after I purchased my MBP I noticed a strange change in my display resolution at boot. The best description I can offer is that it looked "psychedelic". The colors were all distorted and almost fluid. My father's comment at the time was, "Wow, man. Far out!!" Must be a 60's thing.

Anyhow, now about every 4 or 6 boots, the problem recurs. And, the only way I can normalize things is to clear the PRAM ... Then it's fine. No matter how hard I stress the video card it's fine.

After avoiding booting into Boot Camp — without a hint of the video problem — Coelacanth64 had to use his Windows partition and thereupon found his video was scrambled.

Other readers reported that the latest Leopard 10.5.2 update didn't change this erratic behavior.

From the description, it sounds as if the CLUT, the color lookup table stored on the video card, could be scrambled when Windows closes down. Or perhaps the correct video setting in the Mac's PRAM is changed by Windows (or Boot Camp), so that Mac OS X asks for a bogus setting when the system reboots. These video settings are stored in the PRAM.

Now, several posters said they were using Core Duo-powered first-generation MacBook Pros, so that could also be a part of the problem.

Still, the fix appears to be to reset the PRAM, a longtime, almost magical, practice for solving transient issues on Macs.

Longtime Mac users refer to this resetting as "zapping." In case you're new to the Mac and have never done this before, here's the zapping process:

1. Shut down the computer. 2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4. Turn on the computer. 3. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears. 4. Hold the keys down until the computer restarts and you hear the startup sound for the second time. 5. Release the keys.

The PRAM is a small piece of non-volatile memory that stores a range of system and device settings, often accessed at boot time. For older Macs from the Classic era, this information included many networking settings. With the arrival of Mac OS X, many of the PRAM settings were moved to .plist preference settings files.

According to an Apple technical note, Mac OS X PRAM settings include:

•Display and video settings such as refresh rate, screen resolution, number of colors •Time zone setting •Startup volume choice •Speaker volume •Recent kernel panic information, if any •DVD region setting

In earlier times, the PRAM held many other settings:

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

Zapping the PRAM is one of the troubleshooting steps to take if your computer doesn't start. Apple recently released a technical note on the MacBook Air on this problem.

Unless you commit the PRAM reset steps to memory, as well as the process to reset the System Management Controller (SMC) power manager, it might be good to print out this guide before your computer doesn't turn on.

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