Every few months I run a selection of questions from readers. Here is the latest batch, most of which I have had to edit for length, with my responses. We will start off with a question that several people have asked me lately. Until recently, I happily edited home videos with iMovie on my G4 PowerBook 800. I downloaded iMovie 3 when it came out but, since the upgrade, iMovie crashes continually. Any suggestions? Ann Apple now has an update for fixing those surprise bugs in iMovie 3, downloadable from its Web site. But before it was released, I discovered a little-known fix for iMovie instability that also made my Mac run like a new machine. It is specifically for those using the Jaguar version of OS X. Here's the drill. Boot your Mac with the No 1 Jaguar install disk (hold down the C key while starting with the disk in the CD drive) but don't run the installer. Under the Installer Menu select Open Disk Utility. After the disk utility starts, select your start-up disk and click on the First Aid tab. At the bottom of the window there will be a Repair Disk Permissions option. When you select this you will get a more thorough permissions repair than if you just ran the Disk First Aid application in your Utility folder. After running this procedure, many of my applications became faster and more stable. I am a graphic designer and a new Mac convert and enthusiast. I so loved my first Mac's stability that last month I bought my second - an 800 megahertz eMac with Mac OS X. I installed 16 gigabytes of RAM, expected programs like Adobe Photoshop and Illustrator to run much faster, but I found only a 40 per cent increase in speed. Please tell me whether I am expecting too much or if there is anything else that can be done to get the computer to run faster? Rajesh, Shenzhen Lots of RAM will increase speed when working with large files but, if you got 40 per cent improvement, you are doing exceptionally well. Other ways to improve performance are disk optimisation (with Disk Warrior) or installing a faster hard drive. Oh, and if your budget allows, don't forget those dual processor 1.4 gigahertz power Macs. What is the difference between the new 12-inch G4 PowerBook and the 12-inch iBook? Allan Tan, Hong Kong Here is a list of differences: The G3 iBook has a 512 kilobyte online level 2 cache while the PowerBook has a 256kb L2 cache The PowerBook has PC2100 DDR (double data rate) RAM while the iBook still uses PC100 synchronous dynamic random access memory (SDRAM) The PowerBook hard drives run at the ATA/100 standard while the iBook uses the slower ATA/66 drives The iBook has an ATI Radeon 7500 Mobility graphics chipset while the PowerBook has the superior NVidia Geforce4 chipset The PowerBook has built-in Bluetooth wireless networking while the iBook does not The PowerBook can't boot into OS 9, the iBook can; The PowerBook has audio in, the iBook does not; The PowerBook is lighter at 2.09kg while the iBook is 2.22kg The PowerBook has a superior fit, feel and finish but is close to twice the cost for the base models. Yes, it's a tough decision. My PowerBook is 15 months old and after a full charge I get 80 to 100 minutes use when running on the battery. I have timed how long the battery lasts before the warning sign comes on and the battery has never lasted more than a couple of hours while I'm using Word. I'm sure that I read somewhere that it could go for up to five hours. What gives? Ashley Kim Sing, China Apple has been telling PowerBook users since January 2000 that the battery lasts five hours. The best I've ever seen in real-world use is three hours playing Solitaire. To get the most out of your battery, you need to first select the Low Energy Use settings in the Energy Saver preference pane in the System Preferences. Go to the Apple Menu?System Preferences?Energy Saver. When the window opens, set the first list to Longest Battery Life. Set the second list to Battery Power. If the second list is missing, click Show Details. From here, you can make a custom battery-saving set-up. Also, make sure that there are no CDs in the CD drive or power-hungry USB-powered peripherals plugged in. If, after doing all this, your PowerBook battery still gets under two to three hours, take it back to Apple for a checkout and possible warranty battery replacement. I study at St Paul's College and use my PowerBook G4 at home to play with AppleScript Studio. I am interested in learning how to programme to create OS X applications. Do you have any suggestions on accomplishing this? Kim Kwan, St Paul's College The easiest way to get started building OS X applications is with a program called RealBasic ( www.realbasic.com ). It contains all the parts necessary to assemble a complete application quickly. They claim that with no experience you can create an application in an hour. Also check out CodeWarrior, ( www.metrowerks.com ) a more robust and expensive OS X application development environment. Both tools make your end product usable in all popular operating systems. E-mail Dave Horrigan at email@example.com with your Mac queries.