I have moved from a PC to the iMac. In the Windows environment, I felt a need to run utilities to clean out the registry and defragment the hard disk frequently. Is this also needed on the iMac? If so, what programs are recommended?

The Mac operating system, called OS X Leopard, doesn’t include a registry, which is a feature of Windows that holds information that programs need to operate properly. So there’s no need to clean or maintain any registry on a Mac.

Mac hard disks, like those on Microsoft (MSFT) Windows computers, can get fragmented — a condition in which parts of files are so scattered around on the disk that the disk runs slowly. However, the operating system has some under-the-covers features that generally obviate the need to run a defragmentation utility. In fact, Apple (AAPL), which calls defragmenting a disk “optimizing” it, flatly claims that “You probably won’t need to optimize at all if you use Mac OS X.” There are some Mac defragmentation utilities, but I don’t believe you will need them unless you have large numbers of extremely large files and almost no free disk space.

My son’s computer frequently gets infected with adware, pop-ups. Recently it was hit with a continuing pop-up ad called VirusHeat that touted itself as a solution to the computer’s problems. When I paid for VirusHeat, the problems went away. Is it legitimate?

According to numerous reports on the Web, including some from security companies, VirusHeat is a form of malicious or misleading software. It falls into a category that attempts to scare people into thinking their computers are badly infected, or exaggerates any problems you may have. This is a common tactic now used by creators of malware.

Some of these fake or misleading “security programs” may be designed merely to make you pay. Others may even be designed to install the very kinds of viruses, spyware or adware that they claim to fight.

I have updated to a new PC. My data are on a floppy disc. There is no floppy disc drive on this new computer. How can I transfer my data?

For around $25, you can buy an external floppy disk drive that plugs into a new PC using its standard USB port. If you do so, and connect it to the new PC, you should be able to copy your data to the new computer’s hard disk.

• You can find Mossberg’s Mailbox, and my other columns, online for free at the new All Things Digital web site, http://walt.allthingsd.com.

Here are a few questions about computers I’ve received recently from people like you, and my answers. I have edited and restated the questions a bit, for readability. This week my mailbox contained questions about recording features for newer iPods, saving files to “write protected” floppy disks and choosing the right cellphone service for your business.

If you have a question, send it to me at mossberg@wsj.com, and I may select it to be answered here in Mossberg’s Mailbox.

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I would like to record my yoga classes on an iPod for playback later, but all of the recording accessories I find work only with older iPod models. Is there a recorder that works with the new video iPods?

Yes. Next month, Belkin will begin selling a $70 plug-in recorder for the video-capable iPods. It’s called the TuneTalk Stereo, and features twin mikes, plus a jack for hooking up an external mike. I haven’t reviewed it, so can’t say how well it works. Another option is to buy an MP3 player with a built-in recorder, like Creative Technology’s Zen Vision: M.

I tried to save a letter on a floppy but received the message that the file couldn’t be saved because the floppy was “write protected.” How do I get rid of this write protection?

Floppy disks have a plastic tab that can be moved up and down to either allow data to be written to the disk, or to block the writing of data, which means the disk is “write protected.” This is intended to keep important files from being overwritten. The tab either exposes or covers a hole in the disk.

The tab is set by default to cover the hole. This allows the writing, or saving, of files. I’m guessing you moved it accidentally, so the hole is exposed, which protects the disk. To correct your problem, turn the disk over to the back, and look for the tab in the upper left. Move it to the position that covers the hole. You should now be able to save your file.

Our growing small business in Pasadena, Calif., is struggling with our decision on the right system and device for cellular phone and email. We are trying to decide between Cingular and Verizon Wireless as carriers and the Treo and the traditional model of the BlackBerry, the one with the full keyboard. What is your recommendation?

On your choice of carrier, I always suggest people decide based on coverage and reception in their home area, their office area and the areas to which they travel. Price and phone selection are important, of course, but they make little difference if you can’t get calls or email where you need them. So ask around and try and determine which one has coverage and reception where you want it.

On the devices, I generally prefer the Treo, which has a much better calendar and address book, and other features the BlackBerry lacks, including a camera, strong multimedia capabilities, the ability to edit Microsoft Office documents and a vast trove of third-party software. However, when you set up the BlackBerry server to work with the BlackBerry devices, it is a powerful email tool and an adequate phone.

One thing to note: Verizon Wireless has much faster data service than Cingular in most cities. The Treo 700s sold by Verizon Wireless use this faster service, and are more advanced than the older Treo 650 model sold by Cingular. The BlackBerry 8700c sold by Cingular is the best full-keyboard BlackBerry model, but it’s much slower than the older BlackBerry 7250 sold by Verizon Wireless, because of Verizon Wireless’s faster network.

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Because of the volume of e-mail I receive, I can’t routinely answer individual questions by e-mail, or consult on individual problems or purchasing decisions. I read all questions I receive and select three each week to answer in the column.

Write to Walter S. Mossberg at mossberg@wsj.com