In your recent Firefox review, you said Internet Explorer has a private browsing mode that doesn’t record your history or tracks while surfing. But I can’t find how to turn it on.

The feature, which is called InPrivate Browsing, is only available in the latest version of IE, called IE8. You turn it on by either selecting that option from the Safety button at the upper right, or from the Tools menu in the Menu Bar if you have chosen to make that bar visible. Once you do, an “InPrivate” label appears at the top left corner of the browser and a page appears explaining that the browser won’t record on your own PC certain records of what you do in that browsing session. There’s an additional privacy mode, available from the same two drop-down menus, called “InPrivate Filtering,” which goes further. It blocks Web sites you go to from saving certain records of your presence there on their own servers. InPrivate browsing lasts until you close the InPrivate browsing window.

When you reviewed the latest Safari Web browser awhile back, you complained that Apple had repositioned the tabs in a way that made them harder to see. A friend said that’s no longer true. Is he right?

Yes. After getting a lot of negative reaction, Apple changed Safari 4’s design so the tabs are displayed in the previous manner, below the toolbar, instead of at the very top. The company also made more visible the page-loading indicator, though I personally still prefer the indicator style used in prior versions.

In your column last week, you recommended add-on software to search documents for key words in Windows XP. Is there any similar software that will do the same for Macs?

It’s unnecessary on Mac because the Mac operating system comes with a fast, comprehensive search system called Spotlight that’s built right in. Windows Vista also has a very good search system built in. The reason I recommended add-on software for Windows XP is that I consider XP’s built-in search to be slow and inferior to those in these two newer operating systems.

You can find Mossberg’s Mailbox, and my other columns, online for free at the 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.

I switched from PC to Mac a year ago, but now I am thinking of adding a Windows laptop. If I do, what kind of compatibility problem would I have? I would be using the laptop mostly to write, to send/receive email and to Web browse.

In the old days, there were compatibility problems, but most of those have gone away. Based on your simple predicted usage, I’d say that you should be fine. For instance, both Macs and PCs can interchangeably open and edit all of the major file types — JPG pictures, MP3 music, Microsoft Office documents, Adobe PDF files, etc. Email and instant messages can, of course, be exchanged between the two platforms, even if you are using different programs. And Macs understand Windows file extensions. Also, you can use both platforms simultaneously on the same home network to access the Internet.

In some cases, you might need different programs to open the same files on the two platforms. But even that obstacle has greatly diminished. For instance, programs like the Firefox and Safari Web browsers, Adobe Reader, iTunes, Microsoft Office, Google Earth, Picasa, Photoshop and many others come in native versions for both platforms that can handle the same files. And, of course, Web-based programs like Gmail and Yahoo Mail work on both. Sometimes, the same programs have different features and user interfaces on Windows and Macs, but I haven’t found these differences hard to master.

The biggest problems for average users are Quicken, whose Mac version is inferior and incompatible; Internet Explorer, which is no longer made for the Mac; and Microsoft Outlook, which is replaced on the Mac by a program called Entourage that is similar but uses a different file format. And networking can be tricky. In general, the Mac does a better job of seeing Windows PCs on a network than Windows does of seeing Macs.

I use Outlook Express for my email, and I store a lot of mail in local folders. Is there a simple way to back these up? If I buy a new computer, can they be transferred?

Yes. There are two methods. One is a manual method, which Microsoft explains in a detailed document at this Web site: support.microsoft.com/kb/270670.

The other, quicker, method is to obtain one of several utility programs that can back up your Outlook Express data and, in some cases, allow you to transfer it to another PC. I haven’t tested these in years, and thus can’t recommend one over another. But one example is a free program called Outlook Express Backup, which can be found at genie-soft.com/products/oeb. Another is a $40 program called Outlook Express Backup Wizard, which can be found at: outlook-express-backup.com.

Do you know of an iPhone GPS application that speaks directions? It would make the iPhone similar to a TomTom or Garvin GPS unit.

A: No, but Apple recently announced that, under its new 3.0 operating system for the iPhone, such programs will be possible. Several companies are believed to be working on them, and I expect them to be available later in the year. The reason none exist yet is partly legal, having to do with the licensing of the underlying maps.

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

I am a Palm Treo user and would like to get an iPhone for the apps. But I have tried the virtual keyboard on the iPhone in the store and hate it. Is there a stylus you can use for better accuracy, or some software trick?

I don’t know if they improve accuracy, but there are several stylus brands made for the iPhone and iPod Touch. They are aimed at making typing easier, especially if you have long nails or are wearing gloves. One example is the Pogo, a $15 iPhone stylus from a company called Ten One Design, at tenonedesign.com.

In addition, there are several iPhone apps that attempt to help typing accuracy by allowing you to compose emails, text messages and Twitter posts using a wide, landscape keyboard rather than the narrower standard keyboard. You type your message in these apps, and then the app sends them to the iPhone’s email program for transmission. One that I have used is called TouchType. It works with email and Twitter, and costs 99 cents.

Another interesting solution is a free app called ShapeWriter, which lets you type by sliding your finger along a keyboard to connect the letters in words. You never have to lift your finger until you are done with a whole word. Messages you compose in ShapeWriter can be saved as notes or shipped to the email program for sending.

Finally, I should note two things about typing on an iPhone. First, it’s difficult to know if you’ll be comfortable with it from just a few minutes in a store, because it usually takes a few days to master. Second, some people won’t ever find it acceptable, and these folks should choose a phone that has a physical keyboard.

In your review of the new version of the Safari Web browser, you said some Web sites were publishing methods for undoing some of the changes in it that you criticized. Can you explain how I can do that?

There are two methods for changing Safari 4 so it looks and works more like the previous versions, while retaining its faster speed. One method involves typing techie commands into the computer. But, for mainstream users, I recommend another: downloading a new free utility called Safari 4 Buddy. It’s available at swoon.net/site/software.html.

Safari 4 Buddy allows you to just check off buttons that can change the placement of tabs in Safari 4 so they’re under the toolbars, rather than at the top of the screen, and restore the blue page-loading progress bar that Apple killed. It also permits users to change other settings Apple omitted from the browser’s Preferences menus. I have tested it and it works.

However, this utility works only on the Mac version of Safari 4. I don’t know of any way to make these changes in the Windows version. Also, there’s no guarantee that Apple won’t make future modifications to the browser that might reverse any customizations Safari 4 Buddy makes.

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

I have Firefox on my home laptop, but Internet Explorer on my office laptop. Can I transfer my Firefox bookmarks on my home computer to IE on my office computer using the Foxmarks bookmark-synchronization service you recommended? And how would I go about doing it?

Yes. You start by uploading your bookmarks from Firefox at home to your Foxmarks Web account, using the Firefox version of Foxmarks. That will establish the bookmark collection on the Web site as identical to your Firefox collection. Then, you install the IE version of Foxmarks on your office computer, and, when it prompts you to sync, you can either merge the Web-based bookmarks you previously uploaded from Firefox with the ones already on IE, or choose the option to overwrite the IE bookmarks entirely with the ones online.

Does the Foxmarks service work with AOL’s browser bookmarks?

AOL’s browser is not supported. Neither are some other browsers, such as Opera or Google’s Chrome. Foxmarks currently comes in versions only for Internet Explorer, Firefox and Safari (Mac version only). The Firefox version also works with Flock, which is a browser heavily based on Firefox.

Do you have any idea what the realistic hardware requirements will be to run Windows 7?

Microsoft hasn’t announced these yet. But the requirements for the current beta version are likely to be similar to those for the final release. The beta hardware requirements are: a 1 GHz 32-bit or 64-bit processor; 1 GB of system memory; 16 GB of available disk space; support for DirectX 9 graphics with 128 MB memory available for graphics; and a DVD-R/W Drive.

In the past, Microsoft’s minimum requirements have tended to understate what’s needed to run Windows well, even when doing typical tasks. It’s too early to say if this will be true of Windows 7. But I can say that, in my testing so far, the beta of Windows 7 runs much more quickly and smoothly than Vista on the same hardware.

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

If I buy a PC with an AMD processor instead of an Intel one, will I run into any compatibility issues with common software like Vista or Office 2007?

No, as long as the AMD processor, and/or its accompanying graphics and other chips, called a “chip set,” are rated as being able to handle the graphics in the version of Vista you are buying. Each chip company makes some low-end models that handle certain tasks more slowly than their mainstream or top-of-line models. And gamers are often particular about which chip sets they buy. But, in my experience, roughly comparable AMD and Intel processors and chip sets are equally compatible with common software like Office and Windows.

I have been using the Netscape Web browser for years. I am interested in shifting to using the Firefox browser. How do I transfer my extensive list of book marks from Netscape to Firefox?

Firefox will import your Netscape bookmarks automatically during the installation process, just as it can automatically import bookmarks from other browsers like Internet Explorer, Safari and Opera.

Friends who use Macs tell me they have a removable backup device that backs up their entire hard drive, including programs. Is there something similar for PCs?

You appear to be referring to Time Capsule, which is an Apple hardware product that combines a hard disk and a wireless base station and is meant to work with the Mac’s built-in Time Machine automated backup feature. The answer is that there are many backup drives for Windows PCs, and that lots of them work with Macs as well. All the major hard-disk makers sell external hard disks that connect to a PC either directly, or over a network, and which come with relatively simple backup programs. Some of these programs will do complete, automated backups of everything on your PC, including applications. Even Apple’s Time Capsule can be used to back up files from Windows PCs, though it doesn’t come with Windows backup software, and setting it up for Windows is slightly trickier than doing so on a Mac.

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

Can you recommend a device that would allow me to surf the Web on a bedroom television connected via Ethernet and to control the device via a wireless keyboard or remote control?

Perhaps the most direct approach would be to buy the MSN TV 2 device from Microsoft that is specifically meant for browsing the Web on a TV from a distance and can be used with Ethernet. It costs $200, plus a monthly fee, comes with a wireless keyboard and remote, and can be ordered at msntv.com.

A second option would be to buy a small computer with a wireless keyboard and hook it up to the bedroom TV instead of to a computer monitor. For instance, I have surfed the Web this way using a tiny $599 Mac Mini computer from Apple, which comes with a wireless remote and accepts almost any wireless keyboard, though it doesn’t come with one. There are numerous Windows computers that could do the same, and many cost less, though most are larger.

Another method would be to use a game console capable of surfing the Web, even if you have no intention of playing games. These are made to work with TV sets, and some can use a wireless keyboard and/or wireless controller to do the job. For instance, the $250 Nintendo Wii game machine has an optional Web-browsing function.

Apple has released a Windows beta version of Safari. Is it any safer to use than Microsoft’s Internet Explorer?

It’s too early to tell, as the Windows version of Safari is still in beta and is very new, to users and hackers alike.

Certainly, operating in Windows will make Safari much more vulnerable to attack than it is on the Macintosh operating system, if only because the writers of malicious software aim their firepower overwhelmingly at Windows. While Internet Explorer is hardly impregnable, it has become safer over the years, and Microsoft certainly has much more experience battling Windows security issues than Apple does. Apple has already issued some security updates for this new version of Safari and will undoubtedly have to keep issuing more to keep ahead of the bad guys.

I am thinking of buying a ThinkPad laptop from Lenovo with AT&T BroadbandConnect. Do I still need to buy some sort of card from AT&T and insert it into the laptop, and must I pay a subscription fee to them?

No, and yes. The laptop likely has the modem for AT&T built in, so you can connect to the Internet via AT&T’s cellular network without buying an external card. However, the service isn’t free. You can’t use it without a subscription, which typically runs $60 a month.

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

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

This week, I was swamped with questions about Apple’s hot new iPhone, so this is a special all-iPhone edition of Mossberg’s Mailbox.

Can you physically remove the included AT&T SIM card from the iPhone and replace it with another AT&T card or one from another wireless carrier?

Yes, and no. The SIM card, which carries the iPhone’s account information, can be removed by inserting a paper clip into a tiny hole at the top of the phone. However, Apple says that if you replace the included card with one from another carrier, like T-Mobile in the U.S., or Orange in Europe, the phone won’t work. According to Apple, some non-iPhone AT&T cards may work, but some may not.

It’s possible that hackers will figure out a way to override this lock on other carriers’ SIM cards. But, as of now, the iPhone will work only with AT&T. Even overseas, at least until Apple does deals with foreign partners, you won’t be able to use SIM cards from other carriers. The iPhone will work overseas, but you will have to roam with AT&T and pay high charges. For instance, according to an AT&T spokesman, if you make a call in Europe, it would cost $1.29 a minute. It would cost 99 cents a minute if you are on one of AT&T’s $5.99 per month international plans.

Since the iPhone battery is sealed in and can’t be easily replaced by the user, what happens when it dies? Will you have to buy a new iPhone?

No, but you will have to send the phone to Apple, or drop it off at an Apple store, to have the battery replaced. The battery is covered during the phone’s one-year warranty period. After that, replacing the battery costs $79, plus $6.95 for shipping, and takes three business days. Details are at apple.com/support/iphone/service/battery/. Some small companies may eventually offer to do this for less, or in less time, as they have for the iPod.

One twist: because a phone is a necessity, Apple is offering loaner iPhones for $29 while your phone’s battery is being replaced, or for the period of any other repair on the iPhone. You will have to switch the AT&T SIM card from your own phone to the loaner, and then back again. Details are at apple.com/support/iphone/service/faq.

In addition, Apple warns that all the data on your iPhone will be wiped out during a battery replacement, but notes that it can easily be restored by simply syncing again with the iTunes software on your computer once you get it back with a fresh battery. That’s because, whenever you sync your iPhone with iTunes, it backs up the data on the phone. You can also use this method to fill your loaner iPhone with your own data.

Can I use the iPhone via a Bluetooth wireless connection in my car? Can I use Bluetooth to transfer files or other information between the iPhone and a computer?

In my two-week test of the iPhone, I succeeded in connecting it without much trouble to the built-in audio system and microphone on a friend’s BMW. Almost instantly, the over 700 contacts I had on my test iPhone were displayed on the car’s dashboard screen and calls could be made and received through the iPhone.

However, this first iPhone can use Bluetooth to connect only with cars and with wireless phone headsets. It cannot use Bluetooth to transfer any data to or from a computer, to play music through stereo wireless headsets, or for any other purpose. As with many other missing features, Apple has the ability to add these to the iPhone through software updates delivered by synchronizing with your computer.

If the iPhone’s Web browser is so good, why can’t it play video on Web sites I visit?

At launch, the iPhone version of the Safari browser is missing some plug-ins needed for playing common types of Web videos. The most important of these is the plug-in for Adobe’s Flash technology. Apple says it plans to add that plug-in through an early software update, which I am guessing will occur within the next couple of months. However, a separate program included on the iPhone can play a limited selection of videos from YouTube, and the phone can play videos you purchase from Apple’s iTunes store, and certain videos you create yourself.

You have been critical in the past of some smartphones that don’t allow you to delete emails with a single click. Can the iPhone do this?

Yes. If you are reading an email and want to delete it, you just tap on a trash can icon at the bottom of the screen and the message disappears into the trash can with an animation that resembles water being poured through a funnel.

However, in the iPhone email program’s list view, it takes two steps to delete an email. You have to swipe across the message header or preview with your finger, and then tap the red delete button that appears. You can also press an “Edit” button, which allows you to delete emails in the list view, but this still requires two taps per message.

Unlike on a BlackBerry or Treo, the iPhone doesn’t allow you to delete whole groups of email en masse by date, or even to select large groups and then delete them en masse. This would be a good feature for Apple to add down the line.

Can you buy an iPhone and just use it to play music and videos like an iPod, and to surf the Web or get email over Wi-Fi, without signing up for an AT&T service contract?

No. None of the iPhone’s functions, except calling 911, will work unless the phone is covered by a two-year AT&T service contract, and has been “activated” by AT&T. That will cost you $60 a month at a minimum. If you are thinking of buying an iPhone, you should plan on being an AT&T customer, and if AT&T coverage is poor where you live, work and travel frequently, I advise you NOT to buy an iPhone.

You and many others have criticized AT&T’s EDGE data network, which the iPhone uses, as slow. You have noted that AT&T has a much faster data network. Can the iPhone be upgraded to use that faster network?

No, it can’t. This first edition of the iPhone can’t use any cellular network faster than EDGE, which is much, much slower than the fastest cellphone data networks available from AT&T, Verizon or Sprint. It can, however, use very fast Wi-Fi wireless networks, when you are in range of them.

Apple hasn’t said anything about future iPhone models, but I fully expect a future model that can use these faster cellular networks, which are usually called 3G networks. So, if this is very important to you, I’d suggest waiting to see if such an iPhone emerges. But I don’t expect this to happen anytime soon.

In the past few days, AT&T seems to have tweaked its EDGE network, at least in some locations, so it runs faster than it has in the past. In my own speed tests, around Washington, D.C., I have seen repeated speeds of around 150 kilobits per second, roughly 50% better than the 100 kbps I have seen with EDGE in the past. However, I have also recorded speeds as slow as 82 kbps. And, even the new, faster speeds are way below those of the faster American cellular data networks, which can easily reach 500 to 800 kbps on a phone.

How good is the iPhone’s To-Do list or Task function?

Awful — in the sense that it doesn’t exist. The phone does have a calendar, of course, which syncs with the most popular calendar programs on Windows and Macintosh computers. And it has a Notepad, which doesn’t sync with any program on any computer (though you can email notes to yourself and others). But it has no To-Do list function at all.

Write to Walter S. Mossberg at mossberg@wsj.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 accessing financial sites on a nonsecure Internet connection, which cellphones with email capability to take abroad, and what to do about Web sites that don’t work well in Safari.

I am concerned about security on my laptop when traveling and using nonsecure Internet connections available at motels. Is there a way to be secure when accessing my financial Web sites while using a motel’s connection?

You can install a good firewall, and sweep your laptop with security software for spyware and other malicious software that might transmit passwords. And you can make sure you are using antiphishing software. Better yet, you could use a sort of private Internet tunnel, called a Virtual Private Network, or a remote control service, like GoToMyPC, so you are actually using your home PC — remotely — to contact the Web sites involved.

But, the bottom line is that, unless you are on a network that you can control and secure, such as a home or office network, I wouldn’t advise accessing financial accounts online, or performing financial transactions. I wouldn’t trust sensitive online transactions to any public Internet connection, such as those at motels. There are too many people, including other guests, the motel staff, and the people at the company that provides the motel’s Internet service, who could potentially be watching what you are doing.

Is there a cellular phone that can be taken abroad that has a good email capability, for a comfortable price?

That depends on what you’d consider “good” email capability, or what price would be “comfortable” for you. It also depends on what countries you’re heading for. But, in general, any BlackBerry or Treo that works with the AT&T (formerly Cingular) or T-Mobile networks here in the U.S. will work in Europe and in many other regions. And both have what I consider good email capabilities for the price, which can vary, depending on model, and be as low as $99.

In general we love our new MacBook laptop, but there is one thing we’re not sure how to work around. We find that there are some Web sites that don’t seem to work well with the built-in Safari browser, and on some sites, we are unable to play a video. Is there a solution?

Yes. For the Web pages that don’t work well with Safari, you can download and use as an alternative the Firefox browser, which comes in a Mac version that is essentially identical to its Windows version. You can get Firefox, which is free, at mozilla.com.

The videos that won’t play were likely produced in the latest version of Microsoft’s Windows Media format. Microsoft offers free software that allows these videos to play on a Mac. It’s called Flip4Mac and can be downloaded at: www.microsoft.com/windows/windowsmedia/player/wmcomponents.mspx.

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Because of the volume of email I receive, I can’t routinely answer individual questions by email, 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

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 the “Links” toolbar in IE 7.0, smartphones with Wi-Fi chips and information on high-definition TVs.

I know you are a big fan of tabbed browsing, but I really liked having my most frequently visited Web sites on the “Links” toolbar at the top of the browser in the previous version of Internet Explorer. Is this feature totally absent in the new IE 7.0?

Tabbed browsing and the Links bar aren’t mutually incompatible, and in fact I heavily employ both in every Web browser I use, including IE 7.0, Firefox and Safari (the Links bar is called the Bookmarks Toolbar in Firefox and the Bookmarks Bar in Safari).

To turn on the Links toolbar in IE 7.0, click on the Tools icon at the upper right, highlight “Toolbars” from the drop-down menu, and click on “Links” in the list that appears. That entry should now be designated with a check mark and the Links toolbar should appear, just as it did in the previous version.

Here’s another IE 7.0 tip. If you want to see IE’s familiar menus, which are turned off by default in the new version, click on that same Tools icon at the upper right and then click on “Menu Bar” from the drop-down menu.

Are there any smartphones like the Treo that have built-in Wi-Fi chips? I’d like to be able to use the phone’s Web browser at a Wi-Fi hot spot without using minutes. I imagine the cellphone carriers aren’t eager to offer this dual capability.

Yes, there are a few smartphones that have both the ability to access the cellphone network and the ability to use Wi-Fi wireless data networks — even though, as you note, the cellphone-network operators generally shun the idea. The latest of these is the T-Mobile Dash, which I reviewed a few weeks back. For my review, go to: ptech.wsj.com/archive/ptech-20061130.html. T-Mobile is a bit different from the other American cellphone carriers because it alone has a significant business in running commercial Wi-Fi hot spots.

Hewlett-Packard also makes a PDA that has both cellphone and Wi-Fi capabilities. It’s called the iPAQ Mobile Messenger hw6925 and is also sold by Cingular Wireless, though only to “business customers.” The new Nokia E62, sold in the U.S., doesn’t include Wi-Fi, but its nearly identical European counterpart, the E61, does, and it can be used in the U.S. by just popping in a chip, called a SIM card, from a U.S. carrier like Cingular or T-Mobile.

I’m thinking about getting a high-definition plasma or LCD television. Needless to say, I found your review helpful, but would like further information. Is there a Web site or sites you could recommend?

The Web site CNET has an excellent HDTV buyer’s guide, packed with lots of information and good explanations. It’s at: hdtv.cnet.com.

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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

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 watching Major League Baseball’s streaming Webcasts of games, the capacity of digital music players and the security of Wi-Fi.

I just bought a new Mac and I love it, but I am a die-hard Yankees fan and I find that, with the Mac, I can’t watch Major League Baseball’s streaming Webcasts of games. Is there a way around this?

Since I am a huge Red Sox fan, I hesitate to help you … but I will.

It doesn’t work, because MLB.com this year switched to a Microsoft video format that the Mac version of Windows Media Player can’t handle and it doesn’t support the Safari Web browser that Apple includes on every Mac. There is a workaround: download and use Firefox, instead of Safari; and download and install Flip4Mac, a free program that allows QuickTime to handle the newest Windows Media video format. You can get it at: http://flip4mac.com/.

But even this solution is seriously flawed. The problem — and the Flip4Mac people are working on it — is that it plays only for a few batters or so, and then you have to restart it by relaunching the TV feed in the Web site. This is a pain, but it does work, sort of.

A better solution is to simply run Windows on your Mac, and then play the MLB videos on that. I do this using a product called Parallels desktop, which runs Windows inside a window on your Mac. It’s available at: www.parallels.com.

I am not clear about capacity on digital music players. As far as I can determine, most music CDs run to about 600-700 MB, so a mere 10 CDs would fill most of a 10-gigabyte iPod, correct? On the other hand, I recently read that all of Mozart’s works would fit on a 10-GB iPod. So what’s wrong with my calculations?

When companies calculate the capacity of digital music players in terms of songs or CDs, they base their calculations on the use of music files that have been drastically shrunk from their original size on a CD. This is done by converting the songs to compressed file formats, including the MP3, WMA, or AAC formats. This is what happens when you import, or “rip,” a CD into iTunes or Windows Media Player on your computer in preparation for loading the songs onto a portable player.

A typical MP3 file compresses CD music by a factor of 10 or more. So, a 650-megabyte CD might take up just 60-65 megabytes on a computer or a portable player. There is a price to this compression: The quality of the music file is degraded. However, most people find the quality acceptable, especially with common types of music — pop, rock, country and hip-hop.

Many audiophiles and classical-music fans choose to compress their CDs less drastically, seeking a balance between space-saving and quality. This can be achieved by changing the settings in your music software. Others opt for no compression at all, though, as you noted, that severely limits how much music you can squeeze onto a portable player.

I would like to link up the computers in my home wirelessly but am apprehensive about the security aspects. Is it safe to use Wi-Fi?

Yes, in almost all cases. Wi-Fi networks come with an optional security feature that requires anyone using them to know your password. So, you can turn that on. Even if you don’t, your files would be at risk only if you had a neighbor close enough to access the network who is both skilled enough and nasty enough to want to poke around in your files. In most neighborhoods, that combination is pretty rare, as is the likelihood that hackers will drive down your street in a van with a laptop and steal your secrets.

However, I would also maintain a software firewall and turn off all file-sharing features of your operating system and other software.

There are exceptions. If you live in a large apartment building, the number of potential snoopers who are strangers goes way up, since many more people will be close enough to access your network than they would be in a suburban neighborhood of single-family homes. Also, no security system is perfect. Determined hackers could theoretically break into any wireless network.

But, in most scenarios, I believe Wi-Fi is safe.

* * *

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