Let's start with a little quiz. I say, "Big, bloated, and full of errors." What do you say? Right, "Windows Registry." One more: "Messing with it is risky." If you guessed the Registry again, you pass. While fooling around with your Windows Registry does involve some risk, cleaning it out can have an impact on your PC's overall performance.

The Windows Registry is an essential system file that houses a massive collection of details about your computer -- where programs are stored, which helper programs (known as DLLs) are shared among your various applications, listings of all your Start-menu shortcuts, and pointers to the programs that fire up when you click on an icon. And that's just the beginning.

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Practically everything you do in Windows is recorded somewhere in the Registry. For instance, the URL for this article probably has an entry now. The paths to the last dozen or so images or documents you opened are there, too, as are the details of the programs you most recently installed or uninstalled.

Here's the problem: If you pry open the Registry, you'll probably find it about as cluttered as a teenager's bedroom. That's because Windows doesn't efficiently clean up after itself as it goes about its daily business. It constantly creates new entries, but seldom -- if ever -- removes them after they're no longer needed.

Compounding that problem are applications that are too inept to uninstall all of the Registry entries they create; far too often, program upgrades and installers leave unneeded pointers in the Registry. So the Registry becomes bloated with unnecessary entries, slowing down your system.

Registry Cleaners: Boon or Boondoggle?The big question is whether a Registry cleaner will speed up your PC, making it boot more quickly and run faster. The answer? I can say, emphatically and unequivocally, uh, maybe. That's right, a big, fat perhaps -- because everything depends on the condition of your Registry.

To find out which Registry cleaner catches the most errors, is the safest and easiest to use, and (just as important) creates the fewest hassles, I tested five of the most popular Registry cleaners and defraggers. Many came recommended by PC World readers. I examined two free products (Advanced Windows Care and RegSeeker) and three commercial ones (jv16 PowerTools, Registry First Aid, and RegSupreme). After all that testing, my Registry is squeaky clean -- the absolute envy of my PC World colleagues.

I tried each tool on my messy production PC using Windows XP SP3, on a pristine Fujitsu Lifebook T-Series laptop running Vista, and on an old ThinkPad laptop. I ran the Registry scan and repair module of each application, rebooted the system, and watched for problems -- and I also tried to determine whether the system seemed friskier. After each test, I restored each system to its original state of disarray with Acronis TrueImage. (Read a review of Acronis True Image Home 11 and download the demo.)

Top 10 Registry dos (and don'ts)Messing with the Registry -- and doing so incorrectly -- can destroy Windows, send your PC to computer heaven, and cause you great distress. I'm not kidding. Here are my 10 tips to keep your system here on Earth -- and to keep yourself anxiety-free.

1. The utmost protection from Registry hassles, or any computing disaster, is to have a current backup. I really mean it. As in, you ought to do one now while you're thinking about it. For a thorough tutorial, read "How to Prevent a Data Disaster" or "Fifteen Backup Programs to Safeguard Your Data." And if you don't have one, grab a backup tool from our Downloads library.

2. In most other programs that walk you through with wizards, it's no big deal if you don't pay attention and you merely keep clicking the Next button. That isn't the case with Registry cleaners. I strongly encourage you to stay alert and read whatever the cleaning tool has to say.

3. Before you open the Registry cleaner, use ERUNT (The Emergency Recovery Utility NT) to back up the Registry. Sure, I know, it's redundant, since the Registry cleaner will back up any changes it makes. But I like an extra level of security. You will, too, if something goes awry.

4. When you begin scanning, make sure not to have any applications running; if possible, it's also smart to unload any tools running in your system tray. That's because open apps are constantly making Registry changes, and you want the Registry cleaner to do its work with no interference.

5. After the scan, the program will let you remove -- or in some cases, repair -- the Registry errors. If you're given the option, set the Registry cleaner to remove errors only at the safest and least-intrusive level. (You can scan with more-aggressive settings later on.) Even at that, you might see 1,000 or even 2,000 "safe" entries that need cleaning. For instance, Registry First Aid found 2,161 problems on my production system, of which about 1,900 it deemed safe to alter.

Whatever you do, never choose an autoclean option, such as the one in RegSeeker. Ever. They are not to be trusted.

6. Choosing which of the errors to remove or repair can give you a migraine. When I inspect a list of potential entries to remove, I scan for things that look familiar. For example, in my lists I saw almost 100 Registry entries left over from a package of Dell drivers I had uninstalled months ago, and one Registry cleaner spotted invalid paths to dozens of entries for MP3 files that I had moved to a new location. Both of those catches were accurate, and gave me the sense that the program's removal suggestions were on target.

After a couple of days, if your PC doesn't do anything weird, try another scan, this time allowing the Registry cleaner to work more aggressively.

You must, however, examine entries marked with "Caution," "Extreme Caution," or some other indicator of risk very carefully. I'm still not kidding. Unless you're an advanced user and can clearly identify the scope of the entry, leave it alone. The reason is that, even if the cleaner offers an option to restore a deleted Registry entry, restoring might not be possible if the DLL entry you just deleted is essential for your system to boot.

7. Once you give the tool the go-ahead and it starts removing Registry entries, walk away from your PC. Play with the dog, have some coffee, or watch TV. This is for safety purposes: If you're fiddling with the PC -- moving the mouse, deleting desktop shortcuts, whatever -- you're making changes to the Registry while a Registry cleaner is working. Not a good idea.

8. If you discover a problem (for instance, maybe Excel no longer launches), don't panic. And don't do anything aside from using the Registry cleaner's restore feature, which ensures that only the changes the program just made are reversed. That will probably fix the problem. If not, the next step is to restore the Registry with ERUNT, the tool I mentioned in step 3. As a last resort, restore your PC with a backup program -- which you certainly have, right?

9. You needn't perform a Registry scan more than once a month or so, especially if you don't often make changes to your PC. Scanning more frequently won't hurt anything, but you're unlikely to see a significant performance boost.

10. Are you a techno-fanatic who needs the Registry to be squeaky clean, with absolutely no stray entries and trimmed of all fat? There's no harm in using multiple freebie Registry cleaners -- provided you use them one at a time. You might also want to select a Registry cleaner (such as jv16 PowerTools or Registry First Aid) that includes a defragger, or choose a free defragger such as Auslogics Registry Defrag.

Registry cleaners: How they faredIf you're like me and you constantly add and remove programs, move files around, and fiddle with I-don't-know-if-this-will-work freeware, I'm confident a Registry scrubbing will help you, if only a little bit. It did for me, though the change wasn't earth-shattering. I used a stopwatch with my desktop system, and after a cleaning I saw 10 seconds shaved off its boot time. I also noticed that Microsoft Word and an image editor loaded a little faster.

On the other hand, I didn't see a smidgen of improvement on my laptop. That's because on that machine I use the same five programs, rarely install new applications, and mostly check e-mail and browse the Internet. So scanning the Registry showed fewer than 50 problems, and cleaning didn't make any difference.

None of the cleaners managed to fix a gnarly problem I was having with spoolsv.exe. (Spoolsv.exe occasionally holds up other programs from loading on my PC.)

Your mileage, undoubtedly, will vary, and you won't know how effective a Registry cleaner is until you give it a whirl. But if nothing else, these programs will at least give you the feeling that you're taking care of your computer.

In each of the following reviews, you'll read my curmudgeonly impressions of how the Registry cleaners performed. I focused on their ease of use, the number of errors they found, and whether they introduced any hazards, such as no automatic backups.

Some of the tools I tested wanted a permanent spot in my system tray; it's not necessary, though, and when a program tried doing it, I found the option to disable the setting. And except for Registry First Aid, none of the products would repair faulty entries, but instead just deleted entries that were no longer valid.

Registry First AidRegistry First Aid is eager to help you fix and compact your Registry -- and it does a terrific job, too. Of all the programs I tried, this one inspired the most confidence, both from a safety perspective and in the way it handled Registry problems. The interface is clean and easy to navigate, and the program includes a Registry defragger, a Registry searching tool, and a built-in automatic backup module. Registry First Aid supports all versions of Windows.

The only drawback is that the program costs $28; the trial version lets you see everything the program does, and is fully diagnostic, but fixes only 14 entries at a time. I'm hoping that won't dissuade you from trying Registry First Aid.

Registry First Aid found 2,161 faulty entries in a 20-minute scan, a high number that may be explained by the program's relatively liberal definition of what constitutes a faulty entry. I was comfortable with the way it listed problems, either by category (such as invalid file or DLL, invalid path, or unused software entries) or by safety level. All of the entry issues that were safe to fix were automatically checkmarked, and I liked having to check the ones labeled "Caution" or "Extreme Caution" manually.

Most problems that Registry First Aid found were marked "Delete the entry," but some had other choices. I could cut the invalid substring or, in some cases, repair the entry. Unfortunately, the program's Help function wasn't too helpful, so I opted to use the default.

While the program was scanning, I was able to examine each listing, check or uncheck it, or open the specific entry in the Registry.

A great feature, and one worth the price of admission: With one click, most of the problem entries popped open my browser and conducted a Google search on that Registry key. Very cool, and ideal for determining whether a risky entry should be removed.

One quibble: I wasn't happy that the tool attempted to find a home in my system tray, unnecessarily adding clutter just to check for new versions. I disabled it in the settings.

RegSupremeRegSupreme, only $13, is definitely a basic, no-frills tool. It includes a Registry cleaner as well as a Registry compactor, and is essentially a scaled-down version of its bigger sibling, jv16 PowerTools (see below).

In RegSupreme you get only two levels of error detection -- safe and aggressive -- as opposed to four in jv16 PowerTools. And the program has almost no extras; the only one of value offers a way to search for specific keywords in the Registry (say, "RealPlayer"). On the other hand, the inexpensive RegSupreme has a built-in backup tool and gets the job done. So if you like jv16 PowerTools but you don't need the extra functions -- and you want to save some money -- RegSupreme could be perfect for you. Like jv16 PowerTools, RegSupreme supports every version of Windows and comes with a full-featured, 30-day trial.

RegSeekerRegSeeker is free, and alongside a Registry cleaner it has a handful of other Registry-focused utilities. The tools include a keyword finder; a utility to examine installed application Registry entries, assorted histories (for instance, Internet Explorer and Start-menu items), and Startup entries; and a tool to tweak about 24 XP settings.

This Registry cleaner is confusing because its interface sports a strangely labeled "OK!" button that doesn't really give you a sense of what the program will do next. On the same screen, the app presents a dangerous option: Auto Clean, which I encourage you to avoid. The screen provides little help or guidance, though RegSeeker warns that to back up the Registry, you must make sure to check the "Backup before deletion" option, another oddly labeled feature. The program has no automatic restore function, either; you'll need to find the saved .reg file yourself and click on it to restore your Registry.

On my production PC, RegSeeker picked up 1108 problems. Unfortunately, the program offered no assistance in determining which of the errors needed deleting; it also didn't provide categories, such as invalid path or shared DLL, in order to help me decide whether items were safe to delete. RegSeeker isn't for novices. It supports Windows 2000, XP, and Vista.

Advanced WindowsCare PersonalAdvanced WindowsCare is a freebie and comes with other tools besides a Registry cleaner. For instance, it claims to deter and remove spyware, optimize your PC, manage your Startup items, and remove junk files. I focused only on the tool's Registry skills, and didn't try any of those other components.

Though Advanced WindowsCare found 323 Registry issues, about the same number as jv16 PowerTools picked up, its presentation of the scanning results was pitiful. Unlike other tools that supplied detailed information about each problem, a choice of fixes, or a way to open the Registry to see the actual entry, Advanced WindowsCare just showed me a list. The program uses a minimalist approach: Each item sports a cautionary orange or red symbol (with no legend), the Registry key location and value, and an error description (obsolete software key or missing MUI reference, for instance). And rather than providing a built-in backup module, Advanced WindowsCare simply offered a menu item that brought me to Windows System Restore.

One more issue: You'll need to pay attention when you install Advanced WindowsCare's free scanner -- unless you clear the check boxes, the fool thing will automatically add the Yahoo Toolbar to your system and make Yahoo your Web browser's home page. Not good.

The program supports Windows 2000, XP, and Vista, but I'd recommend it only to advanced users.

jv16 PowerToolsFor $30, you can pick up a copy of jv16 PowerTools (a more-complete sibling to the streamlined RegSupreme). In addition to a Registry cleaner and compactor, it has other tools that will tell you all you ever wanted to know about the Registry -- but you probably wouldn't use most of them. Among the tools are utilities to manage the Registry, find and replace entries, monitor Registry changes, take a snapshot, and get Registry stats. The collection contains other modules, too, including file finders and cleaners, duplicate finders, and an assortment of system management tools, such as a startup manager and a history cleaner. jv16 PowerTools supports every version of Windows and comes with a full-featured, 30-day trial.

In its aggressive mode, the Registry cleaner in jv16 PowerTools found 392 Registry problems; in its normal mode, it detected 298 problems. The program gave me two ways to fix the problems. The first option was to back up the Registry and let jv16 make all the changes it wanted to -- a choice I wasn't happy with and wouldn't use. On the other hand, when I chose the "Custom fix" alternative, the program forced me to look at each problem one at a time. Other apps, such as Registry First Aid, list all the items and let you select specific entries by checking the boxes beside them, which is much easier. I also wished that the program showed the severity of each problem so that I'd know which ones were important, but it didn't.

jv16 PowerTools' Registry Cleaner component includes a slider bar for you to decide how aggressively you want the tool to scan -- safe, normal, aggressive, or very aggressive. After the scan, a report shows a graph with the number of errors, from high to low. The feature is interesting but not terribly valuable, since it doesn't offer any details about how it's identifying the problems.

A nice touch, however, is that the opening series of screens provides helpful tips to use the program -- I recommend you read them thoroughly.

One final note: Keeping your system free of unwanted applications with a good uninstaller utility will help eliminate the need for a dedicated Registry cleaner. For a program that's proficient at removing applications, read "Revo: The King of Uninstallers"; you can download Revo from our library.

PC World is an InfoWorld affiliate.

Microsoft this week is proceeding with an update to Windows Vista and Windows Server, making available a beta-level service pack featuring capabilities for virtualization and power savings.

The company on Tuesday began offering the Windows Vista and Windows Server 2008 SP2 (Service Pack 2) Beta release to MSDN and TechNet subscribers and will extend it to the public via TechNet on Thursday. Offering a single service pack minimizes deployment and testing complexity, Microsoft said.

Included in the service pack, according to the Windows Server Division blog, are Hyper-V bits in the release-to-manufacturing stage, meaning the bits are completed. Hyper-V is Microsoft's hypervisor-based server virtualization technology enabling multiple operating systems to run on a single physical machine. This enables workload consolidation across multiple underutilized servers onto a smaller number of machines.

Also highlighted in the service pack are changes to the power profile to yield more power savings. The service pack also addresses reliability and performance issues and supports new types of hardware. The 64-bit CPU from Via Technologies is supported and performance is improved for Wi-Fi connections after resuming from sleep mode.

"We are tracking to ship SP2 in the first half of 2009," said Justin Graham, senior product manager for Windows Server, in the blog.

With the release, Microsoft is looking for developers and IT professionals to have an early look at the technology and offer feedback. The beta is being offered via a Microsoft Customer Preview Program (CPP)

"The CPP is intended for technology enthusiasts, developers, and IT pros who would like to test Service Pack 2 in their environments and with their applications prior to final release. For most customers, our best advice would be to wait until the final release prior to installing this service pack," said Mike Nash, corporate vice president for Windows Product Management at Microsoft, in The Windows Blog on Tuesday.

"Windows Vista SP2 builds on the solid foundation of Windows Vista SP1, and represents our ongoing commitment to Windows Vista today," Nash said.

VMware released on Tuesday VMware View 3, new software aimed at providing desktop virtualization, application virtualization, and management of virtual desktops in one product.

VMware View is a reworking of the company's VMware Desktop Infrastructure product that adds other components to solve the problem of managing virtualized desktop environments, said Raj Mallempati, a group product manager of desktop products for VMware.

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VMware View is part of an initiative that VMware is calling vClient, which it unveiled at its VMworld conference in September. Mallempati said with the vClient strategy, VMware hopes to solve the "desktop dilemma" of not only virtualizing applications and desktops, but also managing and deploying those environments.

"At the end of the day, we also want to make sure we can provide end-users with a virtualized view of their desktops, applications and data," he said.

In addition to providing desktop virtualization, VMware View 3 includes View Composer, a new product that creates virtual desktops from a master image; VMware ThinApp, which simplifies application packaging and deployment to a virtual desktop environment; and Offline Desktop, which provides the ability to move virtual desktops between the datacenter and a local laptop or desktop. The product also includes Unified Access, which provides desktop administrators a single management platform for virtual desktops and applications.

VMware View 3 comes in an Enterprise Edition and a Premier Edition. The Enterprise Edition includes VMware Infrastructure Enterprise Edition, VMware View Manager 3, and Unified Access, and it costs $150 per concurrent user for a perpetual user license. The Premier Edition includes those products but adds VMware View Manager 3, VMware ThinApp, VMware View Composer, and Offline Desktop. It costs $250 per concurrent user for a perpetual license.

As virtualization of server OSes becomes more common, both VMware, which remains the leader in the virtualization software market, and other vendors are expanding their offerings to tackle the problem of virtualization desktops and applications that run on desktop computers.

Even though VMware remains the leader in virtualization across the board, the company has had a bumpy year in which it's faced its stiffest competition to date. Vendors such as Microsoft are building virtualization directly into their server OSes and are branching out into desktop and application virtualization. And in July, the company had a major executive shake-up, with CEO Diane Greene leaving suddenly to be replaced by former Microsoft executive Paul Maritz.

Oracle has contributed data-integrity protection code, partly developed with the hardware vendor Emulex, to the Linux kernel, the vendors announced Tuesday.

The code helps maintain "comprehensive data integrity" as information "moves from application to database, and from [the] Linux operating system to disk storage," according to a statement. It also lowers the possibility that erroneous data will get written to disk.

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The companies' effort is meant to help datacenter administrators track and address corrupted data quickly, lowering costs and downtime, said Scott McIntyre, vice president of product marketing at Emulex, in a statement.

Oracle and Emulex, which makes products for connecting servers, networks, and storage systems, are developing an early-adopter program that will help customers start working with the new features.

When a lot of information is moving through various aspects of a system very quickly, its integrity can suffer, said Redmonk analyst Stephen O'Grady. And at the same time, data integrity grows more vital as systems scale up, he added.

But improvements like the code contribution announced Tuesday are only "one piece of the puzzle," and will work in tandem with next-generation Linux file systems now under development, such as Btrfs, he said.

The Btrfs project, now available under the GPL open-source license, was first developed at Oracle.

Oracle is a key contributor, along with other large vendors, to the kernel project. The company makes money on Linux through its Unbreakable Linux support service.

Microsoft has released a new wave of Windows Live services that adds more social-networking qualities to its set of online services.

The company unveiled last month a plan to add Facebook-like qualities to its set of online services, which include e-mail, calendaring, instant-messaging, photo-storage, and sharing and collaboration services, among others. At the time, the company said the new services would be available to users before the end of the year.

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Microsoft first revealed the Windows Live brand for its online services and a plan for a major overhaul and to add new services in November 2005. The services are aimed at competing with Google by making Windows Live Web users' entry point into the Web and ultimately allow Microsoft to sell more online advertising.

The new version of Windows Live services lets people users have designated as "friends" see activities they are doing in other Web applications through Windows Live Hotmail, Windows Live Messenger, and other Live applications and services. The capabilities will be similar to the way Facebook allows users to be notified via e-mail or on its Web site about what their friends have been doing in the applications they use on Facebook, a feature called the "news feed."

To provide the new "activities" feature, Microsoft has partnered with popular third-party Web sites to link their applications with Windows Live, including Flickr, iLike, LinkedIn, Yelp, Flixster, Pandora, Twitter, Photobucket, and Tripit.

In addition to updates to existing services, such as Windows Live Messenger and Windows Live Spaces, there also are several new services available to users with Tuesday's release.

They include Windows Live Groups, a service for letting teams, clubs or other groups of people collaborate and engage in online discussions; Windows Live Photos, a new photo-storage and sharing service; Windows Live Profile, a way for people to share information about themselves with more than 50 partner sites; and Windows Live People, which allows users to store and manage Windows Live contacts.

Users can access the new services online now.

Zoho, maker of an on-demand suite of business and productivity applications, announced on Tuesday CloudSQL, a new service that lets developers use the ubiquitous SQL to connect Zoho data with other cloud-based or on-premises applications.

SQL is a "pretty old" language but is also "pretty awesome," said Zoho's director of marketing, Rodrigo Vaca, in a blog post Tuesday. "It is by far one of the easiest and most efficient ways to query and interact with structured data. That's why it remains by far one of the most heavily used languages for business applications."

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Cloud computing has ushered in new methods of data retrieval and storage, leading to "improved, faster, and more responsive Web applications," Vaca added. "But while there are some SQL-like approaches for cloud computing out there, they tend to be fairly limited and not as powerful as the full-blown SQL."

CloudSQL supports a wide range of SQL variants, including ANSI, Oracle, Microsoft SQL Server, IBM DB2, and MySQL.

The service "serves as the bridge between the external application and the data stored inside Zoho. It receives the query in SQL, interprets it, delegates queries and aggregates results across the Zoho services," Vaca wrote.

The company has also developed a JDBC (Java Database Connectivity) driver and is working on an ODBC (Open Database Connectivity) driver. This means developers "can just continue using SQL drivers and statements as they already regularly interact with their premises-based databases using JDBC or ODBC drivers," Zoho said in a statement.

Initially, Zoho Reports, a BI and reporting service, will support CloudSQL. Other products, such as Zoho CRM, will support it down the road.

Zoho's announcement represents an attempt to win over IT specialists who haven't been quite ready to embrace the cloud-computing model, one observer suggested Tuesday.

"CloudSQL simply represents an incremental move that will enable Zoho to grow, extending a comfort blanket to nervous DBAs seeking reasons to resist relinquishing control over their data," wrote Paul Miller, a blogger who tracks trends in cloud computing and the semantic Web.

For now, CloudSQL is available at no cost. Zoho, which is a division of the Pleasanton, Calif., company AdventNet, will monitor usage and decide whether it needs to begin charging for it, according to a representative.

CloudSQL is somewhat unusual in that it lets users connect their Zoho apps and others in a free and broadly compatible manner, instead of forcing them to use a proprietary tool that carries a price tag, said RedMonk analyst Michael Coté.

"Access to data is the key problem for all these [cloud-based applications]," he said. "That's where the lock-in is, it seems, in such offerings. Whoever controls access to the data can control pricing."