The Visual Basic 6.0 product line is now more than a decade old, and the majority of Visual Basic 6.0 customers and developers have adopted the .NET Framework and are in the process of, or have already completed, the migration of their key Visual Basic 6.0 assets. Still, many companies retain a valuable portfolio of stable, legacy Visual Basic 6.0 applications that they would like to continue to support in Visual Basic, either for a year or two while other applications are migrated, or for many years.

This article will provide guidance for companies that want to keep some of their Visual Basic 6.0 assets operational and available indefinitely, while simultaneously mitigating the risks that are inherent in running legacy technologies in a modern environment.

There are four main technological choices for virtualization:

1. Virtual PC, where the virtual computer is hosted on an end-user’s machine. While this requires extra end-user training and high-end computing resources on the client, it keeps IT support to a minimum and comes closest to replicating the original application environment without additional expenditures
   
2. Virtual Server with Terminal Services, where the virtual computer is hosted on a server and delivered to end-users via terminal services. This works better in an environment where end-user computing resources are limited and there are a large number of users.
   
3. Application Virtualization, where the application layer itself is virtualized, not the entire operating system. This approach works best when a widely-used application is incompatible with modern software, but where extensive application use of local computing resources like the registry, local temporary files, etc. makes Virtual Server with Terminal Services impractical.
   
4. Finally, if the application has no compatibility issues and is easy to support, simply leave it as is.
   

There are many reasons an organization may choose to use virtualization technologies, but in the context of Visual Basic 6, there are five main areas an organization should consider:

1. Is the application incompatible with modern software that must be in place on end-user machines?
   
2. How many application end users are there?
   
3. What are the costs of supporting the existing, unvirtualized application on end-user desktops?
   
4. Does the application have personalization, registry, local file access, or other features that make it impossible for each end-user to run the application on a single machine?
   
5. What kind of computers do end users have? Can they support a Virtual PC?
   

These five factors, while not an exhaustive list, should help organization determine how to assess which virtualization technologies are the best fit for their environment. The following table gives a summary of how these five different factors relate to virtualization options.

Application Factor	Leave in place	Virtual PC on Client	Terminal Services & Server Virtualization	Application Virtualization
Application incompatibility with modern software	No	Yes	Yes	Yes
Number of end-users	n/a	Few	Many	Many
Support/Deployment Costs	Low	Moderate	High	High
Application has personalization or local-state requirements	Yes	Yes	No	Yes
Users have high-powered, modern computers	n/a	Yes	No	n/a

Beginning from the assumption that the preservation of legacy applications is (and always has been) a completely normal and typical responsibility of IT organizations, this article will walk through concrete tactics that can be used to preserve the Visual Basic 6.0 application investment of a company, while mitigating the risks of keeping older software running. For the purposes of illustration, this article will consider a number of "typical" application types, and focus on how to preserve and keep them available.

Application #1: Stand-Alone Desktop Application

Application #2: Client-Server Application

Application #3: Three-Tier Application

If, for whatever reason, a legacy application is not compatible with a new OS (for example, Windows Vista or Windows Server 2008), you can create a virtual machine, install a compatible OS in the virtual machine, and then install the legacy application. This allows the application to run in an isolated and completely compatible environment, even as your IT organization upgrades to the latest hardware and rolls forward to the latest operating systems. Hardware virtualization is the easiest and most certain way to preserve legacy applications and make them available.

Microsoft provides three hardware-virtualization products:

• Virtual PC 2007
  
• Virtual Server 2005 R2
  
• Windows Server Virtualization (currently, in beta and code-named "Hyper-V")
  

Virtual PC allows you to run virtual machines on your local desktop. Specifically designed to support older desktop operating systems on newer operating systems and hardware, Virtual PC 2007 is available for Windows XP and Windows Vista host operating systems. It offers performance improvements, such as support for 64-bit virtualization hosts and for first-generation virtualization enhancements that are built into the newer AMD and Intel processors.

Figure 5. Legacy application running locally on a virtual machine

Figure 5 illustrates how Virtual PC 2007 can keep available a legacy application that depends on Windows XP and Office XP, in an environment in which Windows Vista and Office 2007 are the corporate standard. When the user wants to use the legacy application, they first start a Windows XP virtual machine, and then they run the application within the virtual machine. If the legacy application requires an earlier version of Microsoft Office, this earlier version also runs inside of the virtual machine, and is isolated from the daily productivity suite of the user.

Virtual PC 2007 provides good integration between the host and guest OS. For example, you can perform copy-and-paste operations between the host and guest computers. You can also drag files from the host computer and drop them into the guest computer. Shared Folders also provide an easy mechanism for moving data into and out of the virtual machine.

Virtual PC 2007 focuses on desktop operating systems, including Windows 98, Windows ME, Windows 2000 Professional, Windows XP Home Edition, Windows XP Professional, Windows Vista Enterprise, Windows Vista Enterprise Business, and Windows Vista Enterprise Ultimate.

Virtual PC 2007 is available free of charge. It can be downloaded from https://www.microsoft.com/downloads/details.aspx?FamilyId=04D26402-3199-48A3-AFA2-2DC0B40A73B6&displaylang=en.

Where Virtual PC allows you to run virtual machines on your local desktop, Virtual Server allows you to run virtual machines on server-class hardware. Virtual Server 2005 R2 Service Pack 1 is the Microsoft flagship product for server virtualization. It is available for the Windows 2000, Windows Server 2003, and Windows Server 2008 host operating systems, and is designed with scalability in mind. It supports both 32-bit and 64-bit hosts, and 32-bit guest operating systems. On 64-bit hosts, it can scale up to 512 virtual machines—addressing up to 256 GB of memory. It also supports virtualization enhancements that are included in AMD and Intel processors, which further improves performance.

Typically, Virtual Server is the best choice for preserving legacy-application investment. If you have legacy applications that require a certain OS, you can configure a server with Windows Server 2003 R2 and Virtual Server 2005 R2. On that server, you then create a virtual machine that has the required OS.

For example, if your Visual Basic 6.0 application requires Windows 2000 Workstation, or even Windows NT 4.0, you could create a virtual machine with that OS, and then install your application on that virtual machine. Users could make a remote-desktop connection to the virtual machine and run the application, as shown in Figure 6.

Figure 6. Accessing an application that is running on a remote virtual machine

Each virtual machine can have up to 3.6 GB of RAM and up to four network interfaces. Virtual Server 2005 R2 SP1 ensures that virtual workloads do not affect each other (or affect the host OS), as Virtual Server allows you to throttle the amount of CPU that is used by any given virtual machine.

Virtual Server 2005 R2 SP1 also features Undo and Differencing Disks, which let you back-out changes that are made to the virtual machine.

Last, but not least, Virtual Server 2005 R2 SP1 can apply existing security models to every virtual machine, thanks to its tight integration with Microsoft Active Directory.

Microsoft offers Virtual Server 2005 R2 SP1 free of charge. It can be downloaded from http://www.microsoft.com/technet/virtualserver/software/default.mspx.

Windows Server 2008 will bring a new form of hardware virtualization to the Microsoft product line. Unlike Virtual Server 2005, "Hyper-V" is a bare-metal VMM that will provide better performance and scalability. Thanks to a new virtualized I/O architecture, pass-through access to storage devices, and support for the latest virtualization features that are included in AMD and Intel processors, "Hyper-V" will reduce the typical virtualization overhead and offer substantially better performance.

At the same time, "Hyper-V" will become the solution of choice for running the most complex and resource-intensive applications. "Hyper-V" will support 64-bit guest operating systems and virtual symmetric multiprocessing (vSMP), and will allow you to allocate more memory to virtual machines than Virtual Server 2005 and Virtual PC 2007 allowed.

"Hyper-V" will further extend the Undo and Differencing Disks concept that was introduced in Virtual Server 2005—allowing you to taking snapshots of running virtual machines, and quickly revert to those snapshot points.

"Hyper-V" will be tightly integrated with Microsoft Active Directory, to allow granular assignment of virtual machines to specific domain groups and users.

Microsoft will offer "Hyper-V" as an integrated component in every Windows Server 2008 installation, and will allow a smooth transition for its customers who currently are implementing Virtual Server 2005 R2 SP1.

Like Virtual Server, "Hyper-V" focuses on server OS support, including the Windows 2000, Windows Server 2003, and Windows Server 2008 families. It is slated to ship as beta technology in Windows Server 2008 and to be finalized within 180 days of the release of Windows Server 2008.

The first application example is a stand-alone desktop application that processes information that is exported from a mainframe, and generates reports. The application is specified as follows:

• Processes text files that are exported from a mainframe, and generates monthly reports.
  
• Must be installed on the computers of three users: one person who has the primary responsibility of generating the reports, a backup resource who can generate the report when the primary individual is unavailable, and their manager.
  

The application is not compatible with Windows Vista, because it reads from and writes to files that are under C:\ and other directories that are protected in Windows Vista. There are too many hardcoded file paths to fix easily, and the security policy of the company requires users to run UAC and log on as non-administrative users.

The decision process for preserving this specific application might be as follows:

1. The users are running Windows Vista, and the application is not compatible with Windows Vista. This leaves only two options:
   
   1. Run the application as virtualized on the local computer.
      
   2. Run the application remotely.
      
2. Running the application remotely requires configuring a server with the application installed, and providing access to that server for the users.
   
3. There are only three users who need access to this application, and they are all within the same department.
   
4. The application is relatively lightweight, and does not require extensive amounts of disk space or memory. In addition, the application does not connect to a back-end database. It needs only text files as input.
   
5. The users have newer computers, with 2 GB of memory and 80 GB of disk space.
   
6. For the IT department to configure a server for this application will take weeks or months, given current high-priority IT projects that are in progress.
   
7. Virtual PC 2007 is compatible with Windows Vista. Users could use Virtual PC 2007 to run the application in a Windows XP virtual machine, on their local desktops.
   
8. Running the applications in a local virtual machine would let users drag files that are exported from the mainframe and drop them into the virtual machine for processing by the application. Alternatively, the application that is running in the virtual machine could connect directly to a share that contains the files that are to be processed.
   
9. If running the application in a local virtual machine is difficult to support or otherwise problematic, the virtual machine could be moved easily to a central server later.
   

Based on this analysis, it makes the most sense to use Virtual PC 2007 to run a Windows XP virtual machine on the local computer of the user.

Figure 11. Stand-alone application running on a virtual machine

This will provide access quickly to the legacy application before the reports of next month must be generated, and will minimize the impact on a busy IT organization. If the solution continues to work well, it can be left in place as is. However, if the IT organization does not want to put one-off solutions such as this one in place frequently, the virtual machines can be moved later to a server that is in the data center, where they can be centrally backed up and managed. The only change to users is that they would access the virtual machines through a remote desktop connection, instead of launching them locally by using Virtual PC 2007.

The second application example was a client-server application that is used by the sales team. The application is specified as follows:

• The client UI is installed on the computer of each sales representative, and there are 30 sales representatives. It is rare for more than five people to use the application concurrently.
  
• The application does not maintain any state—such as registry keys, local files, and so forth—on the host computer. In other words, the application could have multiple instances running on the same computer without a problem.
  
• While the client application itself is compatible with Windows Vista, there are many critical forms that use a complex, third-party ActiveX control that does not run on Windows Vista. The company that built the control no longer is in business, and the control is used so frequently in the application that it is not feasible to remove it.
  
• Each client connects to a back-end SQL Server 7.0 database (SQL Server 7.0 is not supported on any OS after Windows Server 2000). While the company could upgrade to a more recent version of SQL Server, it has decided not to, for the time being.
  

Obviously, this application is more complex than the stand-alone application; however, by analyzing each piece—client and server—independently, the best solution for preserving the application can be obtained.

The virtualization solution here is to virtualize both the client and the server applications, and have them run on a server. Users would connect to the client application by using either Windows 2003 Terminal Services or the Windows 2008 Seamless Windows terminal-server technology.

1. The back-end database is SQL Server 7.0.
   
   1. SQL Server 7.0 is not supported on any OS after Windows Server 2000.
      
   2. Windows Server 2000 can be run as a virtual machine by using Virtual Server on Windows Server 2003 or Windows Server 2008.
      
   3. Running the database as virtualized allows the database server to be consolidated on the latest hardware with other servers.
      
2. The client application is not compatible with Windows Vista, and some of the users are running Windows Vista. This leaves two options:
   
   1. Run the application as virtualized on the local computer.
      
   2. Run the application remotely.
      
3. The application is needed by 30 users. Having 30 users run local virtual machines is prohibitive for the following reasons:
   
   1. Doing so requires each user to have 2 GB of physical memory, and approximately 10 GB of free disk space. Ensuring this across 30 users might be difficult.
      
   2. Having each user run the virtual machine locally complicates the configuration of the computer of the user, each of which would need more than the standard IT configuration.
      
   3. Training new salespeople (who are the users of this application) is more complicated, because they need to understand the basics of Virtual PC 2007.
      
4. The application could be run remotely.
   
   1. The application is compatible with Windows Server 2003.
      
   2. By using Terminal Server, multiple users can connect to the Windows Server 2003 computer on which the application is installed and run the application simultaneously; however:
      
   • The application was designed to be run on a workstation, and it does not work correctly if multiple users try to run it simultaneously on a server.
     
   • If SoftGrid 4.2 is used to deploy the application onto the server, it can be run by many users simultaneously, because each instance is running in a separate, isolated virtual layer.
     

This analysis leads to the architecture that is pictured in Figure 12:

Figure 12. Virtualizing a client-server application

The database will run on a Windows Server 2000 virtual machine, and it can continue to run on this virtual machine indefinitely. Running the database in a Windows Server 2000 virtual machine, which is installed on a Windows Server 2003 (or in the future Windows Server 2008) physical computer, allows the database to benefit from faster processors, faster IO subsystems, hot-swap drives and memory, and other leading-edge technology. It also simplifies the backup and recovery of the database, as the entire virtual machine is just backed up and restored.

The client application is run on a separate virtual machine, hosted on a central server. Based on the preceding analysis, it likely would create too many support requests and require too much hardware for the computer of each user to run the virtual machine on the local system of the user. Running the client application on a server-side virtual machine also allows easier backup, restore, and monitoring by the IT organization. This also keeps the legacy application from being a one-off solution, and keeps the legacy application from requiring special configuration of the computer of the user.

To allow multiple users to access the application simultaneously, the users connect to the virtual machine by using Terminal Services. Although the application was not designed for multiuser operation on a single computer, SoftGrid 4.2 provides isolation between each instance, so that multiple users can access the application simultaneously.

You might recall that the third example application is a help-desk three-tier application that is specified as follows:

• The application is mission-critical and must have near 100 percent uptime.
  
• The client UI is implemented in Visual Basic 6.0 and installed on over 200 user computers in a call center that is running Windows 2000.
  
• The application uses registry keys and local files on the host computer for personalization and customization purposes.
  
• The business rules are implemented in C++ and installed on a COM+ application server.
  
• The back-end database is implemented as a SQL Server database.
  
• Preliminary testing suggests that the application would run seamlessly on Windows Vista, but the computer hardware of the call center is at least six years old and is not Windows Vista–compatible. The company does not want to purchase new computer hardware just to keep the Visual Basic 6.0 application on a supported OS.
  
• The third example, a three-tier application, does not actually differ much from a virtualization perspective.
  

While apparently quite different from the two-tier application—with respect to scope, scale, availability, and so forth, from a virtualization perspective—the three-tier application is the same as the client-server application, except that a business-rules layer exists between the UI and that database. The same analysis that applied to the client-server application applies to the three-tier application, with the additional constraint that the three-tier application must be used by hundreds of users—making it completely unfeasible to deploy the UI in a virtual machine to each user. The UI application must be placed on a central server. The database can run on a server in a virtual machine, just as with the client-server application. The business rules, which typically run on a separate application server, can run also in a virtual machine.

Figure 13 shows the architecture:

Figure 13. Virtualizing a three-tier application

There is one critical difference, however: The two-tier application could run as multiple instances on the same virtual machine or physical computer. The three-tier application cannot run as multiple instances on the same computer; each user experience is customized by using local files and registry keys. The most efficient solution here is to use SoftGrid 4.2 to virtualize the application layer itself—allowing hundreds of users to access the application concurrently.

There is a workaround to using SoftGrid 4.2 application virtualization, which is available only as part of the Software Assurance support package that is found at http://www.microsoft.com/licensing/sa/default.mspx. For example, if the two-tier application accessed also local files and registry keys, the low number of concurrent users provides a workaround: With no more than 5 concurrent users out of 30, the company could have five or more virtual machines on the server that users could access via Terminal Services. This workaround would be cumbersome, however, with hundreds of concurrent users.

There are a number of options for preserving legacy applications. If the application is needed by very few users, and if the organization is small, it might make sense just to use Virtual PC to keep the application available. If the application is needed by more than a few users or comprises two or more tiers, or if the organization is large enough to have a data center and centralized IT, running the application on the server side makes more sense. In this architecture, the user accesses the application by using Terminal Services. If the application was not designed to be run on one computer by multiple simultaneous users, SoftGrid 4.2 can be added to the equation to provide isolation between the application instances.

Figure 14. Deciding on a design

Most applications fall into the categories that are discussed in this article and do not require any exotic configurations. Hopefully, the majority of legacy applications in your organization can be well-serviced by a combination of hardware, presentation, and application virtualization. However, there are specific "gotchas" that are worth pointing out before you travel too far down the path with an envisioned virtualization solution.

Applications with Hardware Constraints

Security Considerations