Legacy Software Support

From Mac vs. Windows

Both Windows Vista and Mac OS X permit you to run applications designed to run on earlier operating systems. This is important, because when a user decides to upgrade their OS, they can continue to use the same applications if they choose to.

Mac OS X

Legacy Support on Power PC (PPC) Macs

Mac OS X Leopard no longer supports the Classic environment, thus making it incapable of running pre OS X applications.

Legacy Support on Intel (x86) Macs
Intel chips in new macs use x86 architecture which is completely different from the Power PC architecture used on older Macs. Many current applications use universal binaries, which means the applications contain code to run on both x86 and PPC hardware. For running PPC code, there is a emulator named Rosetta

This technology allows PowerPC applications to run on top of x86. Rosetta is a built-in part of OS X, so it is fully automatic and seamless - the user does not need to take any extra steps to get a PowerPC-only application to run in such a manner. Rather, they simply launch it as they always would, and Rosetta invisibly translates the application's instructions so that they work with the Intel processor. However, this translation process eats up additional CPU power, so applications that run under Rosetta will suffer from a decrease in speed when compared to how they would run on a PowerPC chip. In addition, according to Apple's documentation, Rosetta is incapable of running the following:

• Screensavers written for the PowerPC
• System Preference add-ons
• Applications which specifically require the PowerPC G5* Kernel extensions
• Java applications with JNI (PowerPC) libraries

Windows Vista

Windows Vista ships in both 32-bit and 64-bit versions.

Legacy Application Support in 32-bit versions
Since Windows Vista is an upgrade over Windows XP, in theory most programs designed to work in earlier Windows versions should also work in Vista. This includes programs designed for the NT platform (NT 3.5, NT 4, 2000, XP, Server 2003). Also, because of how Windows 9x (Windows 95, 98, and ME) was designed, the majority of program from that era should also work.

In reality, there are a number of issues with legacy application support. Older system utilities usually will not work due to changes in both the operating system and the file system used. Many older Win9x apps were designed for a system without multiple users, so they may not be aware of the multi-user nature of Windows Vista and may be required to run with elevated privileges. Other programs may try to overwrite various system DLLs. Windows Vista will recover a system file if it was overwritten. Lastly, some programs may require the operating system to behave in a similar manner to an older version of Windows. If this happens you can run the application under compatibility mode. To do so, right click on the application and select properties, and then go to the Compatibility tab. Then, select the version of Windows the application works under. The application will then "think" it is running under that version of Windows.

In order to support 16-bit programs that ran under DOS and Windows 3.x, Vista uses NTVDM and WoW technology.

NTVDM stands for NT Virtual DOS Machine. What it does is run DOS programs by emulating MS-DOS. It also allows custom legacy version of autoexec.bat and config.sys to be assigned to each program in order to help with emulating the exact requirements the program may need. One drawback of this is that MSDOS program cannot access hardware, because of that fact, certain things like sound support in game may or may not work

WoW stands for Windows On Windows. It works similar to how NTVDM works and provides an emulated Windows 3.x (3.0, 3.1 and Windows for workgroups) environment. There is one major drawback to this. Windows 3.x programs do not understand Vista's long filenames and only understand the old 8.3 (eight characters for name and 3 characters for file extension) file names. To help combat this problems, Vista generates a 8.3 name to every file on the fly that the programs tries to access. While this allows the old program to work, the resulting file names can be cryptic. A file called "2007 budget report.doc" may show up as "2007bud~1.doc".

There is also one additional drawback to all legacy support. Older programs may behave in such a way that does not work with the desktop Window manager which provides the Aero Interface. If Vista encounters such a program, it disables the Aero interface in order to run that program, and turns it back on after its finished.

Legacy Application Support in 64-bit versions
The 32-bit editions of Vista are all limited to accessing a maximum of 4GB of RAM. To address this need and to take full advantage of 64-bit processors, Microsoft produces 64-bit versions of all editions of Vista except Starter Edition. Different editions can access different amounts of RAM in their 64-bit versions. Home Basic supports 8GB, Home Premium supports 16GB, and Business and Ultimate support 128GB+. For 32 bit programs, there is a different version of WoW that emulates the 32-bit version of Vista.

This results in a number of drawbacks. There is no support at all for 16-bit (windows 3.x and MSDOS) programs. Vista does however have some very limted support for popular 16 bit installers that some 32 bit programs may use. 32 bit drivers do not work and require 64 bit versions. 32 bit ActiveX controls will not work in the 64 bit version of Internet Explorer (Vista also supplies a 32 bit internet explorer version to help in this situation)

Emulation
There is also another option. Microsoft provides Virtual PC 2007 [1] as a free download. This program will allow you to emulate all the hardware in a 32-bit PC. This allows old legacy operating systems inside the OS, similar to the way Classic in OSX works. To help with this, Microsoft offers a full version of Windows XP on a virtual hard drive[2]. The hard drive image is set to expire within 6 months of being released, but Microsoft has said they will refresh it at that date for another 6 months. However, this does not limit the user to XP. Almost every 32-bit or 16-bit operating system that runs on x86 hardware is supported. This included Windows 3.1, Windows 95, IBM OS/s, and even Linux. None of these, however, are available from Microsoft, and require you to own the original install media.

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