With the advent of Windows 8 Microsoft will support both traditional x86 processors and new System on a Chip (SoC) architectures, including ARM systems.The traditional Windows 8 release, designed as the successor of Windows 7 will play nice with existing CPUs, as well as current hardware and software, but will also be compatible with legacy products, especially with older applications.
In contrast, Windows 8 for SoC will not offer compatibility or legacy application support.
According to Renée J. James, Senior Vice President, General Manager, Software and Services Group (via Channel Register), Windows 8 traditional will also feature a Windows 7 Mode.
“Windows 8 traditional means that our customers, or anyone who has an Intel-based or an x86-based product, will be able to run either Windows 7 mode or Windows 8 mode," James revealed. "They'll run all of their old applications, all of their old files – there'll be no issue.
"On ARM, there'll be the new experience, which is very specifically around the mobile experience, specifically around tablet and some limited clamshell, with no legacy OS. Our competitors will not be running legacy applications. Not now. Not ever."
When I first heard of the move, I could not help asking myself what exactly is Windows 7 Mode in Windows 8?
Customers can already access a Windows Mode when running Windows 7. I’m of course talking about Windows XP Mode, the free, virtualized copy of XP SP3 designed to run inside Windows Virtual PC virtual machines.
James’ mention of Windows 7 Mode could point to a similar virtualized copy of Windows 7 designed for Windows 8 customers.
This brings me to my next question. Why?
And I must tell you that the Windows 7 Mode in Windows 8 has really left me scratching my head. Windows XP Mode is designed specifically to run programs that are incompatible with Windows Vista and Windows 7.
The evolution from XP to Vista brought with it a series of breaking changes, especially around having users run with standard privileges and not as admins.
However, there were no compatibility issues between Windows Vista and Windows 7. In fact, the rule was that customers that upgraded to Vista would experience a hassle free migration to Windows 7.
From what I gather, Microsoft has the same strategy for the evolution from Windows 7 to Windows 8. No breaking changes.
Even the versioning of Windows vNext is designed to reflect this. Windows 7 was essentially Windows 6.1. Windows 8 will be Windows 6.2.
Then why the need for a Windows 7 Mode? Could this mean that there WILL BE breaking changes in terms of compatibility and legacy app support introduced in Windows 8? Otherwise why would applications designed for Windows 7 be considered legacy or be incompatible?
The only scenario that I can think of involves the development of security barriers in Windows 8. New security measures / mechanisms / features that would change the way in which applications run in Windows 8 compared to how they were running in Windows 7 and earlier. But this is all speculation on my part.
UPDATE: Windows 8 Leaked Details Denied by Microsoft.