What is the difference between windows 7 sp1 & Windows 8.1 aside from Metro apps?

Some of the most notable differences:

• Start button opens a Start Screen instead of a Start Menu (basically a tiled, full-screen Start Menu)
• Improved search from Start Screen (as opposed to Start Screen searching in Windows 8 or Start Menu searching in Windows 7)
• Windows 8 Pro includes the client Hyper-V - a HUGE (cannot overstate) improvement over Windows 7's Virtual PC
• Windows 8 starts up quicker and runs more efficiently than Windows 7
• Windows 8 gives you the ability to change the "lock screen" (where you sign in) from within Windows (instead of registry changes)
• Simplified interface for many functions (printers, updates, wireless, etc.), although the "normal" (advanced) interfaces still exist
• Microsoft Skydrive is integrated into the OS, instead of installed as an app
• Signing in via Microsoft/Hotmail account allows you to synch user profile data
• Native ISO support
• Metro apps (full-screen apps that come from the Windows Store and run from the Start Screen

There are others, I'm sure, that I'm leaving out, but these are the most notable from the top of my head.  Obviously, how beneficial the differences/upgrades are are going to depend on what you are going to use it for and what you are comfortable with.

"I also heard Microsoft is trying to make the Operating system into a subscription service like they do for office 365--I hope that is not the case."

Absolutely not the case with Windows 8.x.  Office 365, while marketed primarily as a subscription, is not sold exclusively so.

There are a few things missing from Windows 8.1 not mentioned and many of the newer features some users find a hindrance while other users love the changes:

• No Windows XP for compatibility with older programs as was present in 7 Professional/Ultimate.
• In addition Media Centre is removed from Windows 8.1 and is a paid upgrade: http://windows.microsoft.com/en-gb/windows-8/feature-packs you for some reason need to pay for Professional to get it despite Media Centre being more of a Home user product.
• No native DVD playback: http://windows.microsoft.com/en-gb/windows/dvd-playback-help
• Games such as Chess Titans are removed: http://answers.microsoft.com/en-us/windows/forum/windows_8-gaming/wheres-chess-titans-in-windows-8/c2ec442d-5763-4168-b7e3-89afe464c996
• Start Menu → Start Screen which is fine in my opinion if customised correctly: http://dellwindowsreinstallationguide.com/a-clean-install-of-windows-8-1/customising-windows-8-1/ Sadly however there is no way to get this back natively without installation of 3rd party addins such as Start8: http://dellwindowsreinstallationguide.com/a-clean-install-of-windows-8-1/customising-windows-8-1/stardock-start8-and-modernmix/
• Metro Apps which in my opinion are a complete invasion of the "Windows" experience, in particular Metro IE (again explained here): http://dellwindowsreinstallationguide.com/a-clean-install-of-windows-8-1/customising-windows-8-1/ I generally avoid the use of Metro Apps or use 3rd party addins like ModernMix to make them Windows: http://dellwindowsreinstallationguide.com/a-clean-install-of-windows-8-1/customising-windows-8-1/stardock-start8-and-modernmix/ The inbuilt Metro Reader can only open one document at a time for instance and is highly annoying.
• SkyDrive for Windows is integrated although in my experience the Desktop application does not work as well as the one for Windows 7.
• Microsoft Security Essentials is integrated natively which is a huge bonus making Windows 8.1 very secure however context menus are lost and there is no notification tray icon for it.
• Under the hood performance enhancements.
• .iso is opened under Windows Explorer.

Actually, there is suppose to be xp compatibility with 8.1 but you may have to change architect if you use a 64 bit machine.  8.1 pro can change a 64 bit to a 32 bit install.   The only downside or plus side you have to use the 8.1 default drivers.    I could careless about the windows store or apps.  I will apply the UAC hack via registry.   That should boot you directly into the desktop.   I don't use security essentials,  I use third parties.   The only thing is the "DVD" player issue.  Dell didn't include the "Power" dvd player on this system.

"No Windows XP for compatibility with older programs as was present in 7 Professional/Ultimate."

XP Mode (XP virtual machine) is absent, but XP "compatibility mode" is still present ... EVEN in the 64-bit version.

"Metro Apps which in my opinion are a complete invasion of the "Windows" experience"

This depends.  If you are planning to run an app full-screen anyway (like Netflix or a game), then it isn't an invasion (nor is it any different from a desktop app in any version of Windows).  Personally, I agree with nat on "some" apps, most notably the PDF Reader - I use Adobe's PDF Reader (which I also hate, but less than the "metro" Reader).  Metro apps can also be run in a partial screen, instead of full-screen.

"◦SkyDrive for Windows is integrated although in my experience the Desktop application does not work as well as the one for Windows 7."

I have not had any issues with Skydrive.

"8.1 pro can change a 64 bit to a 32 bit install."

No, it can't.  Not on the fly ... it requires a clean install, as Windows always has when changing architecture.

"I will apply the UAC hack via registry.   That should boot you directly into the desktop."

Huh?!  Windows 8.1 gives you the ability to boot directly to the Desktop.  Registry hacks aren't needed, especially "UAC" hacks.

"I don't use security essentials,  I use third parties."

The AV you use is up to you, but I second nat's approval of Microsoft Defender (built-in Security Essentials).

"according to some MSFT poster"

Ha ha ... anyone can create an account and post on Microsoft boards :)

"The Windows 8.1 professional edition has or was suppose to have a virtual machine,  so that you run older programs in Windows xp mode."

XP Mode belongs to Windows 7, exclusively.  Windows 8 and 8.1 (Pro only) includes virtualization software called Hyper-V.  Hyper-V can be used to virtualize nearly any operating system for which you have a valid license.  Windows 8 does NOT include a license for XP, either as a downgrade or as a virtual machine (like Windows 7 did), so you would have to have a valid license or purchase one.  Virtualization isn't just used for compatibility reasons, but also for testing/validation, ease of management/deployment, a modern replacement for many "dual-boot" scenarios, etc.

XP compatibility mode is different ... it is changed under Properties, Compatibility tab for the file/shortcut.  This only changes the way the file behaves (or Windows behaves in relation to the file).  This is the only compatibility mode that Windows 8 has specifically for XP.

"If you have a 64 bit machine,  you have to change the architecture to a 32 bit  machine before xp mode will show,   If not,  you can download virtual machine at Microsoft website if it still is there."

Again, changing from 64-bit to 32-bit requires a clean install (your wording was unclear and made it sound like you could simply "switch"), but even the 32-bit version does NOT give you access to XP Mode (I.e. the XP virtual machine, licensed to Windows 7, available for download from Microsoft.com).  (In fact, 32-bit versions of Windows running virtual machines, regardless of software (VMware, Vbox, Hyper-V) are more limited - you cannot run 64-bit virtual machines if your host OS is 32-bit, and obviously, you wouldn't have more than 4GB of RAM total to use between your host and any virtual machines.)

Actually,  according to some MSFT poster.    The Windows 8.1 professional edition has or was suppose to have a virtual machine,  so that you run older programs in Windows xp mode.    If you have a 64 bit machine,  you have to change the architecture to a 32 bit  machine before xp mode will show,   If not,  you can download virtual machine at Microsoft website if it still is there.

I already knew you had to do a clean install if windows 8.1. to change the architecture.   I didn't say you can do it on the fly,

Now it is getting confusing.   We are both correct.   The reason were are talking about two different things.   I wasn't talking about the compatible mode of xp,  I was talking about the virtual machine that would allow you to install windows xp with windows 8.1 but you would need the pro version.  Also,  if you system is a 64 bit,  it may need to be changed to 32 bit but that requires a clean install.

Of course you need license to install operating system,  that a given.

"I wasn't talking about the compatible mode of xp,  I was talking about the virtual machine that would allow you to install windows xp with windows 8.1 but you would need the pro version"

That is called Hyper-V - the built-in software (Pro only) that allows you to install, configure, and run virtual machines, including XP.  HOWEVER, with Hyper-V, you MUST have your own, unused, and valid license for the OS.  There is NO pre-configured Windows XP virtual machine that you download from Microsoft that can be run in Windows 8.x ... there IS one for Windows 7 Professional (or higher), but NOT for Windows 8.x.  It belongs exclusively to Windows 7, by license.

I'm still not sure why you are talking about the 64-bit vs. 32-bit thing ... changing Windows 8.1 from one to the other will change nothing related to the above situation.