What is the meaning of "downlevel_mainfest" registery item?

[1400700226]

Hi teachers,

I am a geek that always want to find out the principle.

Today I have a new problem:

After installing the VC2005SP1 runtime in WinXP SP3,

in the registery 
"HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SideBySide\Installations",

 

there are items like
"x86_Microsoft.VC80.CRT_1fc8b3b9a1e18e3b_8.0.50727.6195_x-ww_44262b86",

and, there are sub item
"downlevel_manifest.8.0.50727.6195" and "downlevel_payload.8.0.50727.6195"

in item "x86_Microsoft.VC80.CRT_1fc8b3b9a1e18e3b_8.0.50727.6195_x-ww_44262b86".

http://i.imgur.com/V2vUsGJ.jpg

So, things that I want to know are:

What is the use of these registery item like "downlevel_manifest.8.0.50727.6195"?
What program will use them?
What is the meaning of "downlevel" in registery there?
What will be abnormal if I delete the items like "downlevel_manifest.8.0.50727.6195"?

Thanks!

[Israeli_Eagle]

https://en.wikipedia.org/wiki/Side-by-side_assembly

[macnavarra]

In Windows, software that rely on Windows Side-by-Side (WinSxS) need an application manifest. It is either an  file with .manifest that accompanies  or is an integral part of them, in the same XML format. It bears, name, version, trust information, privileges required for execution and dependencies on other components.

An assembly manifest is very similar to an application manifest but describes the identity of components known as "assemblies". These assemblies are referred to in the application manifest.

An example of an application manifest is as follows. This application manifest has two core parts: Security and dependency. The security part says that the application requires "asInvoker" security level; i.e. it is okay with whatever security level it is executed. The dependency part say the application needs a component called "Microsoft.VC90.CRT" with version number "9.0.21022.8".