installationnet
I've had a little search and I was wondering if there is back compatibility for the .NET framework.
The real question is, if there's a program that uses .NET Framework 1.1, can I install 3.5 and be done, or do I have to install 1.1 and then if something uses 3.5 I have to install 3.5 as well?
The registry is the official way to detect if a specific version of the Framework is installed.
Which registry keys are needed change depending on the Framework version you are looking for:
Framework Version Registry Key ------------------------------------------------------------------------------------------ 1.0 HKLM\Software\Microsoft\.NETFramework\Policy\v1.0\3705 1.1 HKLM\Software\Microsoft\NET Framework Setup\NDP\v1.1.4322\Install 2.0 HKLM\Software\Microsoft\NET Framework Setup\NDP\v2.0.50727\Install 3.0 HKLM\Software\Microsoft\NET Framework Setup\NDP\v3.0\Setup\InstallSuccess 3.5 HKLM\Software\Microsoft\NET Framework Setup\NDP\v3.5\Install 4.0 Client Profile HKLM\Software\Microsoft\NET Framework Setup\NDP\v4\Client\Install 4.0 Full Profile HKLM\Software\Microsoft\NET Framework Setup\NDP\v4\Full\Install
Generally you are looking for:
"Install"=dword:00000001
except for .NET 1.0, where the value is a string (REG_SZ) rather than a number (REG_DWORD).
Determining the service pack level follows a similar pattern:
Framework Version Registry Key
------------------------------------------------------------------------------------------
1.0 HKLM\Software\Microsoft\Active Setup\Installed Components\{78705f0d-e8db-4b2d-8193-982bdda15ecd}\Version
1.0[1] HKLM\Software\Microsoft\Active Setup\Installed Components\{FDC11A6F-17D1-48f9-9EA3-9051954BAA24}\Version
1.1 HKLM\Software\Microsoft\NET Framework Setup\NDP\v1.1.4322\SP
2.0 HKLM\Software\Microsoft\NET Framework Setup\NDP\v2.0.50727\SP
3.0 HKLM\Software\Microsoft\NET Framework Setup\NDP\v3.0\SP
3.5 HKLM\Software\Microsoft\NET Framework Setup\NDP\v3.5\SP
4.0 Client Profile HKLM\Software\Microsoft\NET Framework Setup\NDP\v4\Client\Servicing
4.0 Full Profile HKLM\Software\Microsoft\NET Framework Setup\NDP\v4\Full\Servicing
[1] Windows Media Center or Windows XP Tablet Edition
As you can see, determining the SP level for .NET 1.0 changes if you are running on Windows Media Center or Windows XP Tablet Edition. Again, .NET 1.0 uses a string value while all of the others use a DWORD.
For .NET 1.0 the string value at either of these keys has a format of #,#,####,#. The last # is the Service Pack level.
While I didn't explicitly ask for this, if you want to know the exact version number of the Framework you would use these registry keys:
Framework Version Registry Key
------------------------------------------------------------------------------------------
1.0 HKLM\Software\Microsoft\Active Setup\Installed Components\{78705f0d-e8db-4b2d-8193-982bdda15ecd}\Version
1.0[1] HKLM\Software\Microsoft\Active Setup\Installed Components\{FDC11A6F-17D1-48f9-9EA3-9051954BAA24}\Version
1.1 HKLM\Software\Microsoft\NET Framework Setup\NDP\v1.1.4322
2.0[2] HKLM\Software\Microsoft\NET Framework Setup\NDP\v2.0.50727\Version
2.0[3] HKLM\Software\Microsoft\NET Framework Setup\NDP\v2.0.50727\Increment
3.0 HKLM\Software\Microsoft\NET Framework Setup\NDP\v3.0\Version
3.5 HKLM\Software\Microsoft\NET Framework Setup\NDP\v3.5\Version
4.0 Client Profile HKLM\Software\Microsoft\NET Framework Setup\NDP\v4\Version
4.0 Full Profile HKLM\Software\Microsoft\NET Framework Setup\NDP\v4\Version
[1] Windows Media Center or Windows XP Tablet Edition
[2] .NET 2.0 SP1
[3] .NET 2.0 Original Release (RTM)
Again, .NET 1.0 uses a string value while all of the others use a DWORD.
for .NET 1.0 the string value at either of these keys has a format of #,#,####,#. The #,#,#### portion of the string is the Framework version.
for .NET 1.1, we use the name of the registry key itself, which represents the version number.
Finally, if you look at dependencies, .NET 3.0 adds additional functionality to .NET 2.0 so both .NET 2.0 and .NET 3.0 must both evaulate as being installed to correctly say that .NET 3.0 is installed. Likewise, .NET 3.5 adds additional functionality to .NET 2.0 and .NET 3.0, so .NET 2.0, .NET 3.0, and .NET 3. should all evaluate to being installed to correctly say that .NET 3.5 is installed.
.NET 4.0 installs a new version of the CLR (CLR version 4.0) which can run side-by-side with CLR 2.0.
There won't be a v4.5 key in the registry if .NET 4.5 is installed. Instead you have to check if the HKLM\Software\Microsoft\NET Framework Setup\NDP\v4\Full key contains a value called Release. If this value is present, .NET 4.5 is installed, otherwise it is not. More details can be found here and here.
float and double are floating binary point types. In other words, they represent a number like this:
10001.10010110011
The binary number and the location of the binary point are both encoded within the value.
decimal is a floating decimal point type. In other words, they represent a number like this:
12345.65789
Again, the number and the location of the decimal point are both encoded within the value – that's what makes decimal still a floating point type instead of a fixed point type.
The important thing to note is that humans are used to representing non-integers in a decimal form, and expect exact results in decimal representations; not all decimal numbers are exactly representable in binary floating point – 0.1, for example – so if you use a binary floating point value you'll actually get an approximation to 0.1. You'll still get approximations when using a floating decimal point as well – the result of dividing 1 by 3 can't be exactly represented, for example.
As for what to use when:
For values which are "naturally exact decimals" it's good to use decimal. This is usually suitable for any concepts invented by humans: financial values are the most obvious example, but there are others too. Consider the score given to divers or ice skaters, for example.
For values which are more artefacts of nature which can't really be measured exactly anyway, float/double are more appropriate. For example, scientific data would usually be represented in this form. Here, the original values won't be "decimally accurate" to start with, so it's not important for the expected results to maintain the "decimal accuracy". Floating binary point types are much faster to work with than decimals.
Best Answer
Unfortunately you will have to install both versions. Older version of the framework are not automatically bundled with newer versions.