Yes, you can target both x86 and x64 with the same code base in the same project. In general, things will Just Work if you create the right solution configurations in VS.NET (although P/Invoke to entirely unmanaged DLLs will most likely require some conditional code): the items that I found to require special attention are:
- References to outside managed assemblies with the same name but their own specific bitness (this also applies to COM interop assemblies)
- The MSI package (which, as has already been noted, will need to target either x86 or x64)
- Any custom .NET Installer Class-based actions in your MSI package
The assembly reference issue can't be solved entirely within VS.NET, as it will only allow you to add a reference with a given name to a project once. To work around this, edit your project file manually (in VS, right-click your project file in the Solution Explorer, select Unload Project, then right-click again and select Edit). After adding a reference to, say, the x86 version of an assembly, your project file will contain something like:
<Reference Include="Filename, ..., processorArchitecture=x86">
<HintPath>C:\path\to\x86\DLL</HintPath>
</Reference>
Wrap that Reference tag inside an ItemGroup tag indicating the solution configuration it applies to, e.g:
<ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|x86' ">
<Reference ...>....</Reference>
</ItemGroup>
Then, copy and paste the entire ItemGroup tag, and edit it to contain the details of your 64-bit DLL, e.g.:
<ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|x64' ">
<Reference Include="Filename, ..., processorArchitecture=AMD64">
<HintPath>C:\path\to\x64\DLL</HintPath>
</Reference>
</ItemGroup>
After reloading your project in VS.NET, the Assembly Reference dialog will be a bit confused by these changes, and you may encounter some warnings about assemblies with the wrong target processor, but all your builds will work just fine.
Solving the MSI issue is up next, and unfortunately this will require a non-VS.NET tool: I prefer Caphyon's Advanced Installer for that purpose, as it pulls off the basic trick involved (create a common MSI, as well as 32-bit and 64-bit specific MSIs, and use an .EXE setup launcher to extract the right version and do the required fixups at runtime) very, very well.
You can probably achieve the same results using other tools or the Windows Installer XML (WiX) toolset, but Advanced Installer makes things so easy (and is quite affordable at that) that I've never really looked at alternatives.
One thing you may still require WiX for though, even when using Advanced Installer, is for your .NET Installer Class custom actions. Although it's trivial to specify certain actions that should only run on certain platforms (using the VersionNT64 and NOT VersionNT64 execution conditions, respectively), the built-in AI custom actions will be executed using the 32-bit Framework, even on 64-bit machines.
This may be fixed in a future release, but for now (or when using a different tool to create your MSIs that has the same issue), you can use WiX 3.0's managed custom action support to create action DLLs with the proper bitness that will be executed using the corresponding Framework.
Edit: as of version 8.1.2, Advanced Installer correctly supports 64-bit custom actions. Since my original answer, its price has increased quite a bit, unfortunately, even though it's still extremely good value when compared to InstallShield and its ilk...
Edit: If your DLLs are registered in the GAC, you can also use the standard reference tags this way (SQLite as an example):
<ItemGroup Condition="'$(Platform)' == 'x86'">
<Reference Include="System.Data.SQLite, Version=1.0.80.0, Culture=neutral, PublicKeyToken=db937bc2d44ff139, processorArchitecture=x86" />
</ItemGroup>
<ItemGroup Condition="'$(Platform)' == 'x64'">
<Reference Include="System.Data.SQLite, Version=1.0.80.0, Culture=neutral, PublicKeyToken=db937bc2d44ff139, processorArchitecture=AMD64" />
</ItemGroup>
The condition is also reduced down to all build types, release or debug, and just specifies the processor architecture.
Access modifiers
From docs.microsoft.com:
public
The type or member can be accessed by any other code in the same assembly or another assembly that references it.
private
The type or member can only be accessed by code in the same class or struct.
protected
The type or member can only be accessed by code in the same class or struct, or in a derived class.
private protected (added in C# 7.2)
The type or member can only be accessed by code in the same class or struct, or in a derived class from the same assembly, but not from another assembly.
internal
The type or member can be accessed by any code in the same assembly, but not from another assembly.
protected internal
The type or member can be accessed by any code in the same assembly, or by any derived class in another assembly.
When no access modifier is set, a default access modifier is used. So there is always some form of access modifier even if it's not set.
The static modifier on a class means that the class cannot be instantiated, and that all of its members are static. A static member has one version regardless of how many instances of its enclosing type are created.
A static class is basically the same as a non-static class, but there is one difference: a static class cannot be externally instantiated. In other words, you cannot use the new keyword to create a variable of the class type. Because there is no instance variable, you access the members of a static class by using the class name itself.
However, there is a such thing as a static constructor. Any class can have one of these, including static classes. They cannot be called directly & cannot have parameters (other than any type parameters on the class itself). A static constructor is called automatically to initialize the class before the first instance is created or any static members are referenced. Looks like this:
static class Foo()
{
static Foo()
{
Bar = "fubar";
}
public static string Bar { get; set; }
}
Static classes are often used as services, you can use them like so:
MyStaticClass.ServiceMethod(...);
Best Answer
The only perf advantage to running IIS on 64bit vevrsus 32-bit is to allow access to a much larger memory address space.
If you are doing normal ASPX page processing, then it's likely you don't need to address more than 4gb from any single process. Suppose you run in 32-bit mode with a web-garden with multiple worker processes on the same machine. In that case each process can address up to 4gb.
The big advantage can come when you perform caching. A 64-bit process can maintain a huge in-memory cache (assuming you have the 32GB or more of RAM to support it) to allow you to cache complex page content or data, on the web server. This allows perf gains when the data is more expensive to generate than it is to retrieve - for example if the data is an elaborated form (let's say the result of a monte carlo simulation), or if the data resides off-box and the network IO time is much more expensive than cache-retrieval time.
If you do not use caching, then 64-bit IIS is not going to help you. It will require 64-bit pointers for every lookup, which will make everything a little slower.
64-bit servers are much more effective when used for databases like SQL Server, or other data management servers (let's say, an enterprise email server like Exchange), than for processing servers, such as IIS or the worker processes it manages. With a 64-bit address space, servers that need to manage data can keep much more of that data in memory, along with indexes and other caches. This saves disk IO time and elaboration time when a query comes in. Most Web apps don't need to address more than 4gb from a single process.
Maybe a useful analogy: In transport, an large SUV is like a 64-bit machine, while a regular, compact passenger car is like a 32-bit server. You can carry much more stuff in a large SUV, and it has a larger towing capacity, seating for 8 people, and a GVWR of 8600 lbs. But with all that, you pay. The truck is heavier. It uses more fuel. If you are only carting around 2 people and one duffel bag, you don't need an SUV. You'll be better off with the smaller vehicle. It can be speedier and more efficient.