Windows Server 2008 (codenamed "Longhorn") and its successors represent distinct milestones in Microsoft's server OS evolution. The original 2008 release (build 6001) introduced Server Core and Hyper-V virtualization, while 2008 R2 (build 7600) marked the transition to a 64-bit-only architecture based on Windows 7's kernel.

2008 SP2 (released in 2009) primarily delivered security updates and bug fixes rather than architectural changes. Key improvements included:

• Support for 256 logical processors (up from 64)
• VHD boot capability
• Power management enhancements

2008 R2 introduced fundamental changes that impact developers:

// Example: PowerShell 2.0 cmdlet availability check
if ((Get-Host).Version -ge [version]"2.0") {
    Write-Host "R2-specific features available"
} else {
    Write-Host "Running on original 2008"
}

When developing for mixed environments, consider these critical testing areas:

1. PowerShell Versioning: R2 includes PowerShell 2.0 with remoting capabilities
2. WCF Bindings: Net.TCP port sharing requires R2
3. Hyper-V Management: R2 adds Live Migration

Here's how to handle version detection in C#:

using System;
using Microsoft.Win32;

class OSVersionCheck {
    static void Main() {
        RegistryKey key = Registry.LocalMachine.OpenSubKey(
            @"SOFTWARE\Microsoft\Windows NT\CurrentVersion");
            
        string productName = (string)key.GetValue("ProductName");
        string csdVersion = (string)key.GetValue("CSDVersion");
        
        Console.WriteLine($"OS: {productName}");
        Console.WriteLine($"Service Pack: {csdVersion ?? "None"}");
        
        if (Environment.Is64BitOperatingSystem) {
            Console.WriteLine("Running on 64-bit architecture (R2)");
        }
    }
}

For maximum compatibility:

• Target .NET Framework 3.5 SP1 (included in all versions)
• Avoid R2-specific WMI namespaces like root\virtualization\v2
• Use feature detection rather than OS version checks when possible

Windows Server 2008 (original release) and 2008 SP2 share the same NT 6.0 kernel, with SP2 being a cumulative update package. Windows Server 2008 R2 represents a significant architectural shift with these key differences:

// Kernel version check example
if (osVersion.Major == 6 && osVersion.Minor == 0) {
    // Windows Server 2008 or 2008 SP2
} else if (osVersion.Major == 6 && osVersion.Minor == 1) {
    // Windows Server 2008 R2
}

R2 introduced several developer-relevant changes:

// PowerShell version check
$psVersion = $PSVersionTable.PSVersion
if ($psVersion.Major -lt 2) {
    Write-Host "Original 2008 (PowerShell 1.0)"
} else {
    Write-Host "2008 R2 (PowerShell 2.0+)"
}

Three critical areas requiring attention:

// Example of API availability check
[DllImport("kernel32.dll")]
static extern bool IsWow64Process(IntPtr hProcess, out bool wow64Process);

try {
    bool retVal;
    if (Environment.OSVersion.Version.Major >= 6 && 
        Environment.OSVersion.Version.Minor >= 1) {
        // 2008 R2 specific code
        IsWow64Process(Process.GetCurrentProcess().Handle, out retVal);
    }
} catch (EntryPointNotFoundException) {
    // Fallback for original 2008
}

For .NET applications, consider these manifest settings:

<assembly manifest>
  <compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">
    <application>
      <!-- Windows Server 2008 -->
      <supportedOS Id="{35138b9a-5d96-4fbd-8e2d-a2440225f93a}"/>
      <!-- 2008 R2 -->
      <supportedOS Id="{1f676c76-80e1-4239-95bb-83d0f6d0da78}"/>
    </application>
  </compatibility>
</assembly>

SMB 2.1 differences require special handling:

// Network share access example
string uncPath = @"\\server\share";
if (Environment.OSVersion.Version >= new Version(6, 1)) {
    // Use SMB 2.1+ optimizations for R2
    UncAccessWithSMB21(uncPath);
} else {
    // Fallback to basic SMB
    BasicUncAccess(uncPath);
}