Referencing .net 1.1 assemblies from 64 bit applications

Question

I have to upgrade a project from 32 bit to 64 bit. My project is currently on .net 2.0 (will be soon 4.0, but doesn't really matter for this issue). My project is referencing some old .net 1.1 assemblies, that I only have in binary form. As you all know, 64 bit support was added in .net 2.0 only, and I expected my application won't run because of those old assemblies.

However, my application runs on a x64 server in 64 bit mode (no star is shown in Task Manager) while referencing the .net 1.1 dll.

My questions are:

1. Why does it run? I previously read that you cannot use .net 1.1 assemblies in 64 bit apps.
2. Are there any shortcomings if I keep the 1.1 assemblies? Or should I invest effort in getting newer versions of those 1.1 assemblies?

EDIT: I forgot to mention that a requirement is to run the application (asp.net) natively in 64 bit. The application runs in 64 bit because I disabled 32 bit compatibility on my application pool.

EDIT2: I just tried to compile and run the application compiled for x64. It works. So it runs in pure 64 bit mode, no questions about it.

Answer 1

A .NET 1.1 assembly contains the same kind of IL as a .NET 2 or .NET 4 assembly. Only the format of the metadata has changed. The jitter doesn't mind translating it to 64-bit machine code and the CLR can read the old metadata format. Only if the .NET 1.1 assembly contains native code will you have a problem. Corflags.exe utility, ILONLY bit. There's no compelling reason to rebuild that assembly.

Answer 2

Is your application running under wow32 (32-bit emulation mode)? Most applications do not really run in x64 mode, they force the application to run in wow32 (x86 mode) to keep their backward compatibility on older x86 systems. Otherwise the application would run only on x64 systems but not on x86.

Forcing the application to run in x86 mode (even on x64 systems) allows to run ony any manchine no matter if its a 32 or 64 bit windows OS.