Question : 32 bit applications on 64 bit OS. What to expect as far as performance?

I have a new laptop that has a 64 bit processor (Core 2 Duo). I am considering installing 64 bit Windows 7 instead of the 32 bit version. Many of the development applications I run will still be 32 bit (Visual Studio 2008, Office 2007). Some other programs will be 64 bit (SQL Server 2008). At this point I only have 4 GB of RAM, however the laptop can go up to 8 GB of RAM. The cost of upgrading to 8 GB of RAM is why I am currently going to be staying at 4 GB. My question is this ... Should I expect to see a performance hit running 32 bit applications, such as Visual Studio 2008 and Office 2007, in a 64 bit OS environment? With only 4 GB of RAM would it be better to stay with a 32 bit version of Windows 7 until I obtain more RAM?

Answer : 32 bit applications on 64 bit OS. What to expect as far as performance?

First, I must give a note: it's not an Itanium; Itanium uses a very slow x86 emulation layer for 32-bit applications (relevant for all OSes).
Second, I did some performance testing for Linux and Solaris on the same machine with 64-bit CPU (Athlon 64). The application was very CPU and I/O hungry. Very. And its 32-bit version was 7-10% slower than 64-bit version.
I suppose that for Windows family the situation will be similar.

You need to understand for what sort of activity you need 64-bitness. Say, it's MSSQL. If it will be running *actively* all the time, then it may be worth of using 64-bit OS.

Also, you have an option to install 64-bit OS on your current machine without any hardware upgrade; just to see what's happening with other applications you need.