I have a sony vaio vgn-sz491n. i have loaded windows 7 professional, 64bit onto it. in the device manager, it shows that a driver for a mass storage controller is missing. where can i find this driver. keywords: sony vaio vgn-sz491n windows 7 professional 64bit 64 bit missing mass storage controller driver

Most likely missing a driver for SD/MC card reader
The problem is that Sony doesnt offer drivers for 64-bit windows so the other 32-bit drivers will not be compatible.
You have the options to install the windows versions supported by sony from esupport.sony.com (Vista or XP)
Or try installing windows 7 32-bit and installing the missing drivers from esupport (Vista section) as usually they are compatible.
If the driver is still missing you will need to update the driver from device manager (previously installed from esupport) and then select to browse or select a location, which will be %temp% or what is the same the temp folder for your account C\users\your_user_name\appdata\temp. This folder is usually hidden but it will work if you just type %temp%