BC guys -- will the dual boot be able to use the one Windows 7 System Reserved partition? Or, can each Windows 7 partition have its own set of Windows 7 boot files? I know the System Reserved will be marked Active, how will the two twin boot set be marked? I'd like to learn more about this.
All depends on how you set it up the multiboot.
The traditional way is to leave all drives hooked up when you install the second OS. As part of this process, the Windows installer (or other OS installer) will also install a boot manager on the primary boot drive. The boot manager will then load when you fire up the computer. You then select which OS you want to use and the boot manager will then "point" to the correct drive or partition (depending on if you installed the second OS on a second drive or just on another partition on the main drive) for the boot process to complete. I honestly don't know if going this process when using two installs of Windows 7 will just use a single Windows 7 System Reserved partition or two as I don't use this method...and don't have a system setup with two installs of Windows 7.
The other way is to do it the way that I do. With this method you are essentially setting up multiple single boot drives (however many different OSs you want to run) and then using either the boot priority in the BIOS or the boot drive select from your motherboard. You do this process buy disconnecting all drives from the computer other than the bare drive that you are going to install the new OS on. So, when you install the OS on the new bare drive, no other boot drives are detected by the Windows (or other OS) installer. As a result, it will NOT install a boot manager. As long as you do this for each different OS boot drive that you want to have, then each drive is setup like there will be only one boot drive. Then you are just using the motherboard boot options to select which drive the motherboard will try to boot from. This has the same effect as if you had your drives sitting out on the desk and you decide which drive you are going to install in the computer to boot from today...except with out actually having to open up the computer to remove one drive and install another drive if you want to boot from another OS. When you do select one drive to boot from using the motherboard boot options, the other drives will mount in Windows as if they are just additional disks. My older Windows desktop is setup this way with 4 different interior drives installed with 4 different OSs (two installs of XP, one install of Vista, and one install of Windows 7) plus a fifth drive in an external drive eSATA drive dock with Windows 8 on it (there are two other internal drives in RAID 1 for data). I do this option because adjusting the boot manager if you decide to delete/modify an OS can be a real pain in the rear. With this option, if I decide I don't want an OS anymore, I just remove the drive (and if I want to use it for something else, then reformat it as well). With this option, each disk will have any partitions needed by Windows just as if it was the only boot disk. So, if I did install Windows 7 twice, then there would be a Windows 7 Reserved partition on each disk.