|You can set up Windows 7 and XP on the same computer, but there are some things you need to be made aware of. |
It doesn't matter if Windows 7 or XP is "primary" or "secondary". You can only boot one of them on a computer at time.
The best way to set up a dual boot system is to install Windows from scratch, on one or more blank drives - install XP first, make all NTFS partitions with XP, then install Windows 7.
However, you can set up a dual boot configuration in any case.
If you use the dual (multi) boot feature built into XP or Windows 7 to dual boot with, by default, ALL the System Restore restore points in Windows 7 (or Vista) are DELETED, EVERY TIME you boot XP. If that concerns you, Microsoft has only two workarounds for that situation - one is you use the BitLocker feature, but that's only available to you if you have the Ultimate or Business version of Windows 7 (or Vista) - the other workaround may not work in all situations.
I got around that, for dual booting Vista Premium and XP MCE 2005, by using a paid third party boot manager program that can be configured to HIDE Vista's (in your case Windows 7's ) Windows partition from XP while booting XP - BootIt! N.G.
Vista and Windows 7 use a slightly different NTFS version than XP and 2000 do. XP cannot see NTFS partitions that were made by Vista or Windows 7 (in My Computer or Windows Explorer) , but Vista or Windows 7 can see NTFS partitions that were made by XP or 2000 fine (in Computer or Windows Explorer) .
If you were starting over from scratch, you could install XP first and make all NTFS partitions with XP, but that presents a problem if you want to keep at least your present Windows 7 Windows partition (the one Windows 7's Windows was installed on) data contents intact.
( You could make a NTFS partition in XP on un-allocated drive space, or if you don't have any, on un-allocated drive space made available by shrinking an existing partition in Windows 7's Disk Management, then copy your pictures, documents, etc. to that, then delete the Windows 7 made partition the pictures, documents, etc were on and remake a NTFS partition in XP . The partitions can be merged if they're beside each other on a hard drive, or made larger or smaller in XP by you using a third party "partition manipulation" program, as long as you're not trying to merge two partitions that each have an operating system on them. However, Vista and Windows 7 can react badly if you move the data on their Windows partition or change the size of the partition in anything other than Vista or Windows 7, or a "partition manipulation" program that is 100% Vista or Windows 7 compatible. )
Vista and Windows 7 always see the first installation of them as being installed on C, for their Windows partition, no matter which partition you install them on, no matter which hard drive partitions are already present when you run Setup.
XP, on the other hand, only assigns C to the partition it's Windows is installed on if Setup does not detect any other hard drive partitions as having already been assigned drive letters when Setup is run. If that concerns you, if you want to have XP seeing it's Windows partition (the one XP's Windows is installed on) as being installed on C, you either have to install it on a blank drive, disconnect any other hard drive, BEFORE you run XP's Setup, or you have to use a "partition manipulation" program to HIDE all other existing hard drive partitions on drives connected to the computer BEFORE you run XP's Setup.
E.g. the freeware Easeus Partition Master Home Edition.
All versions of XP except 64 bit Pro are 32 bit operating systems - they can't use more than 4gb of ram, and even then they can't use all of the 4gb for programs. I assume since you have 6gb of ram that you have a 64 bit version of Windows 7.
The 4gb virtual memory address limit for 32 bit operating systems.
An example of 3gb working better than 4gb in a 32 bit operating system.
See Response 6:
jam's explanation refers to links on other sties: