256gb SSD for 2 os in dual boot

Longevity of the card will not be affected.

However....
1. Why both the 32bit and 64bit Win 7? I see little need for this. The 64bit will run 32bit software.

2. Partition size. A bare Win 7 64bit with all current updates is around 45GB. Presumably you will want to install some applications with that? 70GB is going to look mighty slim.

3. You also need to leave 10-15% free space on that drive for the TRIM function to do its thing. So don't go over 200GB used space.

By all means you can put the other OS on the HDD instead of splitting the SSD. No problem at all.

So...split the SSD in half. 100GB each
Put Win 7 64bit in one, and games or whatever in the other.

On the HDD, Win 7 32bit and whatever incompatible applications you need that for.

Can you confirm which 32 bit programs you have and use that do not run on Windows x64? Win 32 should run **16** bit programs whereas Win 64 will not, but Windows 64-bit has a 32 bit emulator (WOW - Windows on Windows) that should let it run 32-bit programs.

If indeed you can run those programs on Windows x64, then I highly suggest simplifying your life and just using Windows x64.

If it turns out you actually meant 16 bit programs (some real legacy stuff), or there is some incompatibility with 32-bit programs then I'd consider using a Virtualbox install of Windows 32-bit inside your Windows 64-bit installation. So long as these 32-bit programs are 2D and not particularly CPU or RAM intensive (after all, 32 bit is limited to 4GB RAM) then you should be able to get away with this.

If you absolutely need 32-bit Windows and 64-bit Windows as a dual boot solution, I'd first estimate the relative usage. If you spend 80% of your time in 64-bit Windows and the rest in 32-bit, then I'd consider putting 64-bit on the SSD and leave it as one partition with the games on it and put 32-bit Windows on a HDD. If for some reason you want to run games in either 32-bit or 64-bit, then the 32-bit install would simply need to point to the SSD's games library (I'm assuming Steam here).

If, however, you find that the split is more like 50/50 then I'd probably split the SSD in two. For games, I'd consider a separate SSD altogether, maybe a 120GB one would hold enough of your current titles and those are pretty inexpensive these days.

Longevity of SSDs is mostly measured in rewrites, and typically quoted as a metric called DWPD -- drive writes per day. For example, a 240GB SSD rated for 2 DWPD would be able to write 480GB (240*2) every day for its rated warranty period, perhaps 3 years. This would be writes totaling over 500TB. Flash memory has an intrinsic lifetime as well, and you'll basically find that if you let an SSD sit unpowered for a year or so then it may have some read errors. So the basic idea is to use it at least infrequently and write to it but not an insane amount (really, only database or cloud storage hosts have to worry about the DWPD). As a rough estimate, a Samsung 850 Pro should be able to endure 0.4 DWPD for 5 years, which doesn't mean you can't put 200GB on it one day (0.78 of the capacity), it just means you shouldn't do that daily. Every other day would actually be OK.

Basic point: by the time your SSD would naturally die, it will be so horribly outdated you'll laugh at it. Already we see M.2 slots with 32Gb/s speed (PCIe 3.0 x4) and that blows away SATA at 600MB/s (2.4Gb/s). Consider how just in the last few years SSDs have gone from being something that's small and expensive (in 2009 a 4GB PCIe SSD cost $1500, in 2003 a 1TB SSD was invented costing $2,000,000) to completely mainstream and practically obligatory (120GB for $60).

That will work as just fine. In fact, it is preferable.
And it will NOT affect your boot time.

The question is....how do you want to choose which OS to boot into? This dictates how you install them.

2 options:
1. Let the Windows boot manager give you the option
or
2. You select in the BIOS which to boot from

I recommend #2. For this, install each OS with only that particular drive connected while you do the install.
Install the 32bit onto the HDD
Disconnect, connect the SD, install the 64bit.

On powerup, F12 (or whatever it is on your system) and select which drive/OS.

In your BIOS....after all the installation noted above.
Have the SSD first in the boot order.
If you need to go into the 32bit OS, reboot and select that drive in the BIOS.

If your system currently has Windows showing you what to boot into, then you've installed the two OS with both drives or partitions connected.
This slows down your booting process, because it waits for the preset amount of time for you to choose.

If most of the time you're using the 64bit, that is needless wait time.

You could also think about a whole different concept, and put the 32bit OS in a VirtualMachine.

You're installing each OS with only that target drive connected. It doesn't matter which one first.

Yes and yes.

Not in the least. That is what my current systems is....250GB Samsung 840 EVO.

Correct. OS (Win 8.1 Pro) and just about all applications, apart from games.
Just recently moved from a 120GB which was just getting too small. And it was 3 years old....

No...no problems at all.
Why no games on it? The old 120GB drive was simply too small. 80GB of games obviously did not work with that. SO the games lives elsewhere.
So the drive got to around 85GB used space, and I cloned it to the 250GB.
Still...not large really enough to hold all the games. Sure, I could, but since gaming is very much a secondary use...I have not seen the need.

And since all the games I play are single player, them living on the HDD doesn't really matter. There is no 'someone else' to respawn faster than me.

Buying today? Get the 850 EVO.
I have 3 SSD's in this PC.
250GB 840 EVO (OS and applications)
250GB 840 EVO (photo work)
120GB Kingston HyperX 3k (currently empty, unknown usage)

(and other HDD's - games, backups, etc)
I'm still in the process of moving stuff to whichever drive will work best.