Does having TRIM enabled affect other hard drives on a computer (and how do you know when Windows is using it)?

The SU thread How do I know if my SSD Drive supports TRIM discusses this same question.

This answer remarks that "DisableDeleteNotify=0" means that TRIM is enabled in Windows. This only means that TRIM commands will be sent to the disk driver, which might either ignore it or send it to the firmware, which in its turn will either ignore it or use it to good effect.

So it seems that you have done all that is necessary in Windows. Windows will send TRIM commands to the disk driver. However, there is actually nothing further that you can do to verify that it is actually working. There are no benchmarks or other tests that really test the TRIM functioning of the disk driver or the firmware. If you find in the future that Write operations are too slow on the disk, then this means that it is not working.

You can use any of the disk benchmark programs that are found on the Web, to test disk performance with DisableDeleteNotify set to 0 or 48. Who knows? You might actually find a difference in performance. (I have not found any explanation of the value 48.)

Otherwise, the only thing left to do is to regularly check for new versions of the disk driver and firmware, to keep them up to date as much as possible. If TRIM is not functional at the moment, it will become functional sometime in the future.

To answer your other question: TRIM cannot affect non-SSD drives on the computer. It will be silently ignored by the disk driver or the disk firmware.

I did find also the article Enabling TRIM support in Windows 7 which details a method of finding if the firmware supports TRIM:

Download, install and run the Intel SSD Toolbox. If your drive is not an Intel SSD, the only option available will be "View Drive Information". Click that. Scroll down to Word 169 and look at the value for Bit 0 - Data Set Management Supported. if this is 1, you have TRIM. If 0, you don't.

The article How To check if SSD and TRIM have all windows 7 functions working? also says:

Generally, if you have the SSD hard drive, win7 would disable disk defragmentation, Superfetch, Prefetcher and ReadyBoost features. If you want to check their state, you can use the following steps.

Navigate to the following registry,

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters

If the superfetch and prefetch features are disabled, their registry value should be 0, please check if EnablePrefetcher and EnableSuperfetch are both set to 0.

It also says :

To check if the SSD has been properly detected by looking in Disk Defragmenter.

1. Open Disk Defragmenter
2. Click the Configure schedule button
3. Click the Select disks button

If the disk is missing from the list, then it has been detected as an SSD and will not be automatically defragmented.