So I have windows 7 working with AHCI support, Samsung telling me T.R.I.M is enabled. I use that as my control.
I want to dual boot. SSD is set, so I install windows 10 on a separate HDD and the only way to do that is to put the bios on IDE mode because im installing windows 10 on the hitachi. Now that all works.

Windows 10 took the OS selection over, so i boot back into windows 7 and make that my default. now i get the windows 7 OS selection.
Proceeded to try and get windows 7 to boot with my mobo in AHCI mode to no avail. (my thought was maybe i could plug the windows 10 HDD into a non-AHCI slot and it might work IDE, but booting refused.

SO my next thought was to partition the SDD 75GB and install win10 on the SSD and get me a drive a could wipe out of it, and then my SDD would dual boot both in AHCI. hours later, I've determined windows 10 does not play nicely with older stuff as it would not detect anything past the boot cycle with windows 10 anything remotely enabled.

Using a Rufus ISO to install , i have been doing this on this particular machine for years. Works fine. Windows 10 USB installation with NOT recognize my SSD at all . there's a 0mb (can't do absolutely anything) with partition.

so because i want to dual boot, i cannot use AHCI on my windows 7 OS for some reason with an IDE enabled copy of windows installed on another sata drive

Operating System
Windows 10 Professional (x64) Version 1803 (build 17134.81)
Install Language: English (United States)
System Locale: English (United States)
Installed: 5/24/2018 7:52:47 PM
Servicing Branch: Insider Preview
Boot Mode: BIOS (Secure Boot not supported)
System Model
Gateway DX4300
Enclosure Type: Desktop
Processor a
2.40 gigahertz AMD Phenom 9750 Quad-Core
512 kilobyte primary memory cache
2048 kilobyte secondary memory cache
2048 kilobyte tertiary memory cache
64-bit ready
Multi-core (4 total)
Not hyper-threaded
Main Circuit Board b
Board: Gateway RS780
Bus Clock: 200 megahertz
BIOS: American Megatrends Inc. P01-B1 03/06/2010
749.15 Gigabytes Usable Hard Drive Capacity
310.70 Gigabytes Hard Drive Free Space

Generic Mini SD Reader USB Device [Hard drive] -- drive 7
Generic USB CF Reader USB Device [Hard drive] -- drive 4
Generic USB MS Reader USB Device [Hard drive] -- drive 6
Generic USB SD Reader USB Device [Hard drive] -- drive 3
Generic USB xD/SM Reader USB Device [Hard drive] -- drive 5
Hitachi HTS545050A7E380 [Hard drive] (500.11 GB) -- drive 1, s/n TE854349C85GJR, rev GG2OA7A0, SMART Status: Healthy
Samsung SSD 840 Series [Hard drive] (250.06 GB) -- drive 0, s/n S14GNEBCB98589P, rev DXT0AB0Q, SMART Status: Healthy
SanDisk Cruzer Blade USB Device (7.90 GB) -- drive 2, s/n 20060266521644E1932F
Memory Modules c,d
7936 Megabytes Usable Installed Memory

Slot 'DIMM0' has 2048 MB (serial number 1E867396)
Slot 'DIMM1' has 2048 MB (serial number F6887396)
Slot 'DIMM2' has 2048 MB (serial number 535FA683)
Slot 'DIMM3' has 2048 MB (serial number 4B5FA683)
Local Drive Volumes
c: (NTFS on drive 1) * 80.67 GB 48.93 GB free
e: (NTFS on drive 1) 418.95 GB 126.82 GB free
f: (NTFS on drive 0) 249.53 GB 134.95 GB free