The startup disk cannot be partitioned or restored to a single partition - Tried Everything - Version 2

You should be able to install W7 on your 2012 iMac. Your iMac allows only a legacy BIOS installation of Windows (7/8.1/10), which uses a Hybrid MBR. Due to limitations of a MBR,

• your Windows partition must be >1TB, or
• must be 'sandwiched' between two chunks and should start within the first 2TB of the disk. This requires a CS volume, if you want the chunks to behave like a contiguous macOS JHFS+ volume. Since you do not have a SSD, some of the benefits do not apply.

You can use

• a USB2 flash drive build by BC Assistant for the Windows installer, or,
• a DVD in your built-in Optical drive and the USB2 flash drive used to store the BC drivers.

A manual build of a USB2 flash drive Installer is also possible, using Build your own Windows 10 Bootcamp USB Installer (this is valid for W7/W8.1 as well). This replaces the first two tasks - Create and Download - in BCA.

Partitioning can be done using Disk Utility, as long as you use a tool (like GPT Fdisk) to create a matching MBR.

Kappy wrote:

I thought it was dropped earlier than his model. He will need the BC support: Boot Camp Support Software 5.1.5621 for 64-bit or Boot Camp Support Software 4.0.4326 for 32-bit. Also, for reference: Boot Camp- System requirements for Microsoft Windows operating systems, including mine.

W7 is supported on Macs up to 2014 models. 2015 and later models dropped CSM-BIOS and effectively dropped support for W7.

Kappy wrote:

BTW, a Windows partition greater than 1TB? Don't you mean less than?

The layout on 3TB disks (including Fusion equivalents) is typically

• for less than 1TB Windows partition - macOS + Windows + macOS, with the two macOS parts in a CS, or,
• for greater than 1TB Windows partition - macOS + Windows

This allows 32-bit numbers used in a MBR to accommodate up to 2TB Windows partitions in BIOS mode. EFI has no such restriction, but requires W8.1/W10. EFI in W7 is very painful.

Apple never went to 4TB disks or equivalent Fusion drives.

I thought it was dropped earlier than his model. He will need the BC support: Boot Camp Support Software 5.1.5621 for 64-bit or Boot Camp Support Software 4.0.4326 for 32-bit. Also, for reference: Boot Camp- System requirements for Microsoft Windows operating systems, including mine.

BTW, a Windows partition greater than 1TB? Don't you mean less than?

You don't have a cs managed drive. Use diskutil list. How are attempting to partition the drive? The drive appears to be a single partition. Nothing to be restored. Partition the drive using Boot Camp Assistant. You should install Win 10, not 7 which is no longer supported.

I was not familiar with these requirements on 3TB drives. 1TB is a pretty large allocation for Windows at 1/3 of the drive's total capacity. Were it me I think I would stick to VM like Parallels. Less fuss and no muss. 😀

Kappy - his machine should allow W7, irrespective of the version of macOS.

What is the first prompt you cannot get past? A screenshot would be very helpful. Use Utilities -> Grab.

Did you run a SMC and NVRAM Reset after the disk was replaced/upgraded? As a test, try and create a FAT32 partition on the disk via Disk Utility.

Does BCA allow you to create a partition after you removed the one created by DU?

Do you have a Time Machine backup of macOS? We should manually partition the disk and try to install Windows using a manually built W7 USB Installer.