Think of the IPSW as the "master copy" of the operating system. When you restore your iPhone via iTunes (or Finder on modern Macs), the software downloads this file, unpacks it, and writes the data to your phone’s NAND storage.
Are you trying to or just update a legacy device for basic use? iphone 6 a1586 firmware
Because Apple no longer signs older firmware, you need archived copies. These cannot be installed on a stock device unless you have valid SHSH blobs and a compatible SEP. For archival or research purposes: Think of the IPSW as the "master copy"
Before downloading any software, it is vital to confirm that you are working with the correct hardware model. The iPhone 6 was released in two primary variants: Because Apple no longer signs older firmware, you
Why does this matter for firmware? Because Apple signs firmware based on the device’s hardware identifier. The A1586 uses the hardware identifier iPhone7,2 . When you download firmware, you must always look for the iPhone7,2 designation to ensure it matches your A1586.