I have wiped an old imac as per advice before selling
The drive is 1 TB yet when I try and download High Sierra it says not enough disk space?
Any ideas what I am doing wrong?
iMac 27″
Did you select the whole physical drive (or Fusion Drive if applicable) when you erased this Mac? If this Mac was running macOS 10.15+, then they use multiple APFS volumes. Unless you erase the complete Volume Group, you may have only erased the "Macintosh HD" volume which only contains the macOS system files....your user data may still be on the other "Macintosh HD - Data" volume. Within Disk Utility you may need to click "View" and select "Show All Devices" before the physical drives appear on the left pane of Disk Utility.
If your Mac uses a Fusion Drive setup, then just select the "Fusion Drive" item on the left pane to erase.
Here is an Apple article showing how to erase a disk...it mentions the "Volume Group", but it is hard to say whether macOS 10.13 High Sierra will know anything about it. This method in that Apple article is safe for Apple Silicon Macs as well and Fusion Drives.
Here is an Apple article for how to prepare a Mac computer for sale:
What to do before you sell, give away, or trade in your Mac - Apple Support
FYI, if your Mac uses a hard drive (or Fusion Drive) as opposed to just an SSD, then I highly recommend you either use the secure erase feature of Disk Utility to write zeroes to the hard drive, or a simpler option may be to first enable Filevault and let Filevault finish encrypting the hard drive before you try to erase the hard drive. Encrypting the drive or writing a single pass of zeroes to it will take a long time depending on the size & speed of the hard drive, and also the health of the hard drive (could easily take a day even for a 1TB hard drive). If your Mac uses a hard drive, then the simple erase as mentioned in the Apple documentation will still have your personal data accessible if someone tried using a data recovery app on the hard drive. If the Mac only uses an SSD, then a simple erase is sufficient due to how SSDs work.
Did you select the whole physical drive (or Fusion Drive if applicable) when you erased this Mac? If this Mac was running macOS 10.15+, then they use multiple APFS volumes. Unless you erase the complete Volume Group, you may have only erased the "Macintosh HD" volume which only contains the macOS system files....your user data may still be on the other "Macintosh HD - Data" volume. Within Disk Utility you may need to click "View" and select "Show All Devices" before the physical drives appear on the left pane of Disk Utility.
If your Mac uses a Fusion Drive setup, then just select the "Fusion Drive" item on the left pane to erase.
Here is an Apple article showing how to erase a disk...it mentions the "Volume Group", but it is hard to say whether macOS 10.13 High Sierra will know anything about it. This method in that Apple article is safe for Apple Silicon Macs as well and Fusion Drives.
Here is an Apple article for how to prepare a Mac computer for sale:
What to do before you sell, give away, or trade in your Mac - Apple Support
FYI, if your Mac uses a hard drive (or Fusion Drive) as opposed to just an SSD, then I highly recommend you either use the secure erase feature of Disk Utility to write zeroes to the hard drive, or a simpler option may be to first enable Filevault and let Filevault finish encrypting the hard drive before you try to erase the hard drive. Encrypting the drive or writing a single pass of zeroes to it will take a long time depending on the size & speed of the hard drive, and also the health of the hard drive (could easily take a day even for a 1TB hard drive). If your Mac uses a hard drive, then the simple erase as mentioned in the Apple documentation will still have your personal data accessible if someone tried using a data recovery app on the hard drive. If the Mac only uses an SSD, then a simple erase is sufficient due to how SSDs work.
What format is the drive?
my disk is empty why does it say I don't have enough space to install OS?
