UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Gemini 80-Bus System

john_newcombe · 16th May 2019, 8:18 am

I am rather confused about the .img format as I found this on Wikipedia...

The file size of a raw disk image is always a multiple of the sector size. For floppy disks and hard drives this size is typically 512 bytes (but other sizes such as 128 and 1024 exist). More precisely, the file size of a raw disk image of a magnetic disk corresponds to:

Cylinders × Heads × (Sectors per track) × (Sector size)
E.g. for 80 cylinders (tracks) and 2 heads (sides) with 18 sectors per track:

80 × 2 × 18 × 512 = 1,474,560 bytes or 1440 KB

This suggests that IAMs, CRCs and gap bytes are not included in an .img file, fascinating. I have written to Keir Fraser the author of FlashFloppy in the hope that he can shed some light on the process of adding Gemini to the supported disk types.

16th May 2019, 8:18 am	#48
john_newcombe Hexode Join Date: Apr 2019 Location: Skipton, North Yorkshire, UK. Posts: 252	Re: Gemini 80-Bus System I am rather confused about the .img format as I found this on Wikipedia... The file size of a raw disk image is always a multiple of the sector size. For floppy disks and hard drives this size is typically 512 bytes (but other sizes such as 128 and 1024 exist). More precisely, the file size of a raw disk image of a magnetic disk corresponds to: Cylinders × Heads × (Sectors per track) × (Sector size) E.g. for 80 cylinders (tracks) and 2 heads (sides) with 18 sectors per track: 80 × 2 × 18 × 512 = 1,474,560 bytes or 1440 KB This suggests that IAMs, CRCs and gap bytes are not included in an .img file, fascinating. I have written to Keir Fraser the author of FlashFloppy in the hope that he can shed some light on the process of adding Gemini to the supported disk types.