• Updated 2023-07-12: Hello, Guest! Welcome back, and be sure to check out this follow-up post about our outage a week or so ago.

Actual capacity of 32GB SD cards


Well-known member
So, I'm working on something for my SCSI2SD to make it easier to work with following the same idea as what Andrew did with an exFAT SD card.

To deal with the varying "actual" capacity of SD cards my plan was originally to have a 29GB file that people can RAW-write to an SD card that will create a 29GB FAT32 formatted partition that contains the 48k "header" file and a set of volume/partition files that line up with where the SCSI2SD expects to find them, leaving the remaining part of the SD card blank to allow for variances in SD card sizes.

BUT, as part of my testing I found a 32GB SD card that only holds 28.9GBs. I was surprised by this.
So my question is how small do I need to go to be safe what I'm doing to work for anyone with a 32GB SD card? I'm thinking a 28.5GB partition should give plenty of room.

Note, I originally picked 29GB because I thought even if the SD card manufacturer used multiples of 1000 starting with bytes the result would still be 29.8GB in actual storage.... turns out that is not the case.