Can I use the empty space on my bootable USB drives for storage?

Hi
Long story. But I suddenly find myself urgently needing some disk storage but without the chance to get hold of new hardware. I have several USB flash (SSD) drives which are either emergency/bootable disks for
1) Windows 10 disc image / create installation media or2) Macrium Reflect Rescue PE/ disk images for my computer's C: drive
...and which have a lot of free space on them. Can I store regular files on the empty space without damaging the functionality / bootability ? thanks

Win10 Home 64bit / Macrium Reflect Home v7.3.5758

If the flash drives were formatted FAT32 then the flash drives are likely using the maximum of 32 GB.

If this is the situation then consider creating multiple bootable partitions on one flash drive: Ventoy





Other options: How to Format USB Drives Larger Than 32GB With FAT32 on Windows

Hi
I already have the disks formatted as bootables. I just want to drag new files onto the unused space. It seems that those solutions involve prepping the drives before making the bootable (i.e. partitioning, using dedicated subfolders etc).

I'm asking whether it is safe to just add regular files to an already existing/fomatted drive
thanks

Typically you can use the remaining free space without problems.

Bree said:

As long as you don't overwrite an exiting file then yes, it's safe. Probably safest to make a new folder and put your files there, just to make sure you keep them well away from the required boot files.
Bear in mind that a bootable usb is almost certainly formatted as Fat32. There's an individual file size limit of 4GB for a Fat32 partition.
Also, a bootable Fat32 USB will be a maximum of 32GB. If the USB you used was larger than 32GB, then the rest of it will be unallocated space. You can safely create a second partition to use that space and, if you wish, format it as ExFAT or NTFS to get around the 4GB Fat32 filesize limit.

If a larger USB drive is used and 3rd party ware was used to convert/see a larger drive, say 64gb as fat32 would you still be limited to 4gb individual file/folder sizes on this drive?

Bree said:

Yes.

File Allocation Table - Wikipedia

So in essence the only real reason for keeping fat 32 is commercial, in as much practically every PC on the planet can utilize fat32, for example when purchasing a new external flash drive?