It can be booted from any disk that DOS recognizes. You just need to copy the files to the BOOTCFG subdirectory in the root directory, then run lowest.com and then run the default fourth stage boot loader ldr\4\patio.com, for my kernel (first stage is the boot sector, second stage is DOS, third stage is the lowest.com configurator and the fourth stage is patio.com and my kernel).
I only need to add support for FAT32 LBA and ATA disks as the minimum to load programs and files reliably, as I stated before. Currently it can only run external programs in a floppy.
I used it because it's the simplest mass storage device. I just need to read the FAT table to a cache in memory and scan short file names in the root directory. Otherwise I would need to use ATA commands, detect recognized partitions, probably add USB or SATA drivers, and then scan the FAT table without caching it all, it's simply too big to be kept at once. It's realistically too difficult for a starting system based on learning how to implement solutions to common personal needs first to make it immediately usable and still scalable with future additional features added basically as additional separate cases with increasing complexity. And configuration options typically passed at boot time, instead as commands driven by a kernel console that would always remain available no matter how advanced the system becomes, to tweak special low level options at run time.
And still the floppy is difficult enough to use, with all of its commands and the obligatory usage of ISA DMA. And I'm still figuring out how to detect read errors to abort loading a badly-read program binary code, or just let the system crash until I add exceptions and multitasking to isolate the task from the state of the kernel itself.
Here's a map of the current system, which shows clearly all of the features that the code implements at the end of its superficial functional chain: