[Coco] OS-9 / NitrOS9 floppy disk directory layout.

[coco at jechar.ca]

Thanks this is good one more question more specific this time, if you 
have a 1.5 MB virtual OS9 disk and it is bootable are the boot track and 
OS9Boot file all within the first 160K ?

On 2022-06-12 13:23, L. Curtis Boyle wrote:
> Where it will be will depend on the size of the disk (how many tracks,
> sides and sectors per track). LSN0 (sector 0) contains this
> information so that you can figure that out no matter which size of
> disk you are dealing with. It also has the sector number that the root
> directory starts at.
> Floppy drives and hard drives use the same format; logical sector
> numbers are all 24 bit numbers. On real large drives you may have to
> deal with clusters as well (multiple sectors counting as a single
> “block” as far as free space, etc are concerned. You are correct that
> each directory entry is 32 bytes; 29 for the filename, and a 3 byte
> sector number that points to a description of the file (or
> sub-directory, they use the same structures). The file description
> sector has file attributes, segment lists, etc and points to the
> actual data in a file/directory. Each segment entry is 5 bytes; 3
> bytes for sector number each segment starts at, and then 2 bytes for
> how big that segment is. On a real Coco these segments max out at 2048
> (due to how RBF internally uses memory to buffer things), but since
> you have up to 48 segments per file, that’s still pretty large.
> Maximum number of files per directory is the same for all directories,
> root or otherwise, and is based on the segment lists above. 8 files
> per sector, 2048 sectors per segment, 48 segments (multiply that all
> together) means over 768,000 files. There are practical limitations
> though, so would never get that high in real life. (Some are - disk
> fragmentation from creating deleting files eventually means that you
> can’t make full sized segments. The OS finding files in a directory
> even with just a few thousand files would start to slow things down; I
> can’t imagine what performance would be like with 10’s or 100’s of
> thousands of files. So make subdirectories way before you start making
> directories that big).
> 
> Hopefully I didn’t go to overboard explaining this, but I think I
> answered your questions. :-)
> 
> Sent from my iPhone
> 
>> On Jun 12, 2022, at 11:04 AM, coco at jechar.ca wrote:
>> 
>> All
>> 
>> I wanted to know where the directory for an OS-9 floppy is located, I 
>> think it takes 32 Bytes per file entry could someone confirm this. 
>> Also I was wondering if it is all on contiguous sectors and is there a 
>> maximum number of files in the root directory or sub directory. Is it 
>> identical to the OS-9 hard drive directory format or does that follow 
>> different rules.
>> 
>> Thanks Chatlie
>> 
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> https://pairlist5.pair.net/mailman/listinfo/coco
>>