pwu@uwmacc.UUCP (02/09/87)
Can someone tell me which document describes the disk layout on
floppy disks (i.e. structures of directories, how file sectors
are linked together, etc)? Thanks.
Also, what's the present interleave factor on floppy? If it's not
optimal is it possible to change it?
peter
/*
** ARPA: pwu@unix.macc.wisc.edu BITNET: WU at WISVMACC
** UUCP: {seismo|harvard|topaz|caip|ll-xn| <-+
** allegra|akgua|ucbvax|bellcore|ihnp4}!uwvax!uwmacc!pwu |
** |
** Uuhosts on this line may have faster delivery time. --------+
*/cmcmanis@sun.UUCP (02/09/87)
In article <1037@uwmacc.UUCP>, pwu@uwmacc.UUCP (Peter Wu) writes: > Can someone tell me which document describes the disk layout on > floppy disks (i.e. structures of directories, how file sectors > are linked together, etc)? Thanks. Yup, it's the AmigaDOS Technical Reference manual. This is part of the Bantam Book, in the developer set it is a separate manual. Much can be gleaned by running disked while reading this manual. Note: Disked is also documented in there. > Also, what's the present interleave factor on floppy? If it's not > optimal is it possible to change it? > peter I think what you are really asking is "Is it possible to speed up the floppies?" But to answer your original question, there is no interleave factor since the trackdisk.device reads floppies a full track at a time. -- --Chuck McManis uucp: {anywhere}!sun!cmcmanis BIX: cmcmanis ARPAnet: cmcmanis@sun.com These opinions are my own and no one elses, but you knew that didn't you.
daveh@cbmvax.UUCP (02/10/87)
> Can someone tell me which document describes the disk layout on > floppy disks (i.e. structures of directories, how file sectors > are linked together, etc)? Thanks. > > Also, what's the present interleave factor on floppy? If it's not > optimal is it possible to change it? > > peter The document I've used in the past is the AmigaDOS Technical Reference Manual, from the original "Phonebook" collection of Amiga reference books. I believe the contents of this book are available in the Addison Wesley bookstore series, probably as part of the AmigaDOS User/Reference Manual (whatever they call it; the one that describes AmigaDOS, the CLI, etc.). The book contains information on the basic disk layout. Essentially, each floppy (or other device with a file structure) is organized as a logical sequence of 512 byte blocks. The floppy has around 1760 of these blocks. Blocks have various types. A ROOT block is a one-per disk item, found at block 880 on the floppy. This contains the hash table for the disk's root directory, plus the block allocation map for the disk. A related type is a root extension, which extends the block allocation map for large devices. Next is the user directory block. Each of these contains its own hash table for what's contained within it (in either case, the hash table is made up of 72 longword pointers, representing disk block locations). Files all start with a file header. The file header contains pointers to each block in the file, the file name, size, a pointer to the first block in a file, and a pointer back to the parent directory. Also avaiable is an extension pointer, which points to a file extension block, which will contain another set of block pointers, used for large files. Thus, a file header and its extension blocks contain pointers to each 512 byte block in the file. Each of the blocks actually making up the file is a data block. Data blocks have pointers to the next block in the sequence, the file header, some other bookkeeping stuff, and 488 bytes of data. Due to the random links available in file headers and the serial links available in data blocks, most or all of any file under AmigaDOS can be recovered independently of any other file or directory. You could clobber every directory entry on a disk and still get back every file, undamaged. As for interleave factor, there isn't any. All floppy read/writes are done by the Paula chip as full track reads/writes; never are individual sectors addressed by the hardware. -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dave Haynie {caip,ihnp4,allegra,seismo}!cbmvax!daveh "You can keep my things, they've come to take me home" -Peter Gabriel ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~