TRSDOS (and compatables, e.g. LDOS, NEWDOS) Reference - www.fileden.com/files/2008/7/6/1990698/manuals-NewDOS-80_v2.0_manual.pdf pages 99-101 (previous location - www.classic-computers.org.nz/system-80/software-manuals/manuals-NewDOS-80_v2.0_manual.pdf ) sectors 2-9 of the directory track (17) contain File Primary Directory Entries, which are 32 bytes made up of:

 byte $00:
     bit 7 : 0 = FPDE, 1 = FXDE
     bit 6 : 1 means a SYSTEM file
     bit 5 : undefined
     bit 4 : 1 = in use, 0 = entry empty
     bit 3 : 1 = file is hidden
     bit 2 - 0 : access level code
 byte $01:
     bit 7 : 0 =  file may be allocated more space when necessary
     bit 6 : 0 =  any excess space past the EOF may be deallocated
     bit 5 : 1 = at least one sector of the file has been written to since this bit was last reset
     bit 4 - 0 : undefined
 byte $02: undefined
 byte $03: low order byte of the file's EOF (position of the EOF within the EOF sector)
 byte $04: logical record length
 byte $05-$0C : file name (right padded with blanks)
 byte $0D-$0F: file extension (right padded with blanks)
 byte $10-$11 : encode of the upate password
 byte $12-$13 : encode of the access password
 byte $14 : middle order byte of the EOF
 byte $15 : high order byte of the EOF
 byte $16 - $1F : 5 pairs of extent elements, each pair made up of:
     byte $00 : if $FF, then end of extent elements for this file. if $FE, then next byte contains the DEC for the first (or next) FXDE assigned to this file.
                     any other value ($00-$FD) equals the number of the diskette's lump in which the area starts.
     byte $01  : bits 7-5 = number of granules (0-7) from the start of the lump to the start of the area
                   : bits 4- 0 = number less one of contiguous granules assigned to this area.

 when a file has more than 4 space areas assigned, the additional extent elements are contained in FXDE's assigned to the file.
 the format of a FXDE is:
 byte $00: bits 7 and 4 are both 1 to indicate this entry is a FXDE, all other bits are 0
 bute $01: the DEC for the previous FPDE or FXDE of this file. This is a backward chain. the previous entry's byte $1E will be $FD, and it's byte $1F will contain the DEC of this FXDE

 the EOF value (bytes $03, $14, $15) is decoded as:
   if low order byte ($03) = 0, then EOF is in RBA format
   if low order byte ($03) != 0, then EOF in the FPDE is equal to the RBA value plus 256 (the value in the high two bytes is incremented by 1)

 RBA = Relative Byte Address : a method of addressing where addressing starts at 0 rather than 1

 DEC = Directory Entry Code  - a one byte code used to specify a particular FDE. Format is rrrssss, where sssss+2 = the relative
 number within the directory of the sector containing the FDE, and rrr times $20 = the relative byte address within the sector
 of the FDE.