The CP/M 3.1 directory has four types of entry:
| Files | Disc label | Date stamps | Password control |
0U F1 F2 F3 F4 F5 F6 F7 F8 T1 T2 T3 EX S1 S2 RC .FILENAMETYP....
AL AL AL AL AL AL AL AL AL AL AL AL AL AL AL AL ................
0U = User number. 0-15. The user number allows multiple files of the same name
to coexist on the disc.
User number = 0E5h => File deleted
Fn - filename
Tn - filetype. The characters used for these are 7-bit ASCII.
The top bit of T1 (often referred to as T1') is set if the file is
read-only.
T2' is set if the file is a system file (this corresponds to "hidden" on
other systems). System files with user number 0 can be read from any user
number.
T3' is set if the file has been backed up.
EX = Extent counter, low byte - takes values from 0-31
S2 = Extent counter, high byte.
An extent is the portion of a file controlled by one directory entry.
If a file takes up more blocks than can be listed in one directory entry,
it is given multiple entries, distinguished by their EX and S2 bytes. The
formula is: Entry number = ((32*S2)+EX) / (exm+1) where exm is the
extent mask value from the Disc Parameter Block.
S1 - Last Record Byte Count
RC - Number of records (1 record=128 bytes) used in this extent, low byte.
The total number of records used in this extent is
(EX & exm) * 128 + RC
If RC is 80h, this extent is full and there may be another one on the disc.
File lengths are optionally saved exactly (using the S1 byte) but this
system is hardly ever used.
AL - Allocation. Each AL is the number of a block on the disc. If an AL
number is zero, that section of the file has no storage allocated to it
(ie it does not exist). For example, a 3k file might have allocation
5,6,8,0,0.... - the first 1k is in block 5, the second in block 6, the
third in block 8.
AL numbers can either be 8-bit (if there are fewer than 256 blocks on the
disc) or 16-bit (stored low byte first).
20 F1 F2 F3 F4 F5 F6 F7 F8 T1 T2 T3 LB PB RR RR LABENAMETYP....
P1 P2 P3 P4 P5 P6 P7 P8 D1 D1 D1 D1 D2 D2 D2 D2 ................
20h - Characteristic number of a disc label
F1-F8, T1-T3 - Label name, 7-bit ASCII
LB - Label byte. Bit 0 set => Label exists
Bit 4 set => Time stamp on create --+
Bit 5 set => Time stamp on update +--These 2 are mutually
Bit 6 set => Time stamp on access --+ exclusive
Bit 7 set => Password protection enabled
PB - Used to decode the label password
RR - Reserved, set to zero.
P1-P8 - password, rather feebly encrypted.
D1 - Label create datestamp
D2 - Label update datestamp
21 D1 D1 D1 D1 D2 D2 D2 D2 M1 00 D3 D3 D3 D3 D4 !............... D4 D4 D4 M2 00 D5 D5 D5 D5 D6 D6 D6 D6 M3 00 00 ................ 21h - Characteristic number of a date stamp. D1 - File 1 create OR access date D2 - File 1 update date D3 - File 2 create OR access date D4 - File 2 update date D5 - File 3 create OR access date D6 - File 3 update date M1 - File 1 password mode M2 - File 2 password mode M3 - File 3 password mode 00 - Reserved. The format of a date stamp is: DW day ;Julian day number, stored low byte first. ;Day 1 = 1 Jan 1978. DB hour ;BCD hour, eg 13h => 13:xx DB min ;BCD minute
1U F1 F2 F3 F4 F5 F6 F7 F8 T1 T2 T3 PM PB RR RR .FILENAMETYP....
P1 P2 P3 P4 P5 P6 P7 P8 RR RR RR RR RR RR RR RR ................
1U = 16+User number (ie 16-31). The user number will be the number of
the file to which the password belongs.
F1-F8 - Filename of the file to which the password belongs
T1-T3 - Filetype of the file to which the password belongs
PM - Password mode byte
Bit 7 set => Password required to read from file
Bit 6 set => Password required to write to file
Bit 5 set => Password required to delete file
PB - Used to decode the password
P1-P8 - The password, rather feebly encrypted.
RR - Reserved, set to 0.