DISC logical format

■Summary

The CD-ROM area and CD-ROM XA area consist of a system area and a data area.
At the beginning of the data area, a set of volume descriptors, directories, and path tables are recorded to describe the volume/file structure of the disk. (Figure 3.1)
The system area, volume descriptor set, root directory, and path table must be recorded on the Mode1 track.

Figure 3.1 Overview of CD-ROM area and CD-ROM XA area

■Volume/file structure

●Summary

The volume/file structure complies with ISO9660.
Information has been added to the system area of the directory record.

●Symbols representing data types

The following abbreviations are used to represent volume/file structures.

Table 3.1 Abbreviations representing data types

Abbreviation	Model name	explanation
N	Numeric Value	8 bit binary number
N.L.	Least Significant Byte First	LSBF notation 16/32 bit binary number Example) Recorded as hexadecimal number 1234 → 34 12
N.M.	Most Significant Byte First	MSBF notation 16/32 bit binary number Example) Hexadecimal number 1234 → recorded as 12 34
N.B.	Both-type orders	LSBF notation + MSBF notation Example) Hexadecimal number 1234→34 12 12 34 is recorded
N.D.	Any digit from ZERO-NINE	Numeric value in decimal notation
A	A-characters	ASCII string (20-22/25-3F/41-5A/5F)
D	D-characters	Directory string (30-3F/41-5A/5F)
DS	D-characters, SEPARATOR1, SEPARATOR2	D-characters+'.;'(2E/3B)
D.E.	Directory Entry	directory entry format
A1	A1-characters	A-characters+Kanji
D1	D1-characters	D-characters+Kanji
D1S	D1-characters,SEPARATOR1, SEPARATOR2	D1-characters+'.;'(2E/3B)
00	Zero fill	Fill unused and reserved areas with (00)

Figure 3.2 File management data structure in CD-ROM (ISO9660)

• volume descriptor
  Arranged from the beginning of the data area. Fixed length depending on type.

• path table
  A collection of path table records. The size and address of the path table are recorded in the volume descriptor.

• path table record
  Supports one directory (root, sub). The position of the record becomes the directory number. (1 to n) Directory information is written in the directory block.

• directory block
  A collection of directory records. Treats a directory block as one file. (Directory file) The size of the directory block is recorded in the file size of the directory record at the beginning of the block. (size of own directory file)

• directory record
  Supports one file (including directory).

■Volume Descriptor Set

A volume descriptor set is a collection of volume descriptors recorded in consecutive sectors starting from logical sector number 16 (FAD=166).
There are five types of volume descriptors: Of these, volume partition descriptors are not used.

Figure 3.3 Volume descriptor

●Boot record

Table 3.2 Boot record structure

Byte position	mold	Field name	explanation
1 2~6 7 8～39 40～71 71～2048	N N A A	Volume Descriptor Type Standard Identifier Volume Descriptor Version Boot System Identifier Boot Identifier Boot System Use	volume descriptor type Standard identifier 'CD001' Volume descriptor version number boot system identifier boot identifier Not stipulated

In a normal GAME-CD, one sector each of the basic volume descriptor and volume descriptor set terminator is recorded. These two sectors must be recorded.

Be sure to fully understand how to use the secondary volume descriptor and boot record before using them.

●Primary Volume Descriptor

A volume descriptor set contains one basic volume descriptor. The basic volume descriptor describes volume attributes, the location of the root directory, the location of path tables, etc.
Table 3.3 shows details of the basic volume descriptor.

Table 3.3 Basic volume descriptor structure

Byte position	mold	Field name	explanation
1 2~6 7 8 9～40 41～72 73～80 81〜88 89〜120 121〜124 125〜128 129〜132 133〜140 141〜144 145〜148 149〜152 153〜156 157〜190 191〜318 319〜446 447〜574 575〜702 703〜739 740〜776 777〜813 814〜830 831〜847 848〜864 865〜881 882 883 884～1395 1396~2048	N N 00 A D 00 N.B. 00 N.B. N.B. N.B. N.B. N.L. N.L. N.M. N.M. D.E. D A A A DS DS DS N.D. N.D. N.D. N.D. N 00	Volume Descriptor Type Standard Identifier Volume Descriptor Version Unused Field System Identifier Volume Identifier Unused Field Volume Space Size Unused Field Volume Set Size Volume Sequence Number Logical block size Path Table Size Location of Occurrence of Type L Path Table Location of Optional Occurrence of Type L Path Table Location of Occurrence of Type M Path Table Location of Optional Occurrence of Type M Path Table Directory Record for Root Directory Volume Set Identifier Publisher Identifier Data Preparer Identifier Application Identifier Copyright File Identifier Abstract File Identifier Bibliographic File Identifier Volume Creation Date and Time Volume Modification Date and Time Volume Expiration Date and Time Volume Effective Date and Time File Structure Version Reserved for future standardization Application Use Reserved for future standardization	Volume descriptor type = 01 Standard identifier 'CD001' Volume descriptor version number unused Systems using LSN 0-15 volume name unused Number of sectors in the entire volume unused Number of volumes during multi-volume = 1 Volume serial number during multi-volume Logical block length Number of bytes in entire path table Path table position in LSBF notation spare Path table location in MSBF notation spare directory record for root directory Overall name during multi-volume publisher identifier Data editor identifier Identification of how data is used Copyright file name Abstract (abstract) file name Bibliographic file name Creation date and time Update date and time Expiration date, time Effective date and time File structure version number Reserved for future standardization Compliant with CD-ROM XA standard Reserved for future standardization

The CD-ROM XA standard specifies the following areas as disc labels.

Table 3.4 Disc label on CD-ROM XA

Byte position	mold	Field name	explanation
1025~1032 1033~1034 1035~1042 1043~1050	D 00	Identifying Signature CD-ROM XA Flags Startup Directory Reserved	'CD-XA001' reserved area startup directory name reserved area

●Supplementary Volume Descriptor

A volume descriptor set includes any number of secondary volume descriptors. The secondary volume descriptor describes volume attributes, root directory location, path table group location, etc.
When Japanese characters are used in identifiers such as volume names and publisher identifiers, they are recorded in the secondary volume descriptor. Table 3.5 shows details of the secondary volume descriptor.

Table 3.5 Structure of secondary volume descriptor

Byte position	mold	Field name	explanation
1 2~6 7 8 9～40 41～72 73～80 81〜88 89〜120 121〜124 125〜128 129〜132 133〜140 141〜144 145〜148 149〜152 153〜156 157〜190 191〜318 319〜446 447〜574 575〜702 703〜739 740〜776 777〜813 814〜830 831〜847 848〜864 865〜881 882 883 884～1395 1396~2048	N N A1 D1 00 N.B. 00 N.B. N.B. N.B. N.B. N.L. N.L. N.M. N.M. D.E. D1 A1 A1 A1 D1S D1S D1S N.D. N.D. N.D. N.D. N 00	Volume Descriptor Type Standard Identifier Volume Descriptor Version Volume Flag System Identifier Volume Identifier Unused Field Volume Space Size Unused Field Volume Set Size Volume Sequence Number Logical block size Path Table Size Location of Occurrence of Type L Path Table Location of Optional Occurrence of Type L Path Table Location of Occurrence of Type M Path Table Location of Optional Occurrence of Type M Path Table Directory Record for Root Directory Volume Set Identifier Publisher Identifier Data Preparer Identifier Application Identifier Copyright File Identifier Abstract File Identifier Bibliographic File Identifier Volume Creation Date and Time Volume Modification Date and Time Volume Expiration Date and Time Volume Effective Date and Time File Structure Version Reserved for future standardization Application Use Reserved for future standardization	volume descriptor type Standard identifier 'CD001' Volume descriptor version number volume flag Systems using LSN 0-15 volume name unused Number of sectors in the entire volume unused Number of volumes during multi-volume = 1 Volume serial number during multi-volume Logical block length Number of bytes in entire path table Path table position in LSBF notation spare Path table location in MSBF notation spare directory record for root directory Overall name during multi-volume publisher identifier Data editor identifier Identification of how data is used Copyright file name Abstract (abstract) file name Bibliographic file name Creation date and time Update date and time Expiration date, time Effective date and time File structure version number Reserved for future standardization Not stipulated Reserved for future standardization

■Directory

A directory is recorded as a single file consisting of multiple directory records. Each directory record is uniquely identified within the same directory by its file identification.
File identification represents a file name or directory name and is stored in the following format.

                          Up to 8 characters 
                          |          Up to 3 characters, can be omitted 
                          |          |           Number from 1 to 32767 (Always set to 1)
                          ↓          ↓           ↓ 
File identification → file name. Extension; version number 
                    ↑          ↑          ↑ 
                    |          |          Delimiter 2 “Semicolon” 
                    |          Number of delimiters: 1 “period” 
                    |          
               Directory name: Up to 8 characters 
               (The root directory is 1 byte 00H)　

Table 3.6 Directory record

Byte position	mold	Field name	explanation
1 2 3-10 11-18 19-25 26 27 28 29-32 33 34~ (33+LEN_FI) 34+LEN_FI	N N N.B. N.B. N N N N.B. N D1S 00	Length of Directory Record Extended Attribute Record Length Location of Extent Data length Recording Date and Time File Flags File unit size Interleave Gap Size Volume Sequence Number Length of File Identifier File Identifier Padding Field System use	directory record length Extended attribute record length Extent location (LSN) Data length Recording date/time file flag file unit size Interleaving gap size volume sequence number File identification length file identification ・ file name. Extension; version number ・ Directory name embedded System information

●Format of recording date and time

Table 3.7 Recording date/time format

Byte position	mold	Field name	explanation
1 2 3 4 5 6 7	N N N N N N N	Number of years since 1900 Month of the year from 1 to 12 Day of the month from 1 to 31 Hour of the day from 0 to 23 Minute of the hour from 0 to 59 Second of the minute from 0 to 59 Offset from Greenwich Mean Time in number of 15 min intervals from-48 (West) to +52 (East)	Years since 1900 Month Day Time minutes seconds Difference from Greenwich Mean Time -48 (west) to +52 (east) in 15 minute increments

●File flag

Table 3.8 File flags

bit position	Field name	explanation
0 1 2 3 4 5 6 7	Existence Directory Associated File Record Protection Reserved Reserved Multi-Extent	invisible file directory file Related files (=0) Extended attribute record structure file Protected file (=0) Multiple extent file (=0)

●File identification

The file name or directory name is stored according to the value of the directory bit (bit 1) of the file flag.
Directory bit = 0: Specify identification information for the file.

Table 3.9 File identification

Directory bit value	format	explanation
0	file name. Extension; version number 《Example》aaaaaaaa.bbb;1 xxxxxxx;1	File name: Up to 8 characters Extension: Up to 3 characters (optional) Version number: Always 1
1	Directory name	Directory name: Up to 8 characters The root directory is 1 byte 00H

If the file identification length is an even number, 1 byte (00H) is inserted.

●System information

The following extensions will be made to the ISO9660 standard.

Table 3.10 Information for the system

Byte position	mold	Field name	explanation
14 5～6 7 8 9 10-14	N.M. N 00	Owner ID Attributes Signature byte 1 Signature byte 2 File Number Reserved	Owner group ID, owner ID attribute bit 'X'($58) 'A'($41) file number reserved area

●Attribute bit

Table 3.11 Attribute bits

bit position	Field name	explanation
0 1 2 3 Four Five 6 7 8 9 Ten 11 12 13 14 15	Owner Read Reserved Owner execute Reserved Group read Reserved Group execution Reserved World read Reserved World execute File contains Form 1 sectors File contains Form 2 sectors File contains interleaved sector CD-DA file Directory	Form contains 1 sector Contains Form 2 sectors Contains interleaved sectors CD-DA file directory file

■Pass table

A path table record is recorded for each directory in the directory hierarchy. Path table records are numbered starting with 1, with the first record indicating the root directory.
The details of the path table record are shown below.

Table 3.12 Path table record

Byte position	mold	Field name	explanation
1 2 3-6 7~8 9～ (8+LEN_DI) 9+LEN_DI	N N N N D1 00	Length of Directory Identifier Extended Attribute Record Length Location of Extent Parent Directory Number Directory Identifier Padding Field	Directory name length Extended attribute record length LSN at the beginning of the extent Parent directory entry number Directory name Only if the directory name is an odd number

■User file

User files are placed in the data area.
One file is not necessarily placed consecutively, but is generally placed interleaved. Mode2 sectors are a mixture of Form1 and Form2, but each sector is converted to a file size of 2048 bytes.
For convenience, Mode1 sectors are formally treated as Form1 sectors with a subheader of 0.
Form2 sector data must be in units of 2324 bytes, and fractional bytes are not allowed.

■Others

●Directory structure

GAME-CD also supports subdirectory structures.

●Multi volume

Not supported.

●Multi-session

Not supported.