DISC logical format

■ Overview

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, the volume descriptor set, directory, and path table for describing the volume / file structure of the disk are recorded. (Fig. 3.1)
Be sure to record the system area, volume descriptor set, root directory, and path table on the Mode1 track.

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

■ Volume / file structure

● Overview

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

● Abbreviation for data type

Use the following abbreviations to describe the volume / file structure.

Table 3.1 Abbreviations for data types

Abbreviation	Model name	explanation
N	Numeric Value	8-bit binary number
NL	Least Significant Byte First	LSBF notation 16/32 bit binary Numerical value Example) Hexadecimal number 1234 → 34 12 is recorded.
NM	MostSignificant Byte First	MSBF notation 16/32 bit binary Numerical value Example) Hexadecimal number 1234 → 12 34 is recorded.
NB	Both-type orders	LSBF notation + MSBF notation example) Hexadecimal number 1234 → 34 12 12 34 is recorded
ND	Any digit from ZERO-NINE	Number in decimal notation
A	A-characters	ASCII character string (20-22 / 25-3F / 41-5A / 5F)
D	D-characters	Directory character string (30-3F / 41-5A / 5F)
DS	D-characters, SEPARATOR1, SEPARATOR2	D-characters +'.;' (2E / 3B)
DE	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, reserved area, etc. with (00)

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

• It is placed from the beginning of the volume descriptor data area. Fixed length depending on the type.

• Pathtable A collection of pathtable records. Record the size and address of the path table in the volume descriptor.

• Path table record Corresponds to one directory (root, sub). The position of the record is the directory number. (1 to n) Directory information is described in the directory block.

• Directory block A collection of directory records. Consider a directory block as a 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 my directory file)

• Directory record Corresponds to one file (including directory).

■ Volume Descriptor Set

A volume descriptor set is a collection of volume descriptors recorded in consecutive sectors from logical sector number 16 (FAD = 166).
There are five types of volume descriptors: Of these, the volume partition descriptor is 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 specified

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

Make sure you understand how to use the secondary volume descriptor and boot record before using it.

● Primary Volume Descriptor

The volume descriptor set contains one base volume descriptor. The basic volume descriptor describes the volume attributes, the location of the root directory, the location of the path table group, and so on.
The details of the basic volume descriptor are shown in Table 3.3.

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 NB 00 NB NB NB NB NL NL NM NM DE D A A A DS DS DS ND ND ND ND 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 Occurence of Type L Path Table Location of Optional Occurence of Type L Path Table Location of Occurence of Type M Path Table Location of Optional Occurence 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 unused System volume name that uses LSN 0 to 15 Number of sectors in the entire unused volume Number of volumes in unused multi-volume = 1 Volume serial number at the time of multi-volume Logical block length Number of bytes in the entire path table Path table position in LSBF notation Reserve Path table position in MSBF notation Reserve Directory record of root directory Overall name during multi-volume Publisher identifier Data editor identifier Identification of data usage Copyright File name Abstract (summary) File name Bibliographic file name Creation date, time update date, time expiration date, time effective Date, time File structure Version number Reserved for future standardization Compliant with CD-ROM XA standard Reserved for future standardization

The following areas are defined as disc labels in the CD-ROM XA standard.

Table 3.4 Disc Labels 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

The volume descriptor set contains any number of subvolume descriptors. The secondary volume descriptor describes the volume attributes, the location of the root directory, the location of the path table group, and so on.
When using Japanese for identifiers such as volume names and publisher identifiers, record them in the secondary volume descriptor. The details of the secondary volume descriptor are shown in Table 3.5.

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 NB 00 NB NB NB NB NL NL NM NM DE D1 A1 A1 A1 D1S D1S D1S ND ND ND ND 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 Occurence of Type L Path Table Location of Optional Occurence of Type L Path Table Location of Occurence of Type M Path Table Location of Optional Occurence 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 Volume flag System volume name that uses LSN 0 to 15 Number of sectors in the entire unused volume Number of volumes in unused multi-volume = 1 Volume serial number at the time of multi-volume Logical block length Number of bytes in the entire path table Path table position in LSBF notation Reserve Path table position in MSBF notation Reserve Directory record of root directory Overall name during multi-volume Publisher identifier Data editor identifier Identification of data usage Copyright File name Abstract (summary) File name Bibliographic file name Creation date, time update date, time expiration date, time effective Date, time File structure Version number Reserved for future standardization Not specified Reserved for future standardization

■ Directory

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

Within 8 characters　
｜ Up to 3 characters, can be omitted　
｜ ｜ Numbers 1-32767 (always set to 1)
↓ ↓ ↓　
File identification → File name. Extension; version　
↑ ↑ ↑　
｜ ｜ Separator 2 "Semicolon"　
｜ Number of delimiters 1 "Period"　
｜　
Directory name: 8 characters or less　
(The root directory is 1 byte 00H)　

Table 3.6 Directory Records

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 NB NB N N N NB 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 position (LSN) Data length Recording date / time File flag File unit size Interleaved gap size Volume sequence number File identification length File identification / file name. Extension: Version / directory name Information for embedded system

● Recording date / time format

Table 3.7 Recording date / time format

Byte position	Mold	Field name	explanation
1 2 3 Four Five 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 from 1900 Month Date Minutes Seconds Difference from Greenwich Mean Time From -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 Four Five 6 7	Existence Directory Associated File Record Protection Reserved Reserved Multi-Extent	Invisible file directory File related file (= 0) Extended attribute record structure file protection file (= 0) Multiple extent files (= 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 the 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 xxxxxxxx; 1	File name: 8 characters or less Extension: 3 characters or less (optional) Edition number: Always 1
1	Directory name	Directory name: 8 characters or less Root directory is 1 byte 00H

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

● System information

The following extensions have been made to the ISO9660 standard.

Table 3.10 System Information

Byte position	Mold	Field name	explanation
14 5-6 7 8 9 10-14	NM 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 execute Reserved World read Reserved World execute File contains Form 1 sectors File contains Form 2 sectors File contains interleaved sector CD-DA file Directory	Contains Form 1 sector Includes Form 2 sector Includes interleaved sector CD-DA file directory file

■ Pass table

A pathtable record is recorded for each directory in the directory hierarchy. Pathtable records are numbered starting with 1 and the first record indicates the root directory.
The details of the path table record are shown below.

Table 3.12 Path table records

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 Extension leading LSN Parent directory entry number Directory name Only if the directory name is odd

■ User file

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

■ Other

● Directory structure

GAME-CD also supports subdirectory structures.

● Multi-volume

Does not support.

● Multi-session

Does not support.