View source for ROM header

The '''ROM header''' or '''disc ID'''{{fileref|Mega-CD Disc Format Specifications.pdf|page=25}} is a defined area of a video game cartridge ROM or CD-ROM used to identify software. [[Sega]] mandated that software include a header, both so the hardware understood what it was running, and for cataloguing purposes.

Sega's ROM headers were designed to be human readable, so details of compatible software can be understood quickly. The layout of these headers were dictated by Sega, and failure to conform with the company's guidelines could mean software would be rejected by Sega's quality assurance teams and be prevented from going on sale.

Sega's first ROM header scheme came into use with the [[Sega Mega Drive]] in late 1988, and were still being mandated for [[Sega Dreamcast]] releases twenty years later. Other video game platform holders have adopted different schemes (or indeed no schemes at all).

==Pre-Mega Drive==
Likely due to smaller cartridge (or card) sizes, no ROM header schemes were ever enforced for Sega's earlier systems (or add-ons), the [[SG-1000]], [[SC-3000]] and [[Sega Master System]]. They were also not enforced with [[Sega Game Gear]] software, likely for similar reasons, or its technical similarities with the Master System architecture.

==Mega Drive==
Guidelines for Sega Mega Drive software were the first to mandate the inclusion of ROM headers, and the same system would be used for [[Sega Mega-CD]], [[Sega 32X]] and [[Pico]] software in the early 1990s.

ROM headers for these systems must occupy 256 bytes of memory in the cartridge (or disc) from {{hex|$100}} to {{hex|$1FF}}, laid out as follows{{fileref|Mega-CD Disc Format Specifications.pdf|page=26}}:

{|class="prettytable" style="width:700px;"
!rowspan="2"|Offset
!colspan="16"|Contents
|-
!0||1||2||3||4||5||6||7||8||9||A||B||C||D||E||F
|-
|{{hex|$100}}
|colspan="16"|Hardware designation
|-
|{{hex|$110}}
|colspan="16"|Company code, date
|-
|{{hex|$120}}
|colspan="16" rowspan="3"|Domestic game title
|-
|{{hex|$130}}
|-
|{{hex|$140}}
|-
|{{hex|$150}}
|colspan="16" rowspan="3"|Overseas game title
|-
|{{hex|$160}}
|-
|{{hex|$170}}
|-
|{{hex|$180}}
|colspan="14"|Disc type, product no., version
|colspan="2"|Checksum
|-
|{{hex|$190}}
|colspan="16"|I/O info
|-
|{{hex|$1A0}}
|colspan="8"|ROM capacity
|colspan="8"|RAM capacity
|-
|{{hex|$1B0}}
|colspan="12"|External RAM data
|colspan="4"|Modem info
|-
|{{hex|$1C0}}
|colspan="8"|Modem info
|colspan="8"|SPACE
|-
|{{hex|$1D0}}
|colspan="16"|SPACE
|-
|{{hex|$1E0}}
|colspan="16"|SPACE
|-
|{{hex|$1F0}}
|colspan="16"|Regional compatibility
|}
===Contents breakdown===
====Hardware designation====
{|class="prettytable sortable"
!Hardware
!Designation
!class="unsortable"|Comments
|-
|[[Sega Mega Drive]]||<tt>SEGA MEGA DRIVE</tt>{{fileref|Mega-CD Disc Format Specifications.pdf|page=25}}||
|-
|[[Sega Genesis]]||<tt>SEGA GENESIS</tt>{{fileref|Mega-CD Disc Format Specifications.pdf|page=25}}||
|-
|[[Sega Mega-CD]]||<tt>SEGA MEGA DRIVE</tt>||No distinction is made between cartridge and CD-based software.
|-
|[[Sega CD]]||<tt>SEGA GENESIS</tt>||No distinction is made between cartridge and CD-based software.
|-
|[[Sega 32X]]||<tt>SEGA 32X</tt>||
|-
|[[Pico]]||<tt>SEGA PICO</tt>||
|}
If software was set to be released across multiple regions where hardware names differed, typically the Japanese hardware name took precedence (e.g. "Mega Drive" rather than "Genesis"). There were seemingly no rules dictating this, however.

====Company name/code and date====
The text <tt>(C)</tt> plus four characters to symbolise the company name{{fileref|Mega-CD Disc Format Specifications.pdf|page=25}}. This can literally just be the company name (e.g. <tt>SEGA</tt>), but also a company's [[Third-party T-series codes|T-series code]] in the form <tt>T-XX</tt> (where <tt>XX</tt> is a two-digit number).

The use of T-series numbers here pre-dates the period where Sega had more than a hundred licensed third-party publishers.

Dates were originally of the form <tt>NNNN.XXX</tt>, where NNNN would be a year, and XXX a three-letter month. 

Publishers had to be more creative after a certain point. For example, ''[[SeaQuest DSV]]'' published by [[THQ]] has <tt>(C)T-100 1994.12</tt> - a three digit T-series code, and a two-digit month.

====Domestic/overseas names====
The name of the software for both domestic (Japan) and overseas markets. These had to be filled in even if the software was exclusive to one region, and in most cases were kept the same.

For the Mega Drive at least, JIS kanji characters were permitted. This point is missing from later English revisions of the guidelines, suggesting Sega either started enforcing pure ASCII characters, or were either discouraging JIS outside of Japan.

====Software type, product code and version====
<tt>GM</tt> (game; T) or <tt>AI</tt> (educational) followed by the product code (C) and release version (V) in the form <tt>TT CCCCCC-VV</tt>{{fileref|Mega-CD Disc Format Specifications.pdf|page=25}}.

For example <tt>GM T-12345-00</tt> is a game with product code T-12345, version 0 (or the first release).

====I/O info====
Compatible accessories, represented by single characters{{fileref|Mega-CD Disc Format Specifications.pdf|page=25}}:
{|class="prettytable sortable"
!Accessory
!Code
|-
|[[Controller (Master System)|Master System controller]]||<tt>O</tt>
|-
|[[Control Pad (Mega Drive)|Mega Drive Control Pad]]||<tt>J</tt>
|-
|Keyboard ([[Mega Drive Keyboard]])||<tt>K</tt>
|-
|Serial I/O (RS232C)||<tt>R</tt>
|-
|Printer ([[4 Color Plotter Printer]])||<tt>P</tt>
|-
|Tablet ([[Sega Graphic Board]])||<tt>T</tt>
|-
|Trackball ([[Sports Pad]])||<tt>B</tt>
|-
|[[Paddle Control]]||<tt>V</tt>
|-
|Analog joystick ([[XE-1 AP]])||<tt>A</tt>
|-
|Mouse ([[Sega Mouse]], [[Mega Mouse]])||<tt>M</tt>
|-
|FDD ([[Mega Drive Floppy Disk Drive]])||<tt>F</tt>
|-
|CD-ROM ([[Sega Mega-CD]])||<tt>C</tt>
|-
|Multi-tap ([[Team Player]])||<tt>4</tt>
|-
|[[Six Button Control Pad (Mega Drive)|Six Button Control Pad]]||<tt>6</tt>
|}

====Modem info====
Details for the [[Mega Modem]]{{fileref|Mega-CD Disc Format Specifications.pdf|page=25}}. This was generally left unused as the peripheral did not release outside of Japan.

====Regional compatiblity====
Regions of the world where the software is intended to run. Sega changed its system at some point in 1994. 

=====1988 system=====
Prior to the change, regions were represented by one or more single characters{{fileref|Mega-CD Disc Format Specifications.pdf|page=26}}:
{|class="prettytable sortable"
!Region
!Code
|-
|NTSC-J||<tt>J</tt>
|-
|NTSC-U||<tt>U</tt>
|-
|PAL||<tt>E</tt>
|-
|}
"<tt>JUE</tt>" would mean the game was theoretically region free.

=====1994 system=====
Sega adjusted its system in 1994 to account for "Japanese PAL" systems. Now all regions were represented by a single byte, between 0 and F{{fileref|GenesisTechnicalBulletins.pdf|page=56}}:
{|class="prettytable"
!rowspan="2"|Hardware
!rowspan="2"|Region
!colspan="16"|Code
|-
!0
!1
!2
!3
!4
!5
!6
!7
!8
!9
!A
!B
!C
!D
!E
!F
|-
|Japan, NTSC
|Japan, South Korea, Taiwan
|{{no}}
|{{yes}}
|{{no}}
|{{yes}}
|{{no}}
|{{yes}}
|{{no}}
|{{yes}}
|{{no}}
|{{yes}}
|{{no}}
|{{yes}}
|{{no}}
|{{yes}}
|{{no}}
|{{yes}}
|-
|Japan, PAL
|(none)
|{{no}}
|{{no}}
|{{yes}}
|{{yes}}
|{{no}}
|{{no}}
|{{yes}}
|{{yes}}
|{{no}}
|{{no}}
|{{yes}}
|{{yes}}
|{{no}}
|{{no}}
|{{yes}}
|{{yes}}
|-
|Overseas, NTSC
|North America, Brazil
|{{no}}
|{{no}}
|{{no}}
|{{no}}
|{{yes}}
|{{yes}}
|{{yes}}
|{{yes}}
|{{no}}
|{{no}}
|{{no}}
|{{no}}
|{{yes}}
|{{yes}}
|{{yes}}
|{{yes}}
|-
|Overseas, PAL
|Europe, Hong Kong
|{{no}}
|{{no}}
|{{no}}
|{{no}}
|{{no}}
|{{no}}
|{{no}}
|{{no}}
|{{yes}}
|{{yes}}
|{{yes}}
|{{yes}}
|{{yes}}
|{{yes}}
|{{yes}}
|{{yes}}
|}
In this example:
*"<tt>0</tt>" would mean the game was incompatible with every console.
*"<tt>1</tt>" would mean the game was only compatible with NTSC-J consoles.
*"<tt>4</tt>" would mean the game was only compatible with NTSC-U consoles.
*"<tt>8</tt>" would mean the game was only compatible with PAL consoles.
*"<tt>F</tt>" would mean the game was compatible with all consoles.

Theoretically "<tt>E</tt>" could be mistaken for the older system (i.e. "Europe"/PAL), however this combination is rare, if not nonexistent.

====Space====
Some areas of the header should not be used, and instead filled with the ASCII space character ({{hex|$20}}){{fileref|Mega-CD Disc Format Specifications.pdf|page=26}}. It is possible these areas are remants of scrapped hardware plans.

===Example===
The following header is for the initial release of ''[[Sonic the Hedgehog (16-bit)|Sonic the Hedgehog]]'' for the Mega Drive:
{{ROMHeader|53 45 47 41 20 4D 45 47 41 20 44 52 49 56 45 20 28 43 29 53 45 47 41 20 31 39 39 31 2E 41 50 52 53 4F 4E 49 43 20 54 48 45 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 48 45 44 47 45 48 4F 47 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 53 4F 4E 49 43 20 54 48 45 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 48 45 44 47 45 48 4F 47 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 47 4D 20 30 30 30 30 31 30 30 39 2D 30 30 26 4A 4A 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 00 00 00 00 00 07 FF FF 00 FF 00 00 00 FF FF FF 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 4A 55 45 20 20 20 20 20 20 20 20 20 20 20 20 20}}
From the header alone, it can be established that:
*It is Mega Drive software
*The software was published by Sega
*The software is dated April 1991
*The software is known as "Sonic the Hedgehog" both domestically (Japan) and overseas.
*It is a game (GM) with product code "00001009-00"
*The software is compatible with the [[Control Pad (Mega Drive)|Control Pad]] (J)
*The software is designed to run on NTSC-J (J), NTSC-U (U) and PAL (E) systems.

==Saturn==
With the [[Sega Saturn]], the format was changed, and the official designation was '''system ID'''{{fileref|ST-040-R4-051795.pdf|page=29}}.

The system ID must exist at the start of the CD-ROM, occupying 256 bytes of memory, laid out as follows{{fileref|ST-040-R4-051795.pdf|page=29}}:

{|class="prettytable" style="width:700px;"
!rowspan="2"|Offset
!colspan="16"|Contents
|-
!0||1||2||3||4||5||6||7||8||9||A||B||C||D||E||F
|-
|{{hex|$00}}
|colspan="16"|Hardware identifier
|-
|{{hex|$10}}
|colspan="16"|Maker ID
|-
|{{hex|$20}}
|colspan="10"|Product number
|colspan="6"|Version
|-
|{{hex|$30}}
|colspan="8"|Release date
|colspan="8"|Device information
|-
|{{hex|$40}}
|colspan="10"|Compatible area symbols
|colspan="6"|Space
|-
|{{hex|$50}}
|colspan="16"|Compatible peripherals
|-
|{{hex|$60}}
|colspan="16" rowspan="7"|Game title
|-
|{{hex|$70}}
|-
|{{hex|$80}}
|-
|{{hex|$90}}
|-
|{{hex|$A0}}
|-
|{{hex|$B0}}
|-
|{{hex|$C0}}
|-
|{{hex|$D0}}
|colspan="16"|Reserved
|-
|{{hex|$E0}}
|colspan="4"|IP size
|colspan="4"|Reserved
|colspan="4"|Stack-M
|colspan="4"|Stack-S
|-
|{{hex|$F0}}
|colspan="4"|1st read address
|colspan="4"|1st read size
|colspan="4"|Reserved
|colspan="4"|Reserved
|}

All ASCII alphanumeric characters can be used in this section, as well as ".", "/", "-", ":" and space ({{hex|$20}}){{fileref|ST-040-R4-051795.pdf|page=30}}.

===Contents breakdown===
====Hardware identifier====
The name of the hardware. Only <tt>SEGA SEGASATURN </tt> was allowed{{fileref|ST-040-R4-051795.pdf|page=30}}, though this area may have been intended to cover future upgrades or add-ons.

====Maker ID====
The publisher responsible for the software. With Sega this was always <tt>SEGA ENTERPRISES</tt>{{fileref|ST-040-R4-051795.pdf|page=30}}, while third-parties had to use <tt>SEGA TP T-XXX   </tt> (where the XXX is the [[Third-party T-series codes|T-series code]]){{fileref|ST-040-R4-051795.pdf|page=30}}.

====Product number====
The unique product ID assigned by Sega. For first party Sega games this was of the form <tt>GS-XXXX    </tt> while third-parties used <tt>T-XXXXXX  </tt> (the Xs being replaced with the given number).

====Version====
The software version number. Sega enforced a versioning system in the form of <tt>VX.YYY</tt>. X could only be 0 (non-final) or 1 (final) while YYY could be a specific version number chosen by the publisher. <tt>V1.000</tt> would indicate a final "master" disc{{fileref|ST-040-R4-051795.pdf|page=31}}.

====Release date====
The creation date of the final master disc, in the form of <tt>YYYYMMDD</tt>. Sega's definition is misleading, as the mastering date was unlikely to be the physical release date (i.e. the date consumers could buy and play the game).

====Device information====
A field use for multi-disc software releases. Most software would use <tt>CD-1/1  </tt>, the first number being the disc number, and the second being the total number of discs{{fileref|ST-040-R4-051795.pdf|page=31}}.

For example, disc 2 of ''[[Panzer Dragoon Saga]]'' would be <tt>CD-2/4  </tt>.
 
====Compatible area symbol====
Regions of the world where the software is intended to run, represented by single characters{{fileref|ST-040-R4-051795.pdf|page=31}}. The Saturn added <tt>T</tt>, not seen with previous systems:
{|class="prettytable sortable"
!Region
!Code
|-
|NTSC-J (Japan)||<tt>J</tt>
|-
|NTSC-J (Taiwan, Philippines and Korea)||<tt>T</tt>
|-
|NTSC-U||<tt>U</tt>
|-
|PAL||<tt>E</tt>
|-
|}

====Compatible peripherals====
Compatible accessories, represented by single characters{{fileref|ST-040-R4-051795.pdf|page=32}}:
{|class="prettytable sortable"
!Accessory
!Code
|-
|[[Control Pad (Saturn)|Control Pad]]||<tt>J</tt>
|-
|Analog controller||<tt>A</tt>
|-
|Mouse ([[Shuttle Mouse]])||<tt>M</tt>
|-
|Keyboard ([[Saturn Keyboard]])||<tt>K</tt>
|-
|Steering controller ([[Arcade Racer]])||<tt>S</tt>
|-
|Multitap ([[6Player]])||<tt>T</tt>
|-
|[[Virtua Gun]]||<tt>G</tt>{{fileref|ST-TECH.pdf|page=126}}
|}

====Game title====
The name of the game. Unlike previous systems, all localised names were to be stored in this section. There were no rules as to how to format multiple names, only that they were "[able] to be distinguished easily"{{fileref|ST-040-R4-051795.pdf|page=32}}. 

====IP size====
The size of the Initial Program (IP){{fileref|ST-040-R4-051795.pdf|page=33}}.

====Stack-M====
Master-SH2 stack pointer address{{fileref|ST-040-R4-051795.pdf|page=33}}.

====Stack-S====
Slave-SH2 stack pointer address{{fileref|ST-040-R4-051795.pdf|page=33}}.

====1st read address====
Transfer destination address of files transferred to the WORK-RAM by the boot system while the Sega logo is being displayed{{fileref|ST-040-R4-051795.pdf|page=33}}.

====1st read size====
Ignored for CD-ROMs{{fileref|ST-040-R4-051795.pdf|page=33}}. This is likely a leftover from when cartridge-based games were still being considered for the Saturn platform.

====Reserved====
Reserved areas of the header should not be used, and instead filled with {{hex|$00}}{{fileref|ST-040-R4-051795.pdf|page=30}}. It is possible these areas are remants of scrapped hardware plans.

===Example===
{{ROMHeader|53 45 47 41 20 53 45 47 41 53 41 54 55 52 4E 20 53 45 47 41 20 54 50 20 54 2D 30 37 39 20 20 20 54 2D 30 37 39 30 34 48 35 30 56 32 2E 30 30 30 31 39 39 36 30 37 31 30 43 44 2D 31 2F 31 20 20 45 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 4A 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 4F 4C 59 4D 50 49 43 20 53 4F 43 43 45 52 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 06 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00|type=SAT}}

==Dreamcast==
{{IncompleteList}}
The [[Sega Dreamcast]] changed the scheme again, simplifying some sections and giving more space for the game title.

The header must exist at the start of the GD-ROM, occupying 256 bytes of memory, laid out as follows:

{|class="prettytable" style="width:700px;"
!rowspan="2"|Offset
!colspan="16"|Contents
|-
!0||1||2||3||4||5||6||7||8||9||A||B||C||D||E||F
|-
|{{hex|$00}}
|colspan="16"|Hardware identifier
|-
|{{hex|$10}}
|colspan="16"|Maker ID
|-
|{{hex|$20}}
|colspan="16"|Device information
|-
|{{hex|$30}}
|colspan="8"|Compatible area symbols
|colspan="8"|Compatible peripherals
|-
|{{hex|$40}}
|colspan="10"|Product number
|colspan="6"|Version
|-
|{{hex|$50}}
|colspan="16"|Release date
|-
|{{hex|$60}}
|colspan="16"|Boot filename
|-
|{{hex|$70}}
|colspan="16"|Disc manufacturer
|-
|{{hex|$80}}
|colspan="16" rowspan="8"|Game title
|-
|{{hex|$90}}
|-
|{{hex|$A0}}
|-
|{{hex|$B0}}
|-
|{{hex|$C0}}
|-
|{{hex|$D0}}
|-
|{{hex|$E0}}
|-
|{{hex|$F0}}
|}

===Content breakdown===
====Hardware identifier====
The name of the hardware. Only <tt>SEGA SEGAKATANA </tt> was allowed, though this area may have been intended to cover future upgrades or add-ons.

====Maker ID====
====Device information====
====Compatible area symbols====
====Compatible peripherals====
====Product number====
====Version====
====Release date====
====Boot filename====
====Disc manufacturer====
====Game title====

===Example===
{{ROMHeader|53 45 47 41 20 53 45 47 41 4B 41 54 41 4E 41 20 53 45 47 41 20 45 4E 54 45 52 50 52 49 53 45 53 36 31 41 37 20 47 44 2D 52 4F 4D 31 2F 31 20 20 20 55 20 20 20 20 20 20 30 37 39 39 41 31 30 20 54 34 30 32 30 36 4E 20 20 20 56 31 2E 30 30 31 32 30 30 30 30 34 32 30 20 20 20 20 20 20 20 20 31 53 54 5F 52 45 41 44 2E 42 49 4E 20 20 20 20 53 45 47 41 20 4C 43 2D 54 2D 34 30 32 20 20 20 53 55 50 45 52 20 4D 41 47 4E 45 54 49 43 20 4E 45 4F 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20|type=DC}}

==Issues==
===Inaccuracies===
While Sega usually policed the layout of ROM headers, they were less likely to moderate the ''contents'', meaning some headers do not accurately describe the software. For most users, the contents of ROM headers did not matter, as they wouldn't be shown when the software was running, however if one wishes to catalogue software based on the internal headers alone, the information can be misleading.

Most ROM headers were written while the software was in development and thus may not reflect the final product. The dates are particularly unreliable for this reason, however if a game changed publisher or gained new features late in development, this may not be reflected in the header's contents. As such, while in theory ROM headers should describe the software well enough for cataloguing, in practise the information can only provide rough guidelines.

Prototypes suggest that information was often added well in advance of software coming to market, with developers filling in the relevant fields to appease Sega's quality control, but not subsequently updating said fields when the product neared completion. This means headers often contain projected information, i.e. what the developers ''thought'' the software might look like sometimes months before the project fully took shape.

For example, ''Sonic the Hedgehog'''s header claims an April 1991 release and an incorrect product code. The game was originally planned for release around that time, but was delayed into June 1991, with the header not being updated. Furthermore the original ROM claims to be designed for NTSC-J systems, and while the game will indeed boot, Japan actually received a updated revision of the game in July, not the original release. 

===[[TradeMark Security System]]===
With the Mega Drive, Sega incorporated the ROM header into its TradeMark Security System (TMSS) license checking system. The first of these checks expects to see the text "SEGA" (or " SEGA") at {{hex|$100}}, the start of the hardware designation field. Starting in 1991, software that failed this check would not boot.

Early (and unlicensed) software often have ROM headers stored in the wrong place in memory (for example, ''[[Onslaught]]'' an unlicensed title by [[Accolade]] which infamously was never re-released to be TMSS-compliant, starts its header at {{hex|$108}}).

==References==
<references />

[[Category:Technical information]]