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Sonic News Network
Sonic News Network
This page is about a feature of the Sonic & Knuckles video game cartridge. For the move used by multiple playable characters, see Lock-on.

Sonic & Knuckles is a revolutionary new kind of game! It's the first game cartridge ever that you can play itself, or Lock-On with other Sonic game cartridges!

— Description, Sonic & Knuckles United States instruction booklet[1]

The lock-on technology label seen in box art and adverts.

Lock-on technology[2] (ロックオンシステム[3] Rokkuonshi Sutemu?, lit. "Lock-on System"), also written as Lock-On Technology[4] and simply Lock-On[1][5] (ロックオン[6] Rokkuon?), is a trademark feature for the Sonic & Knuckles game cartridges. The top of Sonic & Knuckles cartridge has an additional adapter slot, allowing players to insert different Sonic the Hedgehog game cartridges for the Sega Mega Drive into it, resulting one of three games becoming accessible to play: Sonic the Hedgehog 3 & Knuckles (Sonic the Hedgehog 3), Knuckles the Echidna in Sonic the Hedgehog 2 (Sonic the Hedgehog 2), and Blue Sphere with almost any other Mega Drive game. This feature offers new additions not found in the original games and changes to extend the gameplay experience, such as Knuckles the Echidna becoming a playable character in the lock-on games Knuckles in Sonic the Hedgehog 2 and Sonic the Hedgehog 3 & Knuckles.

During the game development, the lock-on technology was conceived as a workaround for developers at Sega Technical Institute when Sonic the Hedgehog 3 and Sonic & Knuckles were originally considered as one standalone game. Due to the troubled development and the game's scheduled February 1994 release, the production was split into two games, with Sonic the Hedgehog 3 being released as the first half, while pre-considered features such as a playable Knuckles in the single player mode and the latter half of Zones were shifted to the Sonic & Knuckles release about half a year later.[3] This resulted in the lock-on game, Sonic the Hedgehog 3 & Knuckles, which was the game the developers originally intended to release before it was split.[7][8][9]

Concept and creation

The North American cartridge of Sonic & Knuckles with the additional adapter slot on the top.

Two and a half years prior the development of Sonic the Hedgehog 3, the idea of backwards compatibility between game cartridges was conceived by Sega, namely between the releases of Sonic the Hedgehog (16-bit) and Sonic the Hedgehog 2 according to Roger Hector, the executive coordinator of Sonic the Hedgehog 3.[10] The early idea for the third mainline Sonic Sega Mega Drive game involved using the new Sega Virtua Processor chip ("SVP"), which allowed one to create isometric 3D graphics.[11] The development team at Sega Technical Institute included the SVP chip during the production of Sonic the Hedgehog 3 up until about June of 1993, where all the programming was abandoned due to cost issues and the realization that the SVP chip would not be finished by the end of the year, thus leaving only six months to finish the game[12] for its scheduled release of February 1994.[11]

Towards the end of 1993, the game had become so large in its scope that only half of the planned Zones had been finished at the time.[13][9] Also, due the size of the project and the lack of cartridge's limited data space,[7] it was decided to split the production into two games.[8][13] With two games being referred to as “3A” and “3B” during the production, Yuji Naka would state in an interview that the lock-on technology idea came from one of the staff member's question of combining two cartridges at the near end of the "3A" production.[11] This prompted the developers to turn to the hardware division, where they came to conclusion of including the game cartridge for the "3B" project with an additional adapter slot. By inserting the Sonic the Hedgehog 3 cartridge into the adapter slot, players could link the two games together to create the full game.[7][8]

With the release of Sonic the Hedgehog 3 in February 1994, the production of the "3B" portion, later named Sonic & Knuckles, proceed with the inclusion of the lock-on technology feature and the gameplay features originally conceived for Sonic the Hedgehog 3.[13][9] After being announced in Summer 1994,[14] the lock-on feature became one of the most notable elements on the game's marketing campaign,[6] with advertisements and promos claiming the game being backwards compatible with other Sonic the Hedgehog games.[15]


The Sonic & Knuckles game cartridge comes with a unique design compared to majority of other Sega Mega Drive games. The top part of the cartridge has a round hatch that can be opened to reveal an additional adapter slot for another Mega Drive cartridge to be inserted into it.[16][17] As a result of inserting the cartridge and booting up the console, the lock-on game becomes playable, which includes new gameplay features, changes to the original game, or content from two games having been mixed together. When doing this, the Sonic & Knuckles cartridge reads the ROM data from its attached lock-on game.[18] Inside the cartridge, the Sonic & Knuckles game itself takes up 2MB of the cartridge's ROM space (the maximum size of a Sega Mega Drive cartridge is 4MB) with the extra amount of space becoming accessible for the lock-on game. Also, if the lock-on game contains a battery pack, all the saved data on that cartridge will be erased. When Sonic the Hedgehog 2 is inserted on the other hand, the cartridge will start reading both ROM slots from Sonic & Knuckles and Sonic the Hedgehog 2, as well a separate, 256K ROM chip containing patch code that is specifically intended for the lock-on game Knuckles the Echidna in Sonic the Hedgehog 2.[19]

If the cartridge's memory size is larger than 2MB, the console will not run the lock-on game,[19] resulting in the console booting up the standalone Sonic & Knuckles game instead. Most of the game cartridges around and after the release of Sonic & Knuckles are larger than 4MB in terms of ROM size. The Sonic & Knuckles cartridge typically reads only the second half of the 4MB ROM. Also, because of the placement of the ROM header in the first half of the cartridge, it will not recognize it as a valid game. However, a notable exception for this is the compilation game Sonic Classics, as it has the Sonic the Hedgehog (16-bit) ROM placed in the second half of the cartridge data and contains the fake ROM header, which has been mapped into a location where the Sonic & Knuckles cartridge would read and recognize it as the same game.[19] Because of this, all of the Special Stage layouts in the lock-on game Blue Sphere will become available.

Sonic the Hedgehog 3

The title screen of Sonic the Hedgehog 3 & Knuckles.

When the Sonic the Hedgehog 3 cartridge is inserted into the adapter slot on the Sonic & Knuckles cartridge, the player gets access to the lock-on game Sonic the Hedgehog 3 & Knuckles, the combined title of both games with gameplay identical to the both of them. All fourteen Zones from two games become available along with Tails (and Sonic & Tails) and Knuckles becoming playable characters alongside Sonic.[20] All major features from Sonic the Hedgehog 3 are also available, including the save system and Competition mode. All three Bonus Stages from the two games are also accessible when the player enters the Star Circle with certain amount of Rings. Zones from Sonic the Hedgehog 3 in Sonic the Hedgehog 3 & Knuckles receive minor level layout changes and alternate object placements, including extension of Mushroom Hill Zone, exclusive pathways,[21] cinematic cutscenes and different boss fights against an Eggrobo for Knuckles. Music tracks from Sonic the Hedgehog 3 have also been replaced with Sonic & Knuckles tracks in the lock-on game, including the themes for Knuckles, mid-bosses, 1-Up, Invincibility and the end credits.

One of the new additions in the lock-on game are the Super Emeralds, which the player can collect after getting all seven Chaos Emeralds and clearing all the Special Stages with layouts identical to those in Sonic & Knuckles. Getting all Super Emeralds rewards the player with lock-on exclusive transformations: Hyper Sonic, Super Tails and Hyper Knuckles.

Sonic the Hedgehog 2

The title screen of Knuckles the Echidna in Sonic the Hedgehog 2.

Inserting the game cartridge of Sonic the Hedgehog 2 into the adapter slot results in a new game called Knuckles the Echidna in Sonic the Hedgehog 2. Unlike in Sonic the Hedgehog 3, Knuckles possesses the same moveset and attributes from Sonic & Knuckles and replaces Sonic as the playable character, while Tails only appears piloting Tornado in few Zones and during the ending cutscenes. Both the 2 Player VS or Options menus are not accessible, while many Zones have received additional object placements in different sections, which Knuckles can only reach with his Glide and Climb abilities.[22] Other notable changes include Knuckles being able to keep all of his Rings after exiting the Special Stage and alternate colors for Zone's title cards, Flickies and the Shield due to the playable character's limited color palette.

Sonic the Hedgehog and any other Sega Mega Drive game

Main article: Blue Sphere

The title screen of Blue Sphere.

If the player inserts almost any other Sega Mega Drive game cartridge into the slot adapter, a start-up screen featuring Sonic, Tails, Knuckles, and Dr. Robotnik posing on a black background is displayed, with an endlessly scrolling line showing the text "NO WAY? NO WAY!" on the top of the screen. At the start-up screen, the player has to press A Button (Sega Genesis).svg + B Button (Sega Genesis).svg + C Button (Sega Genesis).svg at the same time to gain access to one of the many Special Stages. In Blue Sphere, Sonic and Knuckles are playable characters, and the gameplay closely resembles the one in the Special Stages from Sonic the Hedgehog 3 and Sonic & Knuckles.

The Special Stage layouts in Blue Sphere are randomly generated when the player receives a unique level layout code. It also functions as a password when typing it in on the start-up screen. With it, the player gets to play only a single Special Stage without the password[16] whenever any other Sega Mega Drive cartridge is inserted into the adapter, as the Special Stage layout is based on the serial number of the cartridge's ROM header data.[19] When the player has inserted the Sonic the Hedgehog (16-bit) or Sonic Classics[19] cartridge into the Sonic & Knuckles adapter slot however, all 134,217,728 playable Special Stage layouts become available to play.[8] After clearing the 128,016,000th Special Stage, a couple of stages are recycled and the game starts to loop after the player has cleared all the Special Stage layouts.


After the original release of Sonic & Knuckles, multiple lock-on games were usually included as separate ROMs or simple ports. These are generally re-released on multiple compilations for different console platforms or on different subscription services on the PC. In Sonic Mega Collection and Sonic Mega Collection Plus, the player usually has to unlock these lock-on games separately by playing through already available games long enough to be accessed. The unusual exception to this is Sonic the Hedgehog 3 & Knuckles, which has been released on Steam; Sonic the Hedgehog 3 and Sonic & Knuckles have not been included separately on the same platform.

Lock-on menu depicting available games, from the Japanese release of Sonic & Knuckles.

There have been different cases where developers have attempted to loosely re-implement the lock-on technology experience in some form. In Sonic Jam, by choosing to play in Sonic & Knuckles, the player receives extra option of choosing one of three other available Sonic the Hedgehog games to play one of the locked-on games. Sonic & Knuckles Collection has two of three lock-on games to chosen along with Sonic the Hedgehog 3 and Sonic & Knuckles on the opening menu. When Sonic & Knuckles received its release on the Wii's Virtual Console, the player has a choice to play one of its lock-on expansions, if the Virtual Console releases of Sonic the Hedgehog (16-bit), Sonic the Hedgehog 2 or Sonic the Hedgehog 3 are already purchased on the same account.[4][23][24] While playing Sonic & Knuckles on Wii, the player has to press down the minus button on the Wii Remote or Classic Controller to activate the lock-on menu, although the game will be reset after changing the lock-on setting.

The Xbox Live Arcade port of Sonic & Knuckles includes lock-on games as separate bonus content.[25] The 2013 remaster of Sonic the Hedgehog 2 implements the remastered rendition of Knuckles the Echidna in Sonic the Hedgehog 2, allowing the player to choose Knuckles as the playable character, much like in the original lock-on game, albeit with extra features exclusive to the remaster.[note 1] Sega Ages: Sonic the Hedgehog 2 also includes the playable lock-on game Knuckles in Sonic the Hedgehog 2 along with Sonic the Hedgehog 2.[26]


Knuckles the Echidna in Sonic the Hedgehog (16-bit)

Knuckles the Echidna was not made officially playable in Sonic the Hedgehog (16-bit) until the 2013 re-release of the game.

Combining Sonic the Hedgehog (16-bit) and Sonic & Knuckles cartridges together does not result the additional lock-on game with Knuckles becoming a playable character in the first mainline game. Sonic & Knuckles designer, Takashi Iizuka, claimed years later that the development staff was unable to implement Knuckles into the game, stating "We realized that the construction of the world was really made for Sonic the Hedgehog 1 and when you started putting other characters into that world, it didn't really work right." The separate lock-on game Blue Sphere was included instead in order to avoid providing a bad gameplay experience for players.[7]

Simon Thomley (known as Stealth in the ROM hacking scene), would later make a modified ROM hack of Sonic the Hedgehog (16-bit) nicknamed "Knuckles in Sonic 1" in December 2005, which featured Knuckles as a playable character in an attempt to replicate the lock-on technology feature seen in Knuckles in Sonic the Hedgehog 2 and Sonic the Hedgehog 3 & Knuckles.[27] Years later, both Simon Thomley and Christian Whitehead would implement Knuckles as playable character in the 2013 remaster of Sonic the Hedgehog (16-bit), making it the first official release to have such a feature. In order to unlock Knuckles, the player has to obtain the six Chaos Emeralds in a separate playthrough.[28]

References in Sonic the Hedgehog games

The Cartridge buddy, from Sonic Runners.

Sonic Runners features a buddy called Cartridge that resembles a hovering Sonic & Knuckles cartridge locked-on with Sonic the Hedgehog (16-bit) on top of it and North American labels. It is a Rare Speed-type buddy that starts each Stage with a Combo, and was available on the Premium Roulette.

The lock-on technology is referenced twice in Sonic Mania and its expansion Sonic Mania Plus, where Studiopolis Zone Act 1 features one neon sign in the Zone's backdrop with the words sliding in to form stacked word "LOCK ON TECHNOLOGY". The feature is later referenced in Studiopolis Zone Act 2 with the word "LOCK ON" being formed by a clusters of tiles that can be flipped.


  • Even though the Sonic & Knuckles cartridge is perfectly compatible for the most of the non-Sonic cartridges for the Sega Mega Drive, a few known Mega Drive games released prior to the release of Sonic & Knuckles, such as Phantasy Star IV and the Mega Drive port of Super Street Fighter II: The New Challengers, do not support the lock-on feature due their exceptionally larger cartridge memory sizes (3MB and 5MB, respectively). However, western manuals of the game falsely claim that the adapter slot only supports Sonic the Hedgehog 2 and Sonic the Hedgehog 3 cartridges and it is not compatible with non-Sonic cartridges.[1][29]
  • Sega of Japan is reported to have original plans in early 1994 to release the game in Japan as 24 megabit cartridges rather than basic 16 megabit format at the time,[30] implying that Sonic the Hedgehog 3 and Sonic & Knuckles were set to be released on a single game cartridge without the lock-on technology feature. This shelved deluxe version known as Sonic the Hedgehog 3 Limited Edition in magazine articles, did not get far into the development process before Sega of Japan shifted its decision to releasing Sonic the Hedgehog 3 as 16 megabit cartridges, much like in the western market due to the game already having been sold at import shops in Japan.[30]

The mockup image featuring Knuckles in Green Hill Zone, from Sega Megazone #44.

  • Around the release of Sonic & Knuckles in Australia, the 44th issue of the gaming magazine Sega Megazone featured a small sub-section "Gnarly Knuckles" in the Sonic & Knuckles review with perceptible, cropped screenshot of Knuckles in Green Hill Zone from Sonic the Hedgehog (16-bit).[31] As stated earlier in the article, this would not occur when Sonic the Hedgehog (16-bit) and Sonic & Knuckles cartridges are combined together with the lock-on game revealed to the Blue Sphere instead.
  • Inserting a Sonic & Knuckles cartridge on top of another one has the player playing the regular Sonic & Knuckles game, much like without any lock-on game. However, placing multiple Sonic & Knuckles cartridges on top of each other will eventually result in the main game on the top becoming corrupted.[32]
  • Sega of Japan released a Japanese exclusive Sega Mega Drive Mini model called "Mega Drive Tower Mini" on 19 September 2019. The set includes Sega Mega Drive Mini with a micro Sega CD, Sega 32X, Sonic & Knuckles lock-on cartridge with Sonic the Hedgehog (16-bit) cartridge inserted on top of it.[33]
  • On 17 October 2021, Sonic Channel and Sonic the Hedgehog's Japanese social media account celebrated the 27th anniversary of Sonic & Knuckles's release with additional artwork illustrated by Yui Karasuno, which centered around the lock-on technology feature.[34]








  1. The gameplay experience is not identical to the original lock-on game: the color palette of the Zone title cards, Flickies and the Shield were reverted back to their original colors when playing as Knuckles.


  1. 1.0 1.1 1.2 Sonic & Knuckles (Sega Genesis) United States instruction booklet, pg. 2.
  2. Sonic & Knuckles by Sega for Sega Genesis. Sega. Archived from the original on 23 February 1998. Retrieved on 26 January 2022.
  3. 3.0 3.1 "ソニックチームの名はる作品だけしかついてない!?". Sega Magazine (Soft Bank) (3): 10. 13 December 1996. "中氏らが作った最後の「ソニック」シリズ。 制作はセガ・オプ・アメリカ。 半年後ロックオンシステムの「ソニック&ナックルズ」で完結。"
  4. 4.0 4.1 Sonic & Knuckles. Nintendo. Archived from the original on 16 February 2013. Retrieved on 26 January 2022.
  5. Sonic Jam (Sega Saturn) United States instruction booklet, pg. 7.
  6. 6.0 6.1 "誰もが驚いたロックオンシステム". Sega Magazine (Soft Bank) (8): 15. 13 June 1997. "MTVジャパンによって制作された「ソニック&ナックルズ」のCM。 "ロックオン"というキーワードが、さまざまな映像を絡め、印象づけられる内容となっていた。 CGも効果的だ。"
  7. 7.0 7.1 7.2 7.3 Shea, Brian (10 October 2016). How Sonic 3 Became Two Separate Games. Game Informer. Archived from the original on 14 October 2016. Retrieved on 27 January 2022.
  8. 8.0 8.1 8.2 8.3 "Sonic 3 & Knuckles - Behind the Scenes". GamesTM (Future Publishing) (60): 140–144. 9 August 2007.
  9. 9.0 9.1 9.2 Kemps, Heidi (30 September 2005). Sega's Yuji Naka Talks!. GameSpy. Archived from the original on 4 November 2005. Retrieved on 28 January 2022. "Sonic 3 is literally half a game. Sega management back then wanted the game out at a certain time and we only had half the stages done, so we had to put the leftovers into Sonic and Knuckles. So when you bought S&K and attached it to Sonic 3, you got the whole of what Sonic 3 was planned to have been."
  10. The Whizz (January 1995). "When Knuckles Met Sonic". GamePro (IDG Communications) (66): 20.
  11. 11.0 11.1 11.2 "ソニックザヘッジホッグ3 / 誰もが驚いたロックオンシステム". Sega Magazine (Soft Bank) (8): 15. 13 June 1997. Archived from the original.
  12. "誰もが驚いたロックオンシステム". Sega Magazine (Soft Bank): 15. 13 June 1997. "「3」の開発当初、SVPチップによる「3Dタイプ」の新しいソニックの開発を開始していた開発陣は、チップの製造の遅れによって それまで6カ月の開発資産をすべて捨てることになった。 「3」のアメリカでの発売予定が94年2月。 カートリッジROM製造に2~3カ月を要することを考えれば、開発陣にはたったの6 カ月程度しか猶予は残されていなかったのである。 中氏をはじめとする開発チームは、泣く泣く最終完成目標の約半分のボリュームである 6 ステージ分での発売に踏み切らざるを得なかったわけだ。 だが なんとか「3」を完結させたい彼らは、冗談のような驚異の手段を発明する。 それが"ロックオンシステム" である。"
  13. 13.0 13.1 13.2 Roger Hector: Director of STI Interviews [Sept/Oct 2005]. Secrets of Sonic Team. Archived from the original on 14 January 2007. Retrieved on 28 January 2022.
  14. "誰もが驚いたロックオンシステム". Sega Magazine (Soft Bank) (8): 15. 13 June 1997. "'94年夏。 謎のロゴだけが公開され、イメージ宣伝が続けられた「ソニック&ナックルズ」。 その正体は発売1 カ月前に公開されることに。"
  15. SEGA of America Sales Video - Sonic & Knuckles/32X (1994 Promo Video). YouTube (20 December 2011). Retrieved on 31 January 2022.
  16. 16.0 16.1 Sonic & Knuckles - Other Modes. Zone: 0 (8 June 2012). Archived from the original on 7 September 2012. Retrieved on 31 January 2022.
  17. Flynn, Ian; Sega (8 December 2021). Sonic the Hedgehog Encyclo-speed-ia. Dark Horse Books. p. 54. ISBN 978-1506719276. "The cartridge has a flip-up top that allows you to plug any other Sega Genesis / Mega Drive cartridge into it. Combining Sonic the Hedgehog 3 with Sonic & Knuckles gives you the complete experience."
  18. Thomley, Simon (18 October 2014). Sonic 3 (& Knuckles) 20th Anniversary. Archived from the original on 22 October 2014. Retrieved on 28 January 2022.
  19. 19.0 19.1 19.2 19.3 19.4 Burton, Jon (19 August 2020). SEGA's Crazy S&K "Lock-On Technology". YouTube. Retrieved on 27 January 2022.
  20. Sonic & Knuckles (Sega Genesis) United States instruction booklet, pg. 23.
  21. Sonic & Knuckles (Sega Genesis) United States instruction booklet, pg. 22.
  22. Sonic & Knuckles (Sega Genesis) United States instruction booklet, pg. 26.
  23. ソニック&ナックルズ (Japanese). Sega. Archived from the original on 17 July 2012. Retrieved on 25 January 2022.
  24. Sonic & Knuckles To Hit Japanese Virtual Console. Sonic Stadium (24 October 2009). Archived from the original on 7 May 2021. Retrieved on 25 January 2022.
  25. Xbox LIVE Marketplace - SONIC & KNUCKLES ™. Xbox Marketplace. Microsoft. Archived from the original on 10 September 2009. Retrieved on 5 February 2022.
  26. Lane, Gavin (15 January 2020). Knuckles The Echidna To Return In Lock-On Form To Sonic The Hedgehog 2 On Switch. Nintendo Life. Archived from the original on 30 November 2020. Retrieved on 26 January 2022.
  27. Mawson, Chris (29 May 2013). Sonic the Hedgehog 3 Remastered Interview with Simon 'Stealth' Thomley. TouchArcade. Archived from the original on 22 August 2015. Retrieved on 25 January 2022.
  28. A Guide to 'Sonic The Hedgehog' Version 2.0's Hidden Level-select, Debug Mode, and Many More Secrets. TouchArcade (29 May 2013). Archived from the original on 3 June 2013. Retrieved on 25 January 2022.
  29. Sonic & Knuckles (Sega Mega Drive) European instruction booklet, pg. 10.
  30. 30.0 30.1 "「ソニック3」は、なぜ16メカで発売されたの?". 週刊ファミ通 (ASCII): 93. 3 June 1994.
  31. "Mega Drive Review - Sonic & Knuckles". Sega Megazone (Megazone Publications) (44): 34. October 1994. "You'll tire of Sonic & Knuckles eventually... time to plug in another Sonic cart. That's right - you can 'piggy-back' other games in the series. S&K is programmed to read in levels from the other games and let you play them using the new characters' abilities. See what short work Knuckles makes of the Green Hill Zone."
  32. Bigley, Brendon (9 July 2014). What happens when you plug in 13 Sonic & Knuckles cartridges?. Pixelitis. Archived from the original on 13 July 2014. Retrieved on 27 January 2022.
  33. Dreadknux (4 June 2019). SEGA Reveals Mega Drive Mini CD, 32X, Sonic 1 and Sonic & Knuckles Decoration Models. Sonic Stadium. Archived from the original on 5 June 2019. Retrieved on 28 January 2022.
  34. ソニック・ザ・ヘッジホッグ【公式】 on Twitter (Japanese). Twitter (17 October 2021). Archived from the original on 17 October 2021. Retrieved on 26 January 2022.

Main article (Knuckles in Sonic 2) | Staff | Manuals | Glitches | Beta elements | Gallery | Pre-releases (Nick Arcade, Simon Wai) | Re-releases (2006, 2013, 3D, Sega Ages)

Main article (Sonic 3 & Knuckles) | Staff | Manuals | Glitches | Beta elements | Gallery

Main article (Blue Sphere, Knuckles in Sonic 2, Sonic 3 & Knuckles) | Credits | Manuals | Beta elements | Gallery

Main article | Script | Events | Gallery