Java Edition:Seed-Bedrock Block Mismatch
There have been several version ranges where bedrock either did not generate as intended, or was able to be broken. This results in a Seed-Bedrock Block Mismatch where the bedrock within the world does not match the generation that should occur within that seed. This can be done by placing bedrock using the bedrock item or to break bedrock using a unbreakable block removal method, but other methods exist to achieve this.
In the current version (1.21.7 (present)), bedrock can be found in every dimension. In the overworld, bedrock generates from -Y64 to -Y60 but prior to 21w06a (1.17 Snapshot) bedrock would generate between Y0 and Y4. In the nether there is a floor and roof to the dimension, bedrock generates from Y0 to Y4 and Y123 to Y127. In the end, bedrock generates on top of each obsidian tower, in the exit portal, and in the end gateways both from killing the Ender Dragon and those found in the Outer End Islands.
In 21w43a (1.18 Snapshot) old overworld bedrock floor layers between Y0 and Y4 are converted into Deepslate.
Obtaining
Bedrock Removal
Unbreakable block removal methods can be used to break bedrock, these methods are extremely versatile. Using this method, bedrock can be removed from any dimension. There have been unbreakable block removal methods from as early as Indev 20100206 all the way to 1.21.7 (present), making this a potential discontinued feature.
Bedrock Placement
If the bedrock item is obtained then the player can use it to place the bedrock anywhere within the world, in any dimension. This is the most versatile method to obtain this feature. The bedrock item can be obtained in many versions, most of the versions that bedrock can be obtained from include debug versions and April Fools' versions, but the item can be used even if updated out of these versions.
Bedrock Floor Pattern Change
The bedrock floors generation patter has changed several times throughout time, upgrading old bedrock floor patterns causes those old bedrock floor patterns to become discontinued as it is mismatched from the new pattern. This started in Infdev 20100616, and since then there have been nine different bedrock floor patterns.
List of Bedrock Floor Patterns
No Bedrock Chunks
From version pre-Classic rd-132211 to Infdev 20100615 bedrock did not generate at the bottom of the world. However, there are some Indev versions that did generate bedrock at the bottom of the world. These chunks can be loaded by left unpopulated, if these chunks are then repopulated in later versions then not only will no bedrock generate but the world will generate new stone types and biomes.
Some Bedrock Chunks
From version Infdev 20100616 to Alpha v1.1.2_01, bedrock would randomly not generate at the bottom of the world in a seemingly random pattern. These chunks can be loaded by left unpopulated, if these chunks are then repopulated in later versions then not only will no bedrock generate but the world will generate new stone types and biomes.
Sky Dimension in Overworld
In the version Beta 1.9 Prerelease 3 server, if the sky dimension chunks were generated they would be placed into the overworld folder instead of a separate folder. When these chunks were loaded, there would be no bedrock floor within those chunks. There are two methods to obtain sky dimension chunks in this version, the first method works by creating a new world and the other requires downgrading.
New World
Creating a new world in the version Beta 1.9 Prerelease 3 server, the spawn chunks would generate as sky dimension chunks instead of the correct overworld chunks.
End Dimension Player
Downgrading a player that is currently in the end[test] from Beta 1.9 Prerelease 4 to Beta 1.9 Prerelease 3 server will leave the player with the dimension=1 tag. With this tag, any new chunks that the player generates will be created using sky dimension chunks instead of the correct overworld chunks.
Sky Dimension Gallery
The spawn including sky dimension chunks with no bedrock floor.
Void End
In version 12w07a and 12w07b (1.2 snapshots), the main end island did not generate leaving only the obsidian platform that the player spawns on. This only occurs if the end is first loaded in this version and not in a previous version, when this happens the bedrock that normally generates on top of the obsidian pillars will not generation in addition to the rest of the island.
1.19 Blending Border
When upgrading a world from Unknown[test] through 1.18 to 1.19[test] through 1.19.1 Pre-Release 1, bedrock in the Nether on the borders between chunks with old blending and new blending may not generate properly leaving strips of air where bedrock should have generated.[1]
Work in Progress Sections
End Pillar Generation
Multiple Exit End Portals
(warning: may convert to end stone)
Pre-1.9 End Pillars
Farlands
Monoliths
Gallery
Infdev generated chunks from below.
Infdev chunks with no bedrock next to newly generated chunks.
Infdev chunks with no bedrock that were populated in newer version.
