diff --git a/Ghost.ArcEntities/Archetype.cs b/Ghost.ArcEntities/Archetype.cs
new file mode 100644
index 0000000..8c41a47
--- /dev/null
+++ b/Ghost.ArcEntities/Archetype.cs
@@ -0,0 +1,127 @@
+using Misaki.HighPerformance.LowLevel.Buffer;
+using Misaki.HighPerformance.LowLevel.Collections;
+using Misaki.HighPerformance.LowLevel.Utilities;
+using System.Runtime.CompilerServices;
+
+namespace Ghost.ArcEntities;
+
+internal unsafe struct Archetype : IDisposable
+{
+    private UnsafeArray<int> _offsets;
+    private UnsafeArray<int> _componentIDs;
+    private UnsafeArray<int> _componentIDToOffset;
+    private int _entityCapacity;
+    private int _maxComponentID;
+
+    private UnsafeList<Chuck> _chunks;
+
+    public int EntityCapacity => _entityCapacity;
+
+    public Archetype(ReadOnlySpan<ComponentInfo> components)
+    {
+        _chunks = new UnsafeList<Chuck>(4, Allocator.Persistent);
+        CalculateLayout(components);
+    }
+
+    private void CalculateLayout(ReadOnlySpan<ComponentInfo> components)
+    {
+        var entitySize = sizeof(Entity);
+        var entityAlign = (int)MemoryUtility.AlignOf<Entity>();
+
+        // Calculate total size per entity to get an initial capacity estimate
+        var bytesPerEntity = entitySize;
+        _maxComponentID = 0;
+        for (var i = 0; i < components.Length; i++)
+        {
+            bytesPerEntity += components[i].size;
+            if (components[i].id > _maxComponentID)
+            {
+                _maxComponentID = components[i].id;
+            }
+        }
+
+        _entityCapacity = Chuck.CHUNK_SIZE / bytesPerEntity;
+        _componentIDToOffset = new UnsafeArray<int>(_maxComponentID + 1, Allocator.Persistent);
+        for (var i = 0; i < _componentIDToOffset.Count; ++i) _componentIDToOffset[i] = -1;
+
+        while (_entityCapacity > 0)
+        {
+            var currentOffset = 0;
+            var fits = true;
+
+            currentOffset = (currentOffset + entityAlign - 1) & ~(entityAlign - 1);
+            currentOffset += _entityCapacity * entitySize;
+
+            var entityOffset = currentOffset;
+            var tempOffsets = new int[components.Length];
+
+            for (var i = 0; i < components.Length; i++)
+            {
+                var size = components[i].size;
+                var align = components[i].alignment;
+
+                currentOffset = (currentOffset + align - 1) & ~(align - 1);
+                tempOffsets[i] = currentOffset;
+                currentOffset += _entityCapacity * size;
+
+                if (currentOffset > Chuck.CHUNK_SIZE)
+                {
+                    fits = false;
+                    break;
+                }
+            }
+
+            if (fits)
+            {
+                for (var i = 0; i < components.Length; i++)
+                {
+                    _componentIDToOffset[components[i].id] = tempOffsets[i];
+                }
+
+                return;
+            }
+
+            _entityCapacity--;
+        }
+    }
+
+    public Chuck CreateChunk()
+    {
+        var chunk = new Chuck(Chuck.CHUNK_SIZE, _entityCapacity);
+        _chunks.Add(chunk);
+
+        return chunk;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public UnsafeArray<T> GetComponentArray<T>(int chunkIndex)
+        where T : unmanaged
+    {
+        var id = ComponentType<T>.id;
+        if (id >= _componentIDToOffset.Count)
+        {
+            return default;
+        }
+
+        var offset = _componentIDToOffset[id];
+        if (offset == -1)
+        {
+            return default;
+        }
+
+        var chunk = _chunks[chunkIndex];
+        return new UnsafeArray<T>((T*)((byte*)chunk.GetUnsafePtr() + offset), _entityCapacity);
+    }
+
+    public void Dispose()
+    {
+        _componentIDToOffset.Dispose();
+
+        foreach (var chunk in _chunks)
+        {
+            chunk.Dispose();
+        }
+
+        _chunks.Dispose();
+    }
+}
diff --git a/Ghost.ArcEntities/AssemblyInfo.cs b/Ghost.ArcEntities/AssemblyInfo.cs
new file mode 100644
index 0000000..07c22ff
--- /dev/null
+++ b/Ghost.ArcEntities/AssemblyInfo.cs
@@ -0,0 +1,4 @@
+global using EntityID = System.Int32;
+global using GenerationID = System.UInt32;
+global using WorldID = System.UInt16;
+
diff --git a/Ghost.ArcEntities/Class1.cs b/Ghost.ArcEntities/Class1.cs
deleted file mode 100644
index 65bb0a8..0000000
--- a/Ghost.ArcEntities/Class1.cs
+++ /dev/null
@@ -1,6 +0,0 @@
-namespace Ghost.ArcEntities;
-
-public class Class1
-{
-
-}
diff --git a/Ghost.ArcEntities/Component.cs b/Ghost.ArcEntities/Component.cs
new file mode 100644
index 0000000..58dc143
--- /dev/null
+++ b/Ghost.ArcEntities/Component.cs
@@ -0,0 +1,66 @@
+using Misaki.HighPerformance.LowLevel.Collections;
+using Misaki.HighPerformance.LowLevel.Utilities;
+using Misaki.HighPerformance.LowLevel.Buffer;
+using System.Runtime.CompilerServices;
+
+namespace Ghost.ArcEntities;
+
+internal struct ComponentInfo
+{
+    public int size;
+    public int alignment;
+    public int id;
+}
+
+internal static unsafe class ComponentType<T>
+    where T : unmanaged
+{
+    public static readonly int Size = sizeof(T);
+    public static readonly int Alignment = (int)MemoryUtility.AlignOf<T>();
+    public static readonly int id = ComponentRegister.s_nextComponentTypeID++;
+
+    public static ComponentInfo GetInfo()
+    {
+        return new ComponentInfo
+        {
+            size = Size,
+            alignment = Alignment,
+            id = id
+        };
+    }
+}
+
+internal class ComponentRegister
+{
+    internal static int s_nextComponentTypeID = 0;
+}
+
+internal unsafe struct Chuck : IDisposable
+{
+    public const int CHUNK_SIZE = 16384; // 16 KB
+
+    private UnsafeArray<byte> _data;
+    private int _count;
+    private int _capacity;
+
+    public int Count => _count;
+    public int Capacity => _capacity;
+
+    public Chuck(int size, int capacity)
+    {
+        _data = new UnsafeArray<byte>(size, Allocator.Persistent);
+        _capacity = capacity;
+        _count = 0;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public byte* GetUnsafePtr()
+    {
+        return (byte*)_data.GetUnsafePtr();
+    }
+
+    public void Dispose()
+    {
+        _data.Dispose();
+    }
+}
diff --git a/Ghost.ArcEntities/Entity.cs b/Ghost.ArcEntities/Entity.cs
new file mode 100644
index 0000000..3f0e134
--- /dev/null
+++ b/Ghost.ArcEntities/Entity.cs
@@ -0,0 +1,81 @@
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace Ghost.ArcEntities;
+
+[StructLayout(LayoutKind.Sequential, Size = 8)]
+public struct Entity : IEquatable<Entity>, IComparable<Entity>
+{
+    public const EntityID INVALID_ID = -1;
+
+    private EntityID _id;
+    private GenerationID _generation;
+
+    public readonly EntityID ID
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => _id;
+    }
+
+    public readonly GenerationID Generation
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => _generation;
+    }
+
+    public readonly bool IsValid
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => ID != INVALID_ID;
+    }
+
+    public static Entity Invalid
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => new(INVALID_ID, GenerationID.MaxValue);
+    }
+
+    internal Entity(EntityID id, GenerationID generation)
+    {
+        _id = id;
+        _generation = generation;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    internal void IncrementGeneration() => _generation++;
+
+    public readonly bool Equals(Entity other)
+    {
+        return _id == other._id && _generation == other._generation;
+    }
+
+    public readonly int CompareTo(Entity other)
+    {
+        return _id.CompareTo(other._id);
+    }
+
+    public override readonly bool Equals(object? obj)
+    {
+        return obj is Entity other && Equals(other);
+    }
+
+    public override readonly int GetHashCode()
+    {
+        return _id.GetHashCode();
+    }
+
+    public static bool operator ==(Entity left, Entity right)
+    {
+        return left.Equals(right);
+    }
+
+    public static bool operator !=(Entity left, Entity right)
+    {
+        return !(left == right);
+    }
+
+    public override readonly string ToString()
+    {
+        return $"Entity {{ Index: {ID}, Generation: {Generation} }}";
+    }
+}
diff --git a/Ghost.ArcEntities/Ghost.ArcEntities.csproj b/Ghost.ArcEntities/Ghost.ArcEntities.csproj
index b760144..e73b545 100644
--- a/Ghost.ArcEntities/Ghost.ArcEntities.csproj
+++ b/Ghost.ArcEntities/Ghost.ArcEntities.csproj
@@ -4,6 +4,11 @@
     <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
 
+  <ItemGroup>
+        <ProjectReference Include="../Ghost.Core/Ghost.Core.csproj" />
+  </ItemGroup>
+
 </Project>
diff --git a/Ghost.ArcEntities/World.cs b/Ghost.ArcEntities/World.cs
new file mode 100644
index 0000000..98d0ee8
--- /dev/null
+++ b/Ghost.ArcEntities/World.cs
@@ -0,0 +1,109 @@
+using System.Runtime.CompilerServices;
+
+namespace Ghost.ArcEntities;
+
+public partial class World
+{
+    private static List<World> s_worlds = new(4);
+    private static Queue<WorldID> s_freeWorldSlots = new();
+
+    public static int WorldCount => s_worlds.Count - s_freeWorldSlots.Count;
+
+    public static World Create(int entityCapacity = 16)
+    {
+        lock (s_worlds)
+        {
+            if (s_freeWorldSlots.TryDequeue(out var index))
+            {
+                s_worlds[index] = new World(index, entityCapacity);
+            }
+            else
+            {
+                if (s_worlds.Count >= WorldID.MaxValue)
+                {
+                    throw new InvalidOperationException("Maximum number of worlds reached");
+                }
+
+                index = (WorldID)s_worlds.Count;
+                s_worlds.Add(new World(index, entityCapacity));
+            }
+
+            return s_worlds[index];
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static World GetWorld(int index)
+    {
+        return s_worlds[index];
+    }
+}
+
+public partial class World : IDisposable, IEquatable<World>
+{
+    private readonly WorldID _id;
+
+    private bool _isDisposed = false;
+
+    public WorldID ID => _id;
+
+    private World(WorldID id, int entityCapacity)
+    {
+        _id = id;
+    }
+
+    ~World()
+    {
+        Dispose();
+    }
+
+    public bool Equals(World? other)
+    {
+        if (other is null)
+        {
+            return false;
+        }
+
+        if (ReferenceEquals(this, other))
+        {
+            return true;
+        }
+
+        return _id == other._id;
+    }
+
+    public override int GetHashCode()
+    {
+        return _id.GetHashCode();
+    }
+
+    public override bool Equals(object? obj)
+    {
+        return obj is World other && Equals(other);
+    }
+
+    public static bool operator ==(World? left, World? right)
+    {
+        return left?.Equals(right) ?? right is null;
+    }
+
+    public static bool operator !=(World? left, World? right)
+    {
+        return !(left == right);
+    }
+
+    public void Dispose()
+    {
+        if (_isDisposed)
+        {
+            return;
+        }
+
+        s_freeWorldSlots.Enqueue(_id);
+
+        _isDisposed = true;
+
+        GC.SuppressFinalize(this);
+    }
+}
+