diff --git a/packages/ecs/src/component.js b/packages/ecs/src/component.js
index 2b5ff02..0013927 100644
--- a/packages/ecs/src/component.js
+++ b/packages/ecs/src/component.js
@@ -51,7 +51,7 @@ class BaseComponent {
     return this.$$dirty;
   }
 
-  set dirty(dirty) {
+  setDirty(dirty) {
     this.$$dirty = dirty;
   }
 
@@ -84,9 +84,9 @@ class FlatComponent extends BaseComponent {
     // eslint-disable-next-line no-param-reassign
     count -= results.length;
     if (count > 0) {
-      const required = (this.caret + count) * this.schema.width;
+      const required = (this.caret + count) * this.constructor.width;
       if (required > this.data.byteLength) {
-        const chunkWidth = this.chunkSize * this.schema.width;
+        const chunkWidth = this.chunkSize * this.constructor.width;
         const remainder = required % chunkWidth;
         const extra = 0 === remainder ? 0 : chunkWidth - remainder;
         const size = required + extra;
@@ -111,7 +111,7 @@ class FlatComponent extends BaseComponent {
     const window = new this.Window(this.data, this);
     for (let i = 0; i < this.caret; ++i) {
       window.dirty = false;
-      window.cursor += this.schema.width;
+      window.cursor += this.constructor.width;
     }
     this.dirty = false;
   }
@@ -134,7 +134,8 @@ class FlatComponent extends BaseComponent {
           entity = entries[i];
         }
         this.map[entity] = allocated[i];
-        window.cursor = allocated[i] * this.schema.width;
+        window.cursor = allocated[i] * this.constructor.width;
+        window.entity = entity;
         for (const [i] of this.schema) {
           if (i in values) {
             window[i] = values[i];
@@ -155,7 +156,7 @@ class FlatComponent extends BaseComponent {
       this.Window = this.makeWindowClass();
     }
     const window = new this.Window(this.data, this);
-    window.cursor = this.map[entity] * this.schema.width;
+    window.cursor = this.map[entity] * this.constructor.width;
     return window;
   }
 
@@ -169,7 +170,7 @@ class FlatComponent extends BaseComponent {
     if (!this.window) {
       this.window = new this.Window(this.data, this);
     }
-    this.window.cursor = this.map[entity] * this.schema.width;
+    this.window.cursor = this.map[entity] * this.constructor.width;
     return this.window;
   }
 
@@ -194,18 +195,23 @@ class FlatComponent extends BaseComponent {
     }
     let offset = 0;
     const properties = {};
+    const {width} = this.constructor;
     const get = (type) => (
       `return this.view.get${Schema.viewMethodFromType(type)}(this.cursor + ${offset}, true);`
     );
     const set = (type) => [
-      'this.parent.dirty = true;',
+      `this.parent.setDirty(1, this.view.getBigUint64(this.cursor + ${width - 9}, true));`,
       `this.view.set${Schema.viewMethodFromType(type)}(this.cursor + ${offset}, v, true);`,
-      `this.view.setUint8(this.cursor + ${this.schema.width - 1}, 1, true);`,
+      `this.view.setUint8(this.cursor + ${width - 1}, 1, true);`,
     ].join('');
     /* eslint-disable no-new-func */
     properties.dirty = {
-      get: new Function('', `return !!this.view.getUint8(this.cursor + ${this.schema.width - 1}, true);`),
-      set: new Function('v', `this.view.setUint8(this.cursor + ${this.schema.width - 1}, v ? 1 : 0, true);`),
+      get: new Function('', `return !!this.view.getUint8(this.cursor + ${width - 1}, true);`),
+      set: new Function('v', `this.view.setUint8(this.cursor + ${width - 1}, v ? 1 : 0, true);`),
+    };
+    properties.entity = {
+      get: new Function('', `return this.view.getBigUint64(this.cursor + ${width - 9}, true);`),
+      set: new Function('v', `this.view.setBigUint64(this.cursor + ${width - 9}, v ? 1 : 0, true);`),
     };
     for (const [i, spec] of this.schema) {
       const {type} = spec;
@@ -229,7 +235,7 @@ class ArbitraryComponent extends BaseComponent {
 
   allocateMany(count) {
     if (!this.Instance) {
-      this.Instance = this.constructor.instanceFromSchema(this.schema);
+      this.Instance = this.instanceFromSchema();
     }
     const results = super.allocateMany(count);
     // eslint-disable-next-line no-param-reassign
@@ -248,7 +254,7 @@ class ArbitraryComponent extends BaseComponent {
     for (const i in this.map) {
       this.data[this.map[i]].dirty = false;
     }
-    this.dirty = false;
+    this.setDirty(false, 0);
   }
 
   createMany(entries) {
@@ -264,6 +270,7 @@ class ArbitraryComponent extends BaseComponent {
           entity = entries[i];
         }
         this.map[entity] = allocated[i];
+        this.data[allocated[i]].entity = entity;
         for (const j in values) {
           if (this.schema.has(j)) {
             this.data[allocated[i]][j] = values[j];
@@ -281,12 +288,16 @@ class ArbitraryComponent extends BaseComponent {
     return this.get(entity);
   }
 
-  static instanceFromSchema(schema) {
+  instanceFromSchema() {
+    const Component = this;
     const Instance = class {
 
+      $$dirty = 1;
+
+      $$entity = 0;
+
       constructor() {
-        this.$$dirty = 1;
-        for (const [i, {defaultValue}] of schema) {
+        for (const [i, {defaultValue}] of Component.schema) {
           this[i] = defaultValue;
         }
       }
@@ -301,7 +312,15 @@ class ArbitraryComponent extends BaseComponent {
         this.$$dirty = v;
       },
     };
-    for (const [i] of schema) {
+    properties.entity = {
+      get: function get() {
+        return this.$$entity;
+      },
+      set: function set(v) {
+        this.$$entity = v;
+      },
+    };
+    for (const [i] of Component.schema) {
       properties[i] = {
         get: function get() {
           return this[`$$${i}`];
@@ -309,6 +328,7 @@ class ArbitraryComponent extends BaseComponent {
         set: function set(v) {
           this[`$$${i}`] = v;
           this.$$dirty = 1;
+          Component.setDirty(1, this.entity);
         },
       };
     }
@@ -322,10 +342,11 @@ export default function ComponentRouter() {
   const schema = new Schema(this.constructor.schema);
   let RealClass;
   if (schema.width > 0) {
-    RealClass = FlatComponent;
+    RealClass = class extends FlatComponent {};
+    RealClass.width = schema.width + 9; // 1 for dirty, 8 for entity
   }
   else {
-    RealClass = ArbitraryComponent;
+    RealClass = class extends ArbitraryComponent {};
   }
   return new RealClass(schema);
 }
diff --git a/packages/ecs/src/ecs.js b/packages/ecs/src/ecs.js
index 20cf239..13116da 100644
--- a/packages/ecs/src/ecs.js
+++ b/packages/ecs/src/ecs.js
@@ -6,8 +6,6 @@ export default class Ecs {
 
   $$caret = 1;
 
-  $$cleanEntities = new Set();
-
   Components = {};
 
   dirty = new Set();
@@ -20,24 +18,15 @@ export default class Ecs {
 
   constructor(Components) {
     for (const i in Components) {
-      class Component extends Components[i] {
-
-        set dirty(dirty) {
-          super.dirty = dirty;
-          const it = this.$$cleanEntities.values();
-          let result = it.next();
-          while (!result.done) {
-            result = it.next();
-          }
-          for (let i = 0; i < this.$$entities.length; i++) {
-            if (this.get(this.$$entities[i])) {
-              this.dirty.add(this.$$entities[i]);
-            }
-          }
+      const comp = new Components[i]();
+      const {setDirty} = comp;
+      comp.setDirty = (dirty, entity) => {
+        setDirty.call(comp, dirty);
+        if (entity) {
+          this.dirty.add(entity);
         }
-
-      }
-      this.Components[i] = new Component();
+      };
+      this.Components[i] = comp;
     }
   }
 
@@ -143,7 +132,7 @@ export default class Ecs {
     for (const i in this.Components) {
       this.Components[i].clean();
     }
-    this.dirty = [];
+    this.dirty.clear();
   }
 
   tickFinalize() {
diff --git a/packages/ecs/src/index.js b/packages/ecs/src/index.js
index 769082a..0bed1f3 100644
--- a/packages/ecs/src/index.js
+++ b/packages/ecs/src/index.js
@@ -65,7 +65,9 @@ for (let i = 0; i < warm; ++i) {
 }
 performance.mark('tick0');
 ecs.tick(0.01);
+console.log(ecs.dirty.size);
 ecs.tickFinalize();
+console.log(ecs.dirty.size);
 performance.mark('tick1');
 console.log(ecs.$$systems[0].queries.default.count);
 
@@ -78,6 +80,7 @@ console.log({
   y: p.y,
   z: p.z,
   dirty: p.dirty,
+  entity: p.entity,
 });
 
 console.log(performance.getEntriesByType('measure').map(({duration, name}) => ({duration, name})));
diff --git a/packages/ecs/src/schema.js b/packages/ecs/src/schema.js
index 17883e2..f68f3e2 100644
--- a/packages/ecs/src/schema.js
+++ b/packages/ecs/src/schema.js
@@ -4,7 +4,7 @@ export default class Schema {
 
   defaultValues = {};
 
-  width = 1;
+  width = 0;
 
   spec;