diff --git a/addons/xterm-addon-attach/src/AttachAddon.api.ts b/addons/xterm-addon-attach/src/AttachAddon.api.ts
index 945824a209..c5b2d8587e 100644
--- a/addons/xterm-addon-attach/src/AttachAddon.api.ts
+++ b/addons/xterm-addon-attach/src/AttachAddon.api.ts
@@ -54,7 +54,7 @@ describe('AttachAddon', () => {
     const server = new WebSocket.Server({ port });
     const data = new Uint8Array([102, 111, 111]);
     server.on('connection', socket => socket.send(data));
-    await page.evaluate(`window.term.loadAddon(new window.AttachAddon(new WebSocket('ws://localhost:${port}'), { inputUtf8: true }))`);
+    await page.evaluate(`window.term.loadAddon(new window.AttachAddon(new WebSocket('ws://localhost:${port}')))`);
     assert.equal(await page.evaluate(`window.term.buffer.getLine(0).translateToString(true)`), 'foo');
     server.close();
   });
diff --git a/addons/xterm-addon-attach/src/AttachAddon.ts b/addons/xterm-addon-attach/src/AttachAddon.ts
index 9dc45ecbd3..117b2b5844 100644
--- a/addons/xterm-addon-attach/src/AttachAddon.ts
+++ b/addons/xterm-addon-attach/src/AttachAddon.ts
@@ -9,13 +9,11 @@ import { Terminal, IDisposable, ITerminalAddon } from 'xterm';
 
 interface IAttachOptions {
   bidirectional?: boolean;
-  inputUtf8?: boolean;
 }
 
 export class AttachAddon implements ITerminalAddon {
   private _socket: WebSocket;
   private _bidirectional: boolean;
-  private _utf8: boolean;
   private _disposables: IDisposable[] = [];
 
   constructor(socket: WebSocket, options?: IAttachOptions) {
@@ -23,17 +21,15 @@ export class AttachAddon implements ITerminalAddon {
     // always set binary type to arraybuffer, we do not handle blobs
     this._socket.binaryType = 'arraybuffer';
     this._bidirectional = (options && options.bidirectional === false) ? false : true;
-    this._utf8 = !!(options && options.inputUtf8);
   }
 
   public activate(terminal: Terminal): void {
-    if (this._utf8) {
-      this._disposables.push(addSocketListener(this._socket, 'message',
-        (ev: MessageEvent | Event | CloseEvent) => terminal.writeUtf8(new Uint8Array((ev as any).data as ArrayBuffer))));
-    } else {
-      this._disposables.push(addSocketListener(this._socket, 'message',
-        (ev: MessageEvent | Event | CloseEvent) => terminal.write((ev as any).data as string)));
-    }
+    this._disposables.push(
+      addSocketListener(this._socket, 'message', ev => {
+        const data: ArrayBuffer | string = ev.data;
+        terminal.write(typeof data === 'string' ? data : new Uint8Array(data));
+      })
+    );
 
     if (this._bidirectional) {
       this._disposables.push(terminal.onData(data => this._sendData(data)));
@@ -57,7 +53,7 @@ export class AttachAddon implements ITerminalAddon {
   }
 }
 
-function addSocketListener(socket: WebSocket, type: string, handler: (this: WebSocket, ev: MessageEvent | Event | CloseEvent) => any): IDisposable {
+function addSocketListener<K extends keyof WebSocketEventMap>(socket: WebSocket, type: K, handler: (this: WebSocket, ev: WebSocketEventMap[K]) => any): IDisposable {
   socket.addEventListener(type, handler);
   return {
     dispose: () => {
diff --git a/addons/xterm-addon-attach/typings/xterm-addon-attach.d.ts b/addons/xterm-addon-attach/typings/xterm-addon-attach.d.ts
index 8c66714089..1aa213574c 100644
--- a/addons/xterm-addon-attach/typings/xterm-addon-attach.d.ts
+++ b/addons/xterm-addon-attach/typings/xterm-addon-attach.d.ts
@@ -11,14 +11,6 @@ declare module 'xterm-addon-attach' {
      * Whether input should be written to the backend. Defaults to `true`.
      */
     bidirectional?: boolean;
-
-    /**
-     * Whether to use UTF8 binary transport for incoming messages. Defaults to `false`.
-     * Note: This must be in line with the server side of the websocket.
-     *       Always send string messages from the backend if this options is false,
-     *       otherwise always binary UTF8 data.
-     */
-    inputUtf8?: boolean;
   }
 
   export class AttachAddon implements ITerminalAddon {
diff --git a/addons/xterm-addon-search/src/SearchAddon.api.ts b/addons/xterm-addon-search/src/SearchAddon.api.ts
index f970fcc8b8..14e12a8c7b 100644
--- a/addons/xterm-addon-search/src/SearchAddon.api.ts
+++ b/addons/xterm-addon-search/src/SearchAddon.api.ts
@@ -111,12 +111,7 @@ async function openTerminal(options: ITerminalOptions = {}): Promise<void> {
 }
 
 async function writeSync(data: string): Promise<void> {
-  await page.evaluate(`window.term.write('${data}');`);
-  while (true) {
-    if (await page.evaluate(`window.term._core.writeBuffer.length === 0`)) {
-      break;
-    }
-  }
+  return page.evaluate(`new Promise(resolve => window.term.write('${data}', resolve))`);
 }
 
 function makeData(length: number): string {
diff --git a/addons/xterm-addon-webgl/src/WebglRenderer.api.ts b/addons/xterm-addon-webgl/src/WebglRenderer.api.ts
index b26790c484..66be22d930 100644
--- a/addons/xterm-addon-webgl/src/WebglRenderer.api.ts
+++ b/addons/xterm-addon-webgl/src/WebglRenderer.api.ts
@@ -145,12 +145,7 @@ async function openTerminal(options: ITerminalOptions = {}): Promise<void> {
 }
 
 async function writeSync(data: string): Promise<void> {
-  await page.evaluate(`window.term.write('${data}');`);
-  while (true) {
-    if (await page.evaluate(`window.term._core.writeBuffer.length === 0`)) {
-      break;
-    }
-  }
+  return page.evaluate(`new Promise(resolve => window.term.write('${data}', resolve))`);
 }
 
 async function getCellColor(col: number, row: number): Promise<number[]> {
diff --git a/demo/client.ts b/demo/client.ts
index 040292e4a2..92bac731b1 100644
--- a/demo/client.ts
+++ b/demo/client.ts
@@ -167,14 +167,7 @@ function createTerminal(): void {
 }
 
 function runRealTerminal(): void {
-  /**
-   * The demo defaults to string transport by default.
-   * To run it with UTF8 binary transport, swap comment on
-   * the lines below. (Must also be switched in server.js)
-   */
   term.loadAddon(new AttachAddon(socket));
-  // term.loadAddon(new AttachAddon(socket, {inputUtf8: true}));
-
   term._initialized = true;
 }
 
diff --git a/demo/server.js b/demo/server.js
index f1fae572af..a29875582b 100644
--- a/demo/server.js
+++ b/demo/server.js
@@ -4,10 +4,9 @@ var os = require('os');
 var pty = require('node-pty');
 
 /**
- * Whether to use UTF8 binary transport.
- * (Must also be switched in client.ts)
+ * Whether to use binary transport.
  */
-const USE_BINARY_UTF8 = false;
+const USE_BINARY = true;
 
 
 function startServer() {
@@ -46,7 +45,7 @@ function startServer() {
           rows: rows || 24,
           cwd: env.PWD,
           env: env,
-          encoding: USE_BINARY_UTF8 ? null : 'utf8'
+          encoding: USE_BINARY ? null : 'utf8'
         });
 
     console.log('Created terminal with PID: ' + term.pid);
@@ -108,7 +107,7 @@ function startServer() {
         }
       };
     }
-    const send = USE_BINARY_UTF8 ? bufferUtf8(ws, 5) : buffer(ws, 5);
+    const send = USE_BINARY ? bufferUtf8(ws, 5) : buffer(ws, 5);
 
     term.on('data', function(data) {
       try {
diff --git a/src/InputHandler.ts b/src/InputHandler.ts
index 56b2d8be17..74358583b4 100644
--- a/src/InputHandler.ts
+++ b/src/InputHandler.ts
@@ -324,7 +324,7 @@ export class InputHandler extends Disposable implements IInputHandler {
     super.dispose();
   }
 
-  public parse(data: string): void {
+  public parse(data: string | Uint8Array): void {
     let buffer = this._bufferService.buffer;
     const cursorStartX = buffer.x;
     const cursorStartY = buffer.y;
@@ -334,30 +334,17 @@ export class InputHandler extends Disposable implements IInputHandler {
     if (this._parseBuffer.length < data.length) {
       this._parseBuffer = new Uint32Array(data.length);
     }
-    this._parser.parse(this._parseBuffer, this._stringDecoder.decode(data, this._parseBuffer));
-
-    buffer = this._bufferService.buffer;
-    if (buffer.x !== cursorStartX || buffer.y !== cursorStartY) {
-      this._onCursorMove.fire();
-    }
-  }
-
-  public parseUtf8(data: Uint8Array): void {
-    let buffer = this._bufferService.buffer;
-    const cursorStartX = buffer.x;
-    const cursorStartY = buffer.y;
-
-    this._logService.debug('parsing data', data);
-
-    if (this._parseBuffer.length < data.length) {
-      this._parseBuffer = new Uint32Array(data.length);
-    }
-    this._parser.parse(this._parseBuffer, this._utf8Decoder.decode(data, this._parseBuffer));
+    this._parser.parse(this._parseBuffer,
+      (typeof data === 'string')
+        ? this._stringDecoder.decode(data, this._parseBuffer)
+        : this._utf8Decoder.decode(data, this._parseBuffer)
+    );
 
     buffer = this._bufferService.buffer;
     if (buffer.x !== cursorStartX || buffer.y !== cursorStartY) {
       this._onCursorMove.fire();
     }
+    this._terminal.refresh(this._dirtyRowService.start, this._dirtyRowService.end);
   }
 
   public print(data: Uint32Array, start: number, end: number): void {
diff --git a/src/Terminal.test.ts b/src/Terminal.test.ts
index 59864f0a35..667bf07640 100644
--- a/src/Terminal.test.ts
+++ b/src/Terminal.test.ts
@@ -29,11 +29,6 @@ describe('Terminal', () => {
     (<any>term).renderer = new MockRenderer();
     term.viewport = new MockViewport();
     (<any>term)._compositionHelper = new MockCompositionHelper();
-    // Force synchronous writes
-    term.write = (data) => {
-      term.writeBuffer.push(data);
-      (<any>term)._innerWrite();
-    };
     (<any>term).element = {
       classList: {
         toggle: () => { },
@@ -59,18 +54,18 @@ describe('Terminal', () => {
     // });
     it('should fire the onCursorMove event', (done) => {
       term.onCursorMove(() => done());
-      term.write('foo');
+      term.writeSync('foo');
     });
     it('should fire the onLineFeed event', (done) => {
       term.onLineFeed(() => done());
-      term.write('\n');
+      term.writeSync('\n');
     });
     it('should fire a scroll event when scrollback is created', (done) => {
       term.onScroll(() => done());
-      term.write('\n'.repeat(INIT_ROWS));
+      term.writeSync('\n'.repeat(INIT_ROWS));
     });
     it('should fire a scroll event when scrollback is cleared', (done) => {
-      term.write('\n'.repeat(INIT_ROWS));
+      term.writeSync('\n'.repeat(INIT_ROWS));
       term.onScroll(() => done());
       term.clear();
     });
@@ -195,7 +190,7 @@ describe('Terminal', () => {
     it('should clear a buffer larger than rows', () => {
       // Fill the buffer with dummy rows
       for (let i = 0; i < term.rows * 2; i++) {
-        term.write('test\n');
+        term.writeSync('test\n');
       }
 
       const promptLine = term.buffer.lines.get(term.buffer.ybase + term.buffer.y);
@@ -244,7 +239,7 @@ describe('Terminal', () => {
         assert.equal(e, '\x1b[200~foo\x1b[201~');
         done();
       });
-      term.write('\x1b[?2004h');
+      term.writeSync('\x1b[?2004h');
       term.paste('foo');
     });
   });
@@ -254,7 +249,7 @@ describe('Terminal', () => {
       let startYDisp: number;
       beforeEach(() => {
         for (let i = 0; i < INIT_ROWS * 2; i++) {
-          term.writeln('test');
+          term.writeSync('test\r\n');
         }
         startYDisp = INIT_ROWS + 1;
       });
@@ -289,7 +284,7 @@ describe('Terminal', () => {
       let startYDisp: number;
       beforeEach(() => {
         for (let i = 0; i < term.rows * 3; i++) {
-          term.writeln('test');
+          term.writeSync('test\r\n');
         }
         startYDisp = (term.rows * 2) + 1;
       });
@@ -312,7 +307,7 @@ describe('Terminal', () => {
     describe('scrollToTop', () => {
       beforeEach(() => {
         for (let i = 0; i < term.rows * 3; i++) {
-          term.writeln('test');
+          term.writeSync('test\r\n');
         }
       });
       it('should scroll to the top', () => {
@@ -326,7 +321,7 @@ describe('Terminal', () => {
       let startYDisp: number;
       beforeEach(() => {
         for (let i = 0; i < term.rows * 3; i++) {
-          term.writeln('test');
+          term.writeSync('test\r\n');
         }
         startYDisp = (term.rows * 2) + 1;
       });
@@ -347,7 +342,7 @@ describe('Terminal', () => {
       let startYDisp: number;
       beforeEach(() => {
         for (let i = 0; i < term.rows * 3; i++) {
-          term.writeln('test');
+          term.writeSync('test\r\n');
         }
         startYDisp = (term.rows * 2) + 1;
       });
@@ -392,7 +387,7 @@ describe('Terminal', () => {
       it('should not scroll down, when a custom keydown handler prevents the event', () => {
         // Add some output to the terminal
         for (let i = 0; i < term.rows * 3; i++) {
-          term.writeln('test');
+          term.writeSync('test\r\n');
         }
         const startYDisp = (term.rows * 2) + 1;
         term.attachCustomKeyEventHandler(() => {
@@ -737,7 +732,7 @@ describe('Terminal', () => {
       const high = String.fromCharCode(0xD800);
       const cell = new CellData();
       for (let i = 0xDC00; i <= 0xDCFF; ++i) {
-        term.write(high + String.fromCharCode(i));
+        term.writeSync(high + String.fromCharCode(i));
         const tchar = term.buffer.lines.get(0).loadCell(0, cell);
         expect(tchar.getChars()).eql(high + String.fromCharCode(i));
         expect(tchar.getChars().length).eql(2);
@@ -751,7 +746,7 @@ describe('Terminal', () => {
       const cell = new CellData();
       for (let i = 0xDC00; i <= 0xDCFF; ++i) {
         term.buffer.x = term.cols - 1;
-        term.write(high + String.fromCharCode(i));
+        term.writeSync(high + String.fromCharCode(i));
         expect(term.buffer.lines.get(0).loadCell(term.buffer.x - 1, cell).getChars()).eql(high + String.fromCharCode(i));
         expect(term.buffer.lines.get(0).loadCell(term.buffer.x - 1, cell).getChars().length).eql(2);
         expect(term.buffer.lines.get(1).loadCell(0, cell).getChars()).eql('');
@@ -764,7 +759,7 @@ describe('Terminal', () => {
       for (let i = 0xDC00; i <= 0xDCFF; ++i) {
         term.buffer.x = term.cols - 1;
         term.wraparoundMode = true;
-        term.write('a' + high + String.fromCharCode(i));
+        term.writeSync('a' + high + String.fromCharCode(i));
         expect(term.buffer.lines.get(0).loadCell(term.cols - 1, cell).getChars()).eql('a');
         expect(term.buffer.lines.get(1).loadCell(0, cell).getChars()).eql(high + String.fromCharCode(i));
         expect(term.buffer.lines.get(1).loadCell(0, cell).getChars().length).eql(2);
@@ -782,7 +777,7 @@ describe('Terminal', () => {
         if (width !== 1) {
           continue;
         }
-        term.write('a' + high + String.fromCharCode(i));
+        term.writeSync('a' + high + String.fromCharCode(i));
         // auto wraparound mode should cut off the rest of the line
         expect(term.buffer.lines.get(0).loadCell(term.cols - 1, cell).getChars()).eql(high + String.fromCharCode(i));
         expect(term.buffer.lines.get(0).loadCell(term.cols - 1, cell).getChars().length).eql(2);
@@ -794,8 +789,8 @@ describe('Terminal', () => {
       const high = String.fromCharCode(0xD800);
       const cell = new CellData();
       for (let i = 0xDC00; i <= 0xDCFF; ++i) {
-        term.write(high);
-        term.write(String.fromCharCode(i));
+        term.writeSync(high);
+        term.writeSync(String.fromCharCode(i));
         const tchar = term.buffer.lines.get(0).loadCell(0, cell);
         expect(tchar.getChars()).eql(high + String.fromCharCode(i));
         expect(tchar.getChars().length).eql(2);
@@ -809,7 +804,7 @@ describe('Terminal', () => {
   describe('unicode - combining characters', () => {
     const cell = new CellData();
     it('café', () => {
-      term.write('cafe\u0301');
+      term.writeSync('cafe\u0301');
       term.buffer.lines.get(0).loadCell(3, cell);
       expect(cell.getChars()).eql('e\u0301');
       expect(cell.getChars().length).eql(2);
@@ -817,7 +812,7 @@ describe('Terminal', () => {
     });
     it('café - end of line', () => {
       term.buffer.x = term.cols - 1 - 3;
-      term.write('cafe\u0301');
+      term.writeSync('cafe\u0301');
       term.buffer.lines.get(0).loadCell(term.cols - 1, cell);
       expect(cell.getChars()).eql('e\u0301');
       expect(cell.getChars().length).eql(2);
@@ -829,7 +824,7 @@ describe('Terminal', () => {
     });
     it('multiple combined é', () => {
       term.wraparoundMode = true;
-      term.write(Array(100).join('e\u0301'));
+      term.writeSync(Array(100).join('e\u0301'));
       for (let i = 0; i < term.cols; ++i) {
         term.buffer.lines.get(0).loadCell(i, cell);
         expect(cell.getChars()).eql('e\u0301');
@@ -843,7 +838,7 @@ describe('Terminal', () => {
     });
     it('multiple surrogate with combined', () => {
       term.wraparoundMode = true;
-      term.write(Array(100).join('\uD800\uDC00\u0301'));
+      term.writeSync(Array(100).join('\uD800\uDC00\u0301'));
       for (let i = 0; i < term.cols; ++i) {
         term.buffer.lines.get(0).loadCell(i, cell);
         expect(cell.getChars()).eql('\uD800\uDC00\u0301');
@@ -861,18 +856,18 @@ describe('Terminal', () => {
     const cell = new CellData();
     it('cursor movement even', () => {
       expect(term.buffer.x).eql(0);
-      term.write('￥');
+      term.writeSync('￥');
       expect(term.buffer.x).eql(2);
     });
     it('cursor movement odd', () => {
       term.buffer.x = 1;
       expect(term.buffer.x).eql(1);
-      term.write('￥');
+      term.writeSync('￥');
       expect(term.buffer.x).eql(3);
     });
     it('line of ￥ even', () => {
       term.wraparoundMode = true;
-      term.write(Array(50).join('￥'));
+      term.writeSync(Array(50).join('￥'));
       for (let i = 0; i < term.cols; ++i) {
         term.buffer.lines.get(0).loadCell(i, cell);
         if (i % 2) {
@@ -893,7 +888,7 @@ describe('Terminal', () => {
     it('line of ￥ odd', () => {
       term.wraparoundMode = true;
       term.buffer.x = 1;
-      term.write(Array(50).join('￥'));
+      term.writeSync(Array(50).join('￥'));
       for (let i = 1; i < term.cols - 1; ++i) {
         term.buffer.lines.get(0).loadCell(i, cell);
         if (!(i % 2)) {
@@ -918,7 +913,7 @@ describe('Terminal', () => {
     it('line of ￥ with combining odd', () => {
       term.wraparoundMode = true;
       term.buffer.x = 1;
-      term.write(Array(50).join('￥\u0301'));
+      term.writeSync(Array(50).join('￥\u0301'));
       for (let i = 1; i < term.cols - 1; ++i) {
         term.buffer.lines.get(0).loadCell(i, cell);
         if (!(i % 2)) {
@@ -942,7 +937,7 @@ describe('Terminal', () => {
     });
     it('line of ￥ with combining even', () => {
       term.wraparoundMode = true;
-      term.write(Array(50).join('￥\u0301'));
+      term.writeSync(Array(50).join('￥\u0301'));
       for (let i = 0; i < term.cols; ++i) {
         term.buffer.lines.get(0).loadCell(i, cell);
         if (i % 2) {
@@ -963,7 +958,7 @@ describe('Terminal', () => {
     it('line of surrogate fullwidth with combining odd', () => {
       term.wraparoundMode = true;
       term.buffer.x = 1;
-      term.write(Array(50).join('\ud843\ude6d\u0301'));
+      term.writeSync(Array(50).join('\ud843\ude6d\u0301'));
       for (let i = 1; i < term.cols - 1; ++i) {
         term.buffer.lines.get(0).loadCell(i, cell);
         if (!(i % 2)) {
@@ -987,7 +982,7 @@ describe('Terminal', () => {
     });
     it('line of surrogate fullwidth with combining even', () => {
       term.wraparoundMode = true;
-      term.write(Array(50).join('\ud843\ude6d\u0301'));
+      term.writeSync(Array(50).join('\ud843\ude6d\u0301'));
       for (let i = 0; i < term.cols; ++i) {
         term.buffer.lines.get(0).loadCell(i, cell);
         if (i % 2) {
@@ -1010,11 +1005,11 @@ describe('Terminal', () => {
   describe('insert mode', () => {
     const cell = new CellData();
     it('halfwidth - all', () => {
-      term.write(Array(9).join('0123456789').slice(-80));
+      term.writeSync(Array(9).join('0123456789').slice(-80));
       term.buffer.x = 10;
       term.buffer.y = 0;
       term.insertMode = true;
-      term.write('abcde');
+      term.writeSync('abcde');
       expect(term.buffer.lines.get(0).length).eql(term.cols);
       expect(term.buffer.lines.get(0).loadCell(10, cell).getChars()).eql('a');
       expect(term.buffer.lines.get(0).loadCell(14, cell).getChars()).eql('e');
@@ -1022,11 +1017,11 @@ describe('Terminal', () => {
       expect(term.buffer.lines.get(0).loadCell(79, cell).getChars()).eql('4');
     });
     it('fullwidth - insert', () => {
-      term.write(Array(9).join('0123456789').slice(-80));
+      term.writeSync(Array(9).join('0123456789').slice(-80));
       term.buffer.x = 10;
       term.buffer.y = 0;
       term.insertMode = true;
-      term.write('￥￥￥');
+      term.writeSync('￥￥￥');
       expect(term.buffer.lines.get(0).length).eql(term.cols);
       expect(term.buffer.lines.get(0).loadCell(10, cell).getChars()).eql('￥');
       expect(term.buffer.lines.get(0).loadCell(11, cell).getChars()).eql('');
@@ -1035,16 +1030,16 @@ describe('Terminal', () => {
       expect(term.buffer.lines.get(0).loadCell(79, cell).getChars()).eql('3');
     });
     it('fullwidth - right border', () => {
-      term.write(Array(41).join('￥'));
+      term.writeSync(Array(41).join('￥'));
       term.buffer.x = 10;
       term.buffer.y = 0;
       term.insertMode = true;
-      term.write('a');
+      term.writeSync('a');
       expect(term.buffer.lines.get(0).length).eql(term.cols);
       expect(term.buffer.lines.get(0).loadCell(10, cell).getChars()).eql('a');
       expect(term.buffer.lines.get(0).loadCell(11, cell).getChars()).eql('￥');
       expect(term.buffer.lines.get(0).loadCell(79, cell).getChars()).eql('');  // fullwidth char got replaced
-      term.write('b');
+      term.writeSync('b');
       expect(term.buffer.lines.get(0).length).eql(term.cols);
       expect(term.buffer.lines.get(0).loadCell(11, cell).getChars()).eql('b');
       expect(term.buffer.lines.get(0).loadCell(12, cell).getChars()).eql('￥');
diff --git a/src/Terminal.ts b/src/Terminal.ts
index 098c383b58..63400bcb9e 100644
--- a/src/Terminal.ts
+++ b/src/Terminal.ts
@@ -62,25 +62,11 @@ import { ILinkifier, IMouseZoneManager, LinkMatcherHandler, ILinkMatcherOptions,
 import { DirtyRowService } from 'common/services/DirtyRowService';
 import { InstantiationService } from 'common/services/InstantiationService';
 import { CoreMouseService } from 'common/services/CoreMouseService';
+import { WriteBuffer } from 'common/input/WriteBuffer';
 
 // Let it work inside Node.js for automated testing purposes.
 const document = (typeof window !== 'undefined') ? window.document : null;
 
-/**
- * The amount of write requests to queue before sending an XOFF signal to the
- * pty process. This number must be small in order for ^C and similar sequences
- * to be responsive.
- */
-const WRITE_BUFFER_PAUSE_THRESHOLD = 5;
-
-/**
- * The max number of ms to spend on writes before allowing the renderer to
- * catch up with a 0ms setTimeout. A value of < 33 to keep us close to
- * 30fps, and a value of < 16 to try to run at 60fps. Of course, the real FPS
- * depends on the time it takes for the renderer to draw the frame.
- */
-const WRITE_TIMEOUT_MS = 12;
-const WRITE_BUFFER_LENGTH_THRESHOLD = 50;
 
 export class Terminal extends Disposable implements ITerminal, IDisposable, IInputHandlingTerminal {
   public textarea: HTMLTextAreaElement;
@@ -153,21 +139,8 @@ export class Terminal extends Disposable implements ITerminal, IDisposable, IInp
   public params: (string | number)[];
   public currentParam: string | number;
 
-  // user input states
-  public writeBuffer: string[];
-  public writeBufferUtf8: Uint8Array[];
-  private _writeInProgress: boolean;
-
-  /**
-   * Whether _xterm.js_ sent XOFF in order to catch up with the pty process.
-   * This is a distinct state from writeStopped so that if the user requested
-   * XOFF via ^S that it will not automatically resume when the writeBuffer goes
-   * below threshold.
-   */
-  private _xoffSentToCatchUp: boolean;
-
-  /** Whether writing has been stopped as a result of XOFF */
-  // private _writeStopped: boolean;
+  // write buffer
+  private _writeBuffer: WriteBuffer;
 
   // Store if user went browsing history in scrollback
   private _userScrolling: boolean;
@@ -258,6 +231,8 @@ export class Terminal extends Disposable implements ITerminal, IDisposable, IInp
 
     this._setupOptionsListeners();
     this._setup();
+
+    this._writeBuffer = new WriteBuffer(data => this._inputHandler.parse(data));
   }
 
   public dispose(): void {
@@ -306,13 +281,6 @@ export class Terminal extends Disposable implements ITerminal, IDisposable, IInp
     this.params = [];
     this.currentParam = 0;
 
-    // user input states
-    this.writeBuffer = [];
-    this.writeBufferUtf8 = [];
-    this._writeInProgress = false;
-
-    this._xoffSentToCatchUp = false;
-    // this._writeStopped = false;
     this._userScrolling = false;
 
     // Register input handler and refire/handle events
@@ -1144,168 +1112,6 @@ export class Terminal extends Disposable implements ITerminal, IDisposable, IInp
     }
   }
 
-  /**
-   * Writes raw utf8 bytes to the terminal.
-   * @param data UintArray with UTF8 bytes to write to the terminal.
-   */
-  public writeUtf8(data: Uint8Array): void {
-    // Ensure the terminal isn't disposed
-    if (this._isDisposed) {
-      return;
-    }
-
-    // Ignore falsy data values
-    if (!data) {
-      return;
-    }
-
-    this.writeBufferUtf8.push(data);
-
-    // Send XOFF to pause the pty process if the write buffer becomes too large so
-    // xterm.js can catch up before more data is sent. This is necessary in order
-    // to keep signals such as ^C responsive.
-    if (this.options.useFlowControl && !this._xoffSentToCatchUp && this.writeBufferUtf8.length >= WRITE_BUFFER_PAUSE_THRESHOLD) {
-      // XOFF - stop pty pipe
-      // XON will be triggered by emulator before processing data chunk
-      this._coreService.triggerDataEvent(C0.DC3);
-      this._xoffSentToCatchUp = true;
-    }
-
-    if (!this._writeInProgress && this.writeBufferUtf8.length > 0) {
-      // Kick off a write which will write all data in sequence recursively
-      this._writeInProgress = true;
-      // Kick off an async innerWrite so more writes can come in while processing data
-      setTimeout(() => {
-        this._innerWriteUtf8();
-      });
-    }
-  }
-
-  protected _innerWriteUtf8(bufferOffset: number = 0): void {
-    // Ensure the terminal isn't disposed
-    if (this._isDisposed) {
-      this.writeBufferUtf8 = [];
-    }
-
-    const startTime = Date.now();
-    while (this.writeBufferUtf8.length > bufferOffset) {
-      const data = this.writeBufferUtf8[bufferOffset];
-      bufferOffset++;
-
-      // If XOFF was sent in order to catch up with the pty process, resume it if
-      // we reached the end of the writeBuffer to allow more data to come in.
-      if (this._xoffSentToCatchUp && this.writeBufferUtf8.length === bufferOffset) {
-        this._coreService.triggerDataEvent(C0.DC1);
-        this._xoffSentToCatchUp = false;
-      }
-
-      this._inputHandler.parseUtf8(data);
-
-      this.refresh(this._dirtyRowService.start, this._dirtyRowService.end);
-
-      if (Date.now() - startTime >= WRITE_TIMEOUT_MS) {
-        break;
-      }
-    }
-    if (this.writeBufferUtf8.length > bufferOffset) {
-      // Allow renderer to catch up before processing the next batch
-      // trim already processed chunks if we are above threshold
-      if (bufferOffset > WRITE_BUFFER_LENGTH_THRESHOLD) {
-        this.writeBufferUtf8 = this.writeBufferUtf8.slice(bufferOffset);
-        bufferOffset = 0;
-      }
-      setTimeout(() => this._innerWriteUtf8(bufferOffset), 0);
-    } else {
-      this._writeInProgress = false;
-      this.writeBufferUtf8 = [];
-    }
-  }
-
-  /**
-   * Writes text to the terminal.
-   * @param data The text to write to the terminal.
-   */
-  public write(data: string): void {
-    // Ensure the terminal isn't disposed
-    if (this._isDisposed) {
-      return;
-    }
-
-    // Ignore falsy data values (including the empty string)
-    if (!data) {
-      return;
-    }
-
-    this.writeBuffer.push(data);
-
-    // Send XOFF to pause the pty process if the write buffer becomes too large so
-    // xterm.js can catch up before more data is sent. This is necessary in order
-    // to keep signals such as ^C responsive.
-    if (this.options.useFlowControl && !this._xoffSentToCatchUp && this.writeBuffer.length >= WRITE_BUFFER_PAUSE_THRESHOLD) {
-      // XOFF - stop pty pipe
-      // XON will be triggered by emulator before processing data chunk
-      this._coreService.triggerDataEvent(C0.DC3);
-      this._xoffSentToCatchUp = true;
-    }
-
-    if (!this._writeInProgress && this.writeBuffer.length > 0) {
-      // Kick off a write which will write all data in sequence recursively
-      this._writeInProgress = true;
-      // Kick off an async innerWrite so more writes can come in while processing data
-      setTimeout(() => {
-        this._innerWrite();
-      });
-    }
-  }
-
-  protected _innerWrite(bufferOffset: number = 0): void {
-    // Ensure the terminal isn't disposed
-    if (this._isDisposed) {
-      this.writeBuffer = [];
-    }
-
-    const startTime = Date.now();
-    while (this.writeBuffer.length > bufferOffset) {
-      const data = this.writeBuffer[bufferOffset];
-      bufferOffset++;
-
-      // If XOFF was sent in order to catch up with the pty process, resume it if
-      // we reached the end of the writeBuffer to allow more data to come in.
-      if (this._xoffSentToCatchUp && this.writeBuffer.length === bufferOffset) {
-        this._coreService.triggerDataEvent(C0.DC1);
-        this._xoffSentToCatchUp = false;
-      }
-
-      this._inputHandler.parse(data);
-
-      this.refresh(this._dirtyRowService.start, this._dirtyRowService.end);
-
-      if (Date.now() - startTime >= WRITE_TIMEOUT_MS) {
-        break;
-      }
-    }
-    if (this.writeBuffer.length > bufferOffset) {
-      // Allow renderer to catch up before processing the next batch
-      // trim already processed chunks if we are above threshold
-      if (bufferOffset > WRITE_BUFFER_LENGTH_THRESHOLD) {
-        this.writeBuffer = this.writeBuffer.slice(bufferOffset);
-        bufferOffset = 0;
-      }
-      setTimeout(() => this._innerWrite(bufferOffset), 0);
-    } else {
-      this._writeInProgress = false;
-      this.writeBuffer = [];
-    }
-  }
-
-  /**
-   * Writes text to the terminal, followed by a break line character (\n).
-   * @param data The text to write to the terminal.
-   */
-  public writeln(data: string): void {
-    this.write(data + '\r\n');
-  }
-
   public paste(data: string): void {
     paste(data, this.textarea, this.bracketedPasteMode, this._coreService);
   }
@@ -1743,10 +1549,6 @@ export class Terminal extends Disposable implements ITerminal, IDisposable, IInp
     const customKeyEventHandler = this._customKeyEventHandler;
     const inputHandler = this._inputHandler;
     const cursorState = this.cursorState;
-    const writeBuffer = this.writeBuffer;
-    const writeBufferUtf8 = this.writeBufferUtf8;
-    const writeInProgress = this._writeInProgress;
-    const xoffSentToCatchUp = this._xoffSentToCatchUp;
     const userScrolling = this._userScrolling;
 
     this._setup();
@@ -1761,10 +1563,6 @@ export class Terminal extends Disposable implements ITerminal, IDisposable, IInp
     this._customKeyEventHandler = customKeyEventHandler;
     this._inputHandler = inputHandler;
     this.cursorState = cursorState;
-    this.writeBuffer = writeBuffer;
-    this.writeBufferUtf8 = writeBufferUtf8;
-    this._writeInProgress = writeInProgress;
-    this._xoffSentToCatchUp = xoffSentToCatchUp;
     this._userScrolling = userScrolling;
 
     // do a full screen refresh
@@ -1795,6 +1593,14 @@ export class Terminal extends Disposable implements ITerminal, IDisposable, IInp
     // return this.options.bellStyle === 'sound' ||
     //     this.options.bellStyle === 'both';
   }
+
+  public write(data: string | Uint8Array, callback?: () => void): void {
+    this._writeBuffer.write(data, callback);
+  }
+
+  public writeSync(data: string | Uint8Array): void {
+    this._writeBuffer.writeSync(data);
+  }
 }
 
 /**
diff --git a/src/TestUtils.test.ts b/src/TestUtils.test.ts
index ad19f7216a..a70f751c59 100644
--- a/src/TestUtils.test.ts
+++ b/src/TestUtils.test.ts
@@ -19,10 +19,6 @@ import { IParams, IFunctionIdentifier } from 'common/parser/Types';
 import { ISelectionService } from 'browser/services/Services';
 
 export class TestTerminal extends Terminal {
-  writeSync(data: string): void {
-    this.writeBuffer.push(data);
-    this._innerWrite();
-  }
   keyDown(ev: any): boolean { return this._keyDown(ev); }
   keyPress(ev: any): boolean { return this._keyPress(ev); }
 }
diff --git a/src/Types.d.ts b/src/Types.d.ts
index 13c65a4d69..cb45d3b1f2 100644
--- a/src/Types.d.ts
+++ b/src/Types.d.ts
@@ -73,8 +73,7 @@ export interface ICompositionHelper {
  * Calls the parser and handles actions generated by the parser.
  */
 export interface IInputHandler {
-  parse(data: string): void;
-  parseUtf8(data: Uint8Array): void;
+  parse(data: string | Uint8Array): void;
   print(data: Uint32Array, start: number, end: number): void;
 
   /** C0 BEL */ bell(): void;
@@ -151,7 +150,6 @@ export interface IInputHandler {
 export interface ITerminal extends IPublicTerminal, IElementAccessor, IBufferAccessor, ILinkifierAccessor {
   screenElement: HTMLElement;
   browser: IBrowser;
-  writeBuffer: string[];
   cursorHidden: boolean;
   cursorState: number;
   buffer: IBuffer;
@@ -192,7 +190,6 @@ export interface IPublicTerminal extends IDisposable {
   blur(): void;
   focus(): void;
   resize(columns: number, rows: number): void;
-  writeln(data: string): void;
   open(parent: HTMLElement): void;
   attachCustomKeyEventHandler(customKeyEventHandler: (event: KeyboardEvent) => boolean): void;
   addCsiHandler(id: IFunctionIdentifier, callback: (params: IParams) => boolean): IDisposable;
@@ -218,8 +215,7 @@ export interface IPublicTerminal extends IDisposable {
   scrollToBottom(): void;
   scrollToLine(line: number): void;
   clear(): void;
-  write(data: string): void;
-  writeUtf8(data: Uint8Array): void;
+  write(data: string | Uint8Array, callback?: () => void): void;
   paste(data: string): void;
   refresh(start: number, end: number): void;
   reset(): void;
diff --git a/src/common/input/WriteBuffer.test.ts b/src/common/input/WriteBuffer.test.ts
new file mode 100644
index 0000000000..ab9433da7e
--- /dev/null
+++ b/src/common/input/WriteBuffer.test.ts
@@ -0,0 +1,88 @@
+/**
+ * Copyright (c) 2019 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { assert } from 'chai';
+import { WriteBuffer } from './WriteBuffer';
+
+declare let Buffer: any;
+
+function toBytes(s: string): Uint8Array {
+  return Buffer.from(s);
+}
+
+function fromBytes(bytes: Uint8Array): string {
+  return bytes.toString();
+}
+
+describe('WriteBuffer', () => {
+  let wb: WriteBuffer;
+  let stack: (string | Uint8Array)[] = [];
+  let cbStack: string[] = [];
+  beforeEach(() => {
+    stack = [];
+    cbStack = [];
+    wb = new WriteBuffer(data => { stack.push(data); });
+  });
+  describe('write input', () => {
+    it('string', done => {
+      wb.write('a._');
+      wb.write('b.x', () => { cbStack.push('b'); });
+      wb.write('c._');
+      wb.write('d.x', () => { cbStack.push('d'); });
+      wb.write('e', () => {
+        assert.deepEqual(stack, ['a._', 'b.x', 'c._', 'd.x', 'e']);
+        assert.deepEqual(cbStack, ['b', 'd']);
+        done();
+      });
+    });
+    it('bytes', done => {
+      wb.write(toBytes('a._'));
+      wb.write(toBytes('b.x'), () => { cbStack.push('b'); });
+      wb.write(toBytes('c._'));
+      wb.write(toBytes('d.x'), () => { cbStack.push('d'); });
+      wb.write(toBytes('e'), () => {
+        assert.deepEqual(stack.map(val => typeof val === 'string' ? '' :  fromBytes(val)), ['a._', 'b.x', 'c._', 'd.x', 'e']);
+        assert.deepEqual(cbStack, ['b', 'd']);
+        done();
+      });
+    });
+    it('string/bytes mixed', done => {
+      wb.write('a._');
+      wb.write('b.x', () => { cbStack.push('b'); });
+      wb.write(toBytes('c._'));
+      wb.write(toBytes('d.x'), () => { cbStack.push('d'); });
+      wb.write(toBytes('e'), () => {
+        assert.deepEqual(stack.map(val => typeof val === 'string' ? val :  fromBytes(val)), ['a._', 'b.x', 'c._', 'd.x', 'e']);
+        assert.deepEqual(cbStack, ['b', 'd']);
+        done();
+      });
+    });
+    it('write callback works for empty chunks', done => {
+      wb.write('a', () => { cbStack.push('a'); });
+      wb.write('', () => { cbStack.push('b'); });
+      wb.write(toBytes('c'), () => { cbStack.push('c'); });
+      wb.write(new Uint8Array(0), () => { cbStack.push('d'); });
+      wb.write('e', () => {
+        assert.deepEqual(stack.map(val => typeof val === 'string' ? val :  fromBytes(val)), ['a', '', 'c', '', 'e']);
+        assert.deepEqual(cbStack, ['a', 'b', 'c', 'd']);
+        done();
+      });
+    });
+    it('writeSync', done => {
+      wb.write('a', () => { cbStack.push('a'); });
+      wb.write('b', () => { cbStack.push('b'); });
+      wb.write('c', () => { cbStack.push('c'); });
+      wb.writeSync('d');
+      assert.deepEqual(stack, ['a', 'b', 'c', 'd']);
+      assert.deepEqual(cbStack, ['a', 'b', 'c']);
+      wb.write('x', () => { cbStack.push('x'); });
+      wb.write('', () => {
+        assert.deepEqual(stack, ['a', 'b', 'c', 'd', 'x', '']);
+        assert.deepEqual(cbStack, ['a', 'b', 'c', 'x']);
+        done();
+      });
+    });
+  });
+});
diff --git a/src/common/input/WriteBuffer.ts b/src/common/input/WriteBuffer.ts
new file mode 100644
index 0000000000..c7d824585d
--- /dev/null
+++ b/src/common/input/WriteBuffer.ts
@@ -0,0 +1,110 @@
+
+/**
+ * Copyright (c) 2019 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+declare const setTimeout: (handler: () => void, timeout?: number) => void;
+
+/**
+ * Safety watermark to avoid memory exhaustion and browser engine crash on fast data input.
+ * Enable flow control to avoid this limit and make sure that your backend correctly
+ * propagates this to the underlying pty. (see docs for further instructions)
+ * Since this limit is meant as a safety parachute to prevent browser crashs,
+ * it is set to a very high number. Typically xterm.js gets unresponsive with
+ * a 100 times lower number (>500 kB).
+ */
+const DISCARD_WATERMARK = 50000000; // ~50 MB
+
+/**
+ * The max number of ms to spend on writes before allowing the renderer to
+ * catch up with a 0ms setTimeout. A value of < 33 to keep us close to
+ * 30fps, and a value of < 16 to try to run at 60fps. Of course, the real FPS
+ * depends on the time it takes for the renderer to draw the frame.
+ */
+const WRITE_TIMEOUT_MS = 12;
+
+/**
+ * Threshold of max held chunks in the write buffer, that were already processed.
+ * This is a tradeoff between extensive write buffer shifts (bad runtime) and high
+ * memory consumption by data thats not used anymore.
+ */
+const WRITE_BUFFER_LENGTH_THRESHOLD = 50;
+
+export class WriteBuffer {
+  private _writeBuffer: (string | Uint8Array)[] = [];
+  private _callbacks: ((() => void) | undefined)[] = [];
+  private _pendingData = 0;
+  private _bufferOffset = 0;
+
+  constructor(private _action: (data: string | Uint8Array) => void) { }
+
+  public writeSync(data: string | Uint8Array): void {
+    // force sync processing on pending data chunks to avoid in-band data scrambling
+    // does the same as innerWrite but without event loop
+    if (this._writeBuffer.length) {
+      for (let i = this._bufferOffset; i < this._writeBuffer.length; ++i) {
+        const data = this._writeBuffer[i];
+        const cb = this._callbacks[i];
+        this._action(data);
+        if (cb) cb();
+      }
+      // reset all to avoid reprocessing of chunks with scheduled innerWrite call
+      this._writeBuffer = [];
+      this._callbacks = [];
+      this._pendingData = 0;
+      // stop scheduled innerWrite by offset > length condition
+      this._bufferOffset = 0x7FFFFFFF;
+    }
+    // handle current data chunk
+    this._action(data);
+  }
+
+  public write(data: string | Uint8Array, callback?: () => void): void {
+    if (this._pendingData > DISCARD_WATERMARK) {
+      throw new Error('write data discarded, use flow control to avoid losing data');
+    }
+
+    // schedule chunk processing for next event loop run
+    if (!this._writeBuffer.length) {
+      this._bufferOffset = 0;
+      setTimeout(() => this._innerWrite());
+    }
+
+    this._pendingData += data.length;
+    this._writeBuffer.push(data);
+    this._callbacks.push(callback);
+  }
+
+  protected _innerWrite(): void {
+    const startTime = Date.now();
+    while (this._writeBuffer.length > this._bufferOffset) {
+      const data = this._writeBuffer[this._bufferOffset];
+      const cb = this._callbacks[this._bufferOffset];
+      this._bufferOffset++;
+
+      this._action(data);
+      this._pendingData -= data.length;
+      if (cb) cb();
+
+      if (Date.now() - startTime >= WRITE_TIMEOUT_MS) {
+        break;
+      }
+    }
+    if (this._writeBuffer.length > this._bufferOffset) {
+      // Allow renderer to catch up before processing the next batch
+      // trim already processed chunks if we are above threshold
+      if (this._bufferOffset > WRITE_BUFFER_LENGTH_THRESHOLD) {
+        this._writeBuffer = this._writeBuffer.slice(this._bufferOffset);
+        this._callbacks = this._callbacks.slice(this._bufferOffset);
+        this._bufferOffset = 0;
+      }
+      setTimeout(() => this._innerWrite(), 0);
+    } else {
+      this._writeBuffer = [];
+      this._callbacks = [];
+      this._pendingData = 0;
+      this._bufferOffset = 0;
+    }
+  }
+}
diff --git a/src/public/Terminal.ts b/src/public/Terminal.ts
index 6d6cedcacb..b8a70ff7e9 100644
--- a/src/public/Terminal.ts
+++ b/src/public/Terminal.ts
@@ -55,9 +55,6 @@ export class Terminal implements ITerminalApi {
     this._verifyIntegers(columns, rows);
     this._core.resize(columns, rows);
   }
-  public writeln(data: string): void {
-    this._core.writeln(data);
-  }
   public open(parent: HTMLElement): void {
     this._core.open(parent);
   }
@@ -128,11 +125,15 @@ export class Terminal implements ITerminalApi {
   public clear(): void {
     this._core.clear();
   }
-  public write(data: string): void {
-    this._core.write(data);
+  public write(data: string | Uint8Array, callback?: () => void): void {
+    this._core.write(data, callback);
   }
-  public writeUtf8(data: Uint8Array): void {
-    this._core.writeUtf8(data);
+  public writeUtf8(data: Uint8Array, callback?: () => void): void {
+    this._core.write(data, callback);
+  }
+  public writeln(data: string | Uint8Array, callback?: () => void): void {
+    this._core.write(data);
+    this._core.write('\r\n', callback);
   }
   public paste(data: string): void {
     this._core.paste(data);
diff --git a/test/api/Terminal.api.ts b/test/api/Terminal.api.ts
index b2157b1efc..034b04c496 100644
--- a/test/api/Terminal.api.ts
+++ b/test/api/Terminal.api.ts
@@ -51,6 +51,44 @@ describe('API Integration Tests', function(): void {
     assert.equal(await page.evaluate(`window.term.buffer.getLine(0).translateToString(true)`), 'foobar文');
   });
 
+  it('write with callback', async function(): Promise<any> {
+    await openTerminal();
+    await page.evaluate(`
+      window.term.write('foo', () => { window.__x = 'a'; });
+      window.term.write('bar', () => { window.__x += 'b'; });
+      window.term.write('文', () => { window.__x += 'c'; });
+    `);
+    assert.equal(await page.evaluate(`window.term.buffer.getLine(0).translateToString(true)`), 'foobar文');
+    assert.equal(await page.evaluate(`window.__x`), 'abc');
+  });
+
+  it('write - bytes (UTF8)', async function(): Promise<any> {
+    await openTerminal();
+    await page.evaluate(`
+      // foo
+      window.term.write(new Uint8Array([102, 111, 111]));
+      // bar
+      window.term.write(new Uint8Array([98, 97, 114]));
+      // 文
+      window.term.write(new Uint8Array([230, 150, 135]));
+    `);
+    assert.equal(await page.evaluate(`window.term.buffer.getLine(0).translateToString(true)`), 'foobar文');
+  });
+
+  it('write - bytes (UTF8) with callback', async function(): Promise<any> {
+    await openTerminal();
+    await page.evaluate(`
+      // foo
+      window.term.write(new Uint8Array([102, 111, 111]), () => { window.__x = 'A'; });
+      // bar
+      window.term.write(new Uint8Array([98, 97, 114]), () => { window.__x += 'B'; });
+      // 文
+      window.term.write(new Uint8Array([230, 150, 135]), () => { window.__x += 'C'; });
+    `);
+    assert.equal(await page.evaluate(`window.term.buffer.getLine(0).translateToString(true)`), 'foobar文');
+    assert.equal(await page.evaluate(`window.__x`), 'ABC');
+  });
+
   it('writeln', async function(): Promise<any> {
     await openTerminal();
     await page.evaluate(`
@@ -63,17 +101,29 @@ describe('API Integration Tests', function(): void {
     assert.equal(await page.evaluate(`window.term.buffer.getLine(2).translateToString(true)`), '文');
   });
 
-  it('writeUtf8', async function(): Promise<any> {
+  it('writeln with callback', async function(): Promise<any> {
     await openTerminal();
     await page.evaluate(`
-      // foo
-      window.term.writeUtf8(new Uint8Array([102, 111, 111]));
-      // bar
-      window.term.writeUtf8(new Uint8Array([98, 97, 114]));
-      // 文
-      window.term.writeUtf8(new Uint8Array([230, 150, 135]));
+      window.term.writeln('foo', () => { window.__x = '1'; });
+      window.term.writeln('bar', () => { window.__x += '2'; });
+      window.term.writeln('文', () => { window.__x += '3'; });
     `);
-    assert.equal(await page.evaluate(`window.term.buffer.getLine(0).translateToString(true)`), 'foobar文');
+    assert.equal(await page.evaluate(`window.term.buffer.getLine(0).translateToString(true)`), 'foo');
+    assert.equal(await page.evaluate(`window.term.buffer.getLine(1).translateToString(true)`), 'bar');
+    assert.equal(await page.evaluate(`window.term.buffer.getLine(2).translateToString(true)`), '文');
+    assert.equal(await page.evaluate(`window.__x`), '123');
+  });
+
+  it('writeln - bytes (UTF8)', async function(): Promise<any> {
+    await openTerminal();
+    await page.evaluate(`
+      window.term.writeln(new Uint8Array([102, 111, 111]));
+      window.term.writeln(new Uint8Array([98, 97, 114]));
+      window.term.writeln(new Uint8Array([230, 150, 135]));
+    `);
+    assert.equal(await page.evaluate(`window.term.buffer.getLine(0).translateToString(true)`), 'foo');
+    assert.equal(await page.evaluate(`window.term.buffer.getLine(1).translateToString(true)`), 'bar');
+    assert.equal(await page.evaluate(`window.term.buffer.getLine(2).translateToString(true)`), '文');
   });
 
   it('paste', async function(): Promise<any> {
@@ -83,11 +133,9 @@ describe('API Integration Tests', function(): void {
       window.term.onData(e => calls.push(e));
       window.term.paste('foo');
       window.term.paste('\\r\\nfoo\\nbar\\r');
-      window.term.write('\\x1b[?2004h');
-      // TODO: Use promise/callback for write when we support that
-      // Force sync write
-      window.term._core._innerWrite();
-      window.term.paste('foo');
+      window.term.write('\\x1b[?2004h', () => {
+        window.term.paste('foo');
+      });
     `);
     assert.deepEqual(await page.evaluate(`window.calls`), ['foo', '\rfoo\rbar\r', '\x1b[200~foo\x1b[201~']);
   });
diff --git a/test/benchmark/Terminal.benchmark.ts b/test/benchmark/Terminal.benchmark.ts
index a0b8fd298c..71a36cc70a 100644
--- a/test/benchmark/Terminal.benchmark.ts
+++ b/test/benchmark/Terminal.benchmark.ts
@@ -9,17 +9,6 @@ import { spawn } from 'node-pty';
 import { Utf8ToUtf32, stringFromCodePoint } from 'common/input/TextDecoder';
 import { Terminal } from 'Terminal';
 
-class TestTerminal extends Terminal {
-  writeSync(data: string): void {
-    this.writeBuffer.push(data);
-    this._innerWrite();
-  }
-  writeSyncUtf8(data: Uint8Array): void {
-    this.writeBufferUtf8.push(data);
-    this._innerWriteUtf8();
-  }
-}
-
 perfContext('Terminal: ls -lR /usr/lib', () => {
   let content = '';
   let contentUtf8: Uint8Array;
@@ -56,9 +45,9 @@ perfContext('Terminal: ls -lR /usr/lib', () => {
   });
 
   perfContext('write', () => {
-    let terminal: TestTerminal;
+    let terminal: Terminal;
     before(() => {
-      terminal = new TestTerminal({cols: 80, rows: 25, scrollback: 1000});
+      terminal = new Terminal({cols: 80, rows: 25, scrollback: 1000});
     });
     new ThroughputRuntimeCase('', () => {
       terminal.writeSync(content);
@@ -67,12 +56,12 @@ perfContext('Terminal: ls -lR /usr/lib', () => {
   });
 
   perfContext('writeUtf8', () => {
-    let terminal: TestTerminal;
+    let terminal: Terminal;
     before(() => {
-      terminal = new TestTerminal({cols: 80, rows: 25, scrollback: 1000});
+      terminal = new Terminal({cols: 80, rows: 25, scrollback: 1000});
     });
     new ThroughputRuntimeCase('', () => {
-      terminal.writeSyncUtf8(contentUtf8);
+      terminal.writeSync(content);
       return {payloadSize: contentUtf8.length};
     }, {fork: false}).showAverageThroughput();
   });
diff --git a/typings/xterm.d.ts b/typings/xterm.d.ts
index d0a33cbabe..44ef66bda1 100644
--- a/typings/xterm.d.ts
+++ b/typings/xterm.d.ts
@@ -650,24 +650,32 @@ declare module 'xterm' {
     clear(): void;
 
     /**
-     * Writes text to the terminal.
-     * @param data The text to write to the terminal.
+     * Write data to the terminal.
+     * @param data The data to write to the terminal. This can either be raw
+     * bytes given as Uint8Array from the pty or a string. Raw bytes will always
+     * be treated as UTF-8 encoded, string data as UTF-16.
+     * @param callback Optional callback that fires when the data was processed
+     * by the parser.
      */
-    write(data: string): void;
+    write(data: string | Uint8Array, callback?: () => void): void;
 
     /**
-     * Writes text to the terminal, followed by a break line character (\n).
-     * @param data The text to write to the terminal.
+     * Writes data to the terminal, followed by a break line character (\n).
+     * @param data The data to write to the terminal. This can either be raw
+     * bytes given as Uint8Array from the pty or a string. Raw bytes will always
+     * be treated as UTF-8 encoded, string data as UTF-16.
+     * @param callback Optional callback that fires when the data was processed
+     * by the parser.
      */
-    writeln(data: string): void;
+    writeln(data: string | Uint8Array, callback?: () => void): void;
 
     /**
-     * Writes UTF8 data to the terminal. This has a slight performance advantage
-     * over the string based write method due to lesser data conversions needed
-     * on the way from the pty to xterm.js.
+     * Write UTF8 data to the terminal.
      * @param data The data to write to the terminal.
+     * @param callback Optional callback when data was processed.
+     * @deprecated use `write` instead
      */
-    writeUtf8(data: Uint8Array): void;
+    writeUtf8(data: Uint8Array, callback?: () => void): void;
 
     /**
      * Writes text to the terminal, performing the necessary transformations for pasted text.