---
description: "Learn more about: __m128"
title: "__m128"
ms.date: "11/04/2016"
f1_keywords: ["__m128_cpp"]
helpviewer_keywords: ["__m128 keyword [C++]"]
ms.assetid: e51a472a-0e3c-4989-9a2a-36adb05273a3
---
# __m128

**Microsoft Specific**

The **__m128 data** type, for use with the Streaming SIMD Extensions and Streaming SIMD Extensions 2 instructions intrinsics, is defined in \<xmmintrin.h>.

```cpp
// data_types__m128.cpp
#include <xmmintrin.h>
int main() {
   __m128 x;
}
```

## Remarks

You should not access the **`__m128`** fields directly. You can, however, see these types in the debugger. A variable of type **`__m128`** maps to the XMM[0-7] registers.

Variables of type **`__m128`** are automatically aligned on 16-byte boundaries.

The **`__m128`** data type is not supported on ARM processors.

**END Microsoft Specific**

## See also

[Keywords](../cpp/keywords-cpp.md)<br/>
[Built-in types](../cpp/fundamental-types-cpp.md)<br/>
[Data Type Ranges](../cpp/data-type-ranges.md)