---
description: "Learn more about: __m128d"
title: "__m128d"
ms.date: "11/04/2016"
f1_keywords: ["__m128d_cpp"]
helpviewer_keywords: ["__m128d keyword [C++]"]
ms.assetid: 8082c7c0-a955-4b53-9d82-9bb91c623f72
---
# __m128d

**Microsoft Specific**

The **`__m128d`** data type, for use with the Streaming SIMD Extensions 2 instructions intrinsics, is defined in \<emmintrin.h>.

```cpp
// data_types__m128d.cpp
#include <emmintrin.h>
int main() {
   __m128d x;
}
```

## Remarks

You should not access the **`__m128d`** 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 **_m128d** are automatically aligned on 16-byte boundaries.

The **`__m128d`** 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)