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{{Parent|Considerations for Multi-Device Applications}}

==The Extended Data Type Is 2 Bytes Smaller on 64-bit Windows Systems==
 
The size of the '''[[lib_en:System.Extended|Extended]]''' data type is different on Win64 and on Win32:
* On Win64, the '''Extended''' type is an alias for a '''[[lib_en:System.Double|Double]]''', or 8 bytes.
* On Win32, the '''Extended''' type is (still) 10 bytes.  
Thus you have less precision using an '''Extended''' data type on Win64 compared to Win32. If your applications use the '''Extended''' data type and you rely on precision, such as for floating-point operations, this size difference might affect your data. 

Very small or very large values are most affected. The precision of the two data types is as follows:
* 1x10<sup>308</sup> IEEE Double, supported by Win64
* 1x10<sup>4932</sup> IEEE Extended, supported by Win32

If your code base contains the '''Extended''' data type, you will receive the hint message: [[W1066 Lost Extended floating point precision. Reduced to Double (Delphi)]]. Extended precision floating-point operations are supported in the 32-bit applications and not supported in 64-bit applications. On Win64 the precision of floating-point operations with '''Extended''' variables is reduced to double precision.

The '''[[lib_en:System.TExtended80Rec|TExtended80Rec]]''' record can be used to work with extended precision floating-point variables, but only to read or write to and from the memory and to perform low-level changes (modifying the mantissa, exponent, or sign).

For more information about 64-bit data types, see [[64-bit Windows Data Types Compared to 32-bit Windows Data Types]].

== Stack Alignment Issue on OS X ==

For OS X applications, one big issue is the requirement that all memory data be stack-aligned on 16-byte boundaries: 
* For details, see Eli Boling's blog: http://blogs.embarcadero.com/eboling/2009/05/20/5607.  
* For {{Delphi}} applications, you can use the [[Code align ({{Delphi}})]] directive to set 16-byte boundaries. 
* Also see the ALIGN_STACK Define in [[Conditional compilation ({{Delphi}})]].

== Migrating {{Delphi}} Applications from Win32 to OS X ==
The following table summarizes the platform support by the various libraries in {{Variables|Product}}:

{| border="1" frame="hsides" rules="rows" style="text-align:center;"
! &nbsp;&nbsp;&nbsp;'''Library\Platform'''&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
! &nbsp;&nbsp;&nbsp;'''Win32'''&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
! &nbsp;&nbsp;&nbsp;'''Win64'''&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
! &nbsp;&nbsp;&nbsp;&nbsp;'''Mac OS X'''&nbsp;&nbsp;&nbsp;&nbsp;
|- valign="center"
|
'''FMX'''
|
Yes
|
Yes
|
Yes
|- valign="center"
|
'''RTL'''
|
Yes
|
Yes
|
Yes
|- valign="center"
| 
'''VCL'''
|
Yes
|
Yes
|
Not supported
|}

<blockquote>'''Note:''' The table above is only a high-level representation of library support for platforms. 

Some exceptions do exist in RTL and VCL support for specific platforms. {{f|bde|For example, BDE is not supported on either Win64 or Mac OS X.}} </blockquote>

The VCL is Windows-only, and does not support OS X. Applications that target OS X should be built with {{FM}} ([[lib_en:FMX|FMX]]).

The majority of the {{Delphi}} Run-Time Library (RTL), on the other hand, supports all the [[Supported Target Platforms]]. The RTL contains the System, SysUtils, and IOUtils units, and others, which contain platform-neutral elements.
* {{Delphi}} applications that use only the RTL (not the VCL) work on OS X (and Win64) with few changes.
* Any {{Delphi}} application that uses the VCL and/or the RTL supports both Win32 and Win64. 


For more information about the RTL, see [[Using the RTL (Run-Time Library)|Using the RTL (Run-Time Library)]].

For more information about {{FM}}, see [[FireMonkey]].

{{f|vcl|For More Information about the VCL, see [[Introducing the Visual Component Library (VCL)]].}}

== Migrating {{Delphi}} Applications from Win32 to Win64 ==
The VCL and the RTL are supported on both Win32 and Win64.

For {{Delphi}} Win64 application development, see [[64-bit Windows Application Development]].

== Migrating {{Delphi}} Applications from Desktop to Mobile ==

* [[Migrating Delphi Code to Mobile from Desktop]]
* [[Automatic Reference Counting in Delphi Mobile Compilers]]

== In Win64, 'absolute' Keyword is Not Supported in Interop between {{Delphi}} and {{CBuilder}}  ==
<!-- RS-51521 / 53523  -->
If you want to write {{Delphi}} code that runs interop with the [[Clang-enhanced C++ Compilers]], you cannot use the "absolute" {{Delphi}} directive/keyword in the '''interface''' section of a {{Delphi}} app when running interop with any of the [[Clang-enhanced C++ Compilers]]. However, you can use the "absolute" keyword  in the '''implementation''' section. 

LLVM does not offer the mechanism for a variable to overlay on another, so {{CBuilder}} assumes a unique symbol for each variable.

== Inline Assembly Limitations on 64-bit Windows ==
If your code base contains inline assembly code, you might need to make code changes in order to move to 64-bit. For more information, see the following topics:
* [[DCC64#64-bit Inline Assembler|64-bit {{Delphi}} Inline Assembler]]
** [[Using Inline Assembly Code]]
** [[Assembly Procedures and Functions ]]
* [[Converting 32-bit Delphi Applications to 64-bit Windows]]

==See Also==
* [[64-bit Windows Application Development]]
* [[C++ Considerations for Multi-Device Applications]]
* [[Differences between Windows and Mac OS X]]
* [[64-bit Windows Data Types Compared to 32-bit Windows Data Types]]

[[Category:XE2]][[Category:Multi-Device]]
[[Category:Floating-Point]]
[[Category:64Bit]]
[[Category:Mac OS X]]
 [[Category:AMMigrate]]

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