Big-endian and little-endian are two different byte-ordering schemes used to represent multibyte data types, such as integers, in computer memory. These schemes determine the order in which bytes are stored in memory. The ARM architecture, like many other processor architectures, supports both big-endian and little-endian modes. Here’s an explanation of these concepts in the context of the ARM architecture:
Big-Endian:
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In a big-endian system, the most significant byte (MSB) of a multibyte data type is stored at the lowest memory address, and the least significant byte (LSB) is stored at the highest memory address.
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For example, consider the 32-bit hexadecimal number
0x12345678. In a big-endian system, it would be stored in memory as follows:Address: 0x1000 0x1001 0x1002 0x1003 Data: 0x12 0x34 0x56 0x78 -
Big-endian is a more human-readable format because the MSB comes first, similar to how we write numbers on paper.
Little-Endian:
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In a little-endian system, the least significant byte (LSB) of a multibyte data type is stored at the lowest memory address, and the most significant byte (MSB) is stored at the highest memory address.
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Using the same example (
0x12345678), it would be stored in memory as follows:Address: 0x1000 0x1001 0x1002 0x1003 Data: 0x78 0x56 0x34 0x12 -
Little-endian might seem counterintuitive at first glance because the bytes are stored in the reverse order compared to the human-readable representation.
ARM Architecture and Endianness:
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The ARM architecture supports both big-endian and little-endian modes, and the endianness can be configured at runtime for some ARM processors.
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ARMv8-A, the architecture for 64-bit ARM processors, supports both endiannesses, and the endianness can be selected independently for each execution state (AArch64 and AArch32).
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ARMv7-A, the architecture for 32-bit ARM processors, typically supports both endiannesses, but the specific support may depend on the implementation.
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Some ARM processors are designed to operate in a specific endianness mode, while others provide flexibility in choosing the endianness.
Considerations:
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Endianness can be relevant when data is shared between systems with different endianness, such as in networking or file formats.
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Most modern operating systems and applications are designed to be endianness-agnostic, meaning they can handle data in either endianness.
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Endianness becomes important in scenarios involving low-level memory manipulation, data serialization, and binary file formats.
The concept of big-endian and little-endian in the ARM architecture refers to the order in which bytes are stored in memory. The ARM architecture supports both endiannesses, and the choice of endianness may depend on the specific ARM processor implementation and configuration.