2.2: Data Storage Sizes
- Page ID
- 19863
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The x86-64 architecture supports a specific set of data storage size elements, all based on powers of two. The supported storage sizes are as follows:
| Storage | Size (bits) | Size (bytes) |
|---|---|---|
| Byte | 8-bits | 1 byte |
| Word | 16-bits | 2 bytes |
| Double-word | 32-bits | 4 bytes |
| Quadword | 64-bits | 8 bytes |
| Double quadword | 128-bits | 16 bytes |
Lists or arrays (sets of memory) can be reserved in any of these types.
These storage sizes have a direct correlation to variable declarations in high-level languages (e.g., C, C++, Java, etc.).
| C/C++ Declaration | Storage | Size (bits) | Size (bytes) |
|---|---|---|---|
| CHAR | Byte | 8-bits | 1 byte |
| short | Word | 16-bits | 2 bytes |
| int | Double-word | 32-bits | 4 bytes |
| unsigned int | Double-word | 32-bits | 4 bytes |
| long(Note, the 'long' type declaration is compiler dependent. Type shown is for gcc and g++ compilers.) | Quadword | 64-bits | 8 bytes |
| long long | Quadword | 64-bits | 8 bytes |
| char * | Quadword | 64-bits | 8 bytes |
| int * | Quadword | 64-bits | 8 bytes |
| float | Double-word | 32-bits | 4 bytes |
| double | Quadword | 64-bits | 8 bytes |
The asterisk indicates an address variable. For example, int * means the address of an integer. Other high-level languages typically have similar mappings.