It describes the location of the most significant byte (MSB) and least significant byte (LSB) of an address in memory. "Endianness is the format to how multi-byte data is stored in computer memory. Intel gives the following definition of Endianness: In Big-Endian, Most-Significant-Byte (MSB) is stored at lowest address while, in Little-Endian, Least-Significant-Byte (LSB) is stored at lowest address. Thereby you can find out the endianness of your machine.īyte address | 0x01 | 0x02 | 0x03 | 0x04 |īyte content | 0x76 | 0x54 | 0x32 | 0x10 |īyte content | 0x10 | 0x32 | 0x54 | 0x76 | Now if you take a pointer c of type char and assign x's address to c by casting x to char pointer, then on little endian architecture you will get 0x10 when *c is printed and on big endian architecture you will get 0x76 while printing down *c. In big endian format the most significant byte is stored first, thus gets stored at the smallest address byte, while in little endian format the least significant byte is stored first.Īs an example, if x a four byte integer contains a hex value 0x76543210 ( '0x' stands for hex), the least significant byte will contain 0x10 and the most significant byte will store 0x76. In a multibyte data type such as int or long or any other multibyte data type the right most byte is called least significant byte and the left most byte is called most significant byte. These two formats are also called network byte order and host byte order respectively. The problem starts when computers store multibyte data, and question arises which byte should be stored at smallest address? Following is the way computers address this problem:īig endian and little endian are two formats to store multibyte data types into computer's memory. So do not get confused while handling single byte data. If it stores 0, the weight will be 2 3 * 0 = 0. The storage capacity of a bit is calculated by 2 sequence number * the value the bit stores.įor example, if the 3 rd bit of a byte stores 1 then its weight will be 2 3 * 1 = 8. Every bit carries a weight, which is its storage capacity. While, the left most bit is given sequence number 7 (seven), and it is called the most significant bit. The right most bit of a byte is given sequence number 0 (zero), and it is called least significant bit. Every bit in a byte is given a sequence number. One bit can store one of the two possible values either zero or one. Computers by different vendors agree upon some basic standards and the definition of byte. Then the address assigned to num will be 0x2100, and the value of expression &num yields 0x2100.Īnother important point to note that for single byte data endianness has no role to play. And second, the address assigned to the data object will be the smallest address of bytes allocated.įor example, if a data object num of type int takes four bytes in memory addressed as 0x2100, 0x2101, 0x2102, 0x2103. First, the data objects are allocated a contiguous sequence of bytes. Regardless of endianness (whether it is big or little endian) there are two common rules for data objects which take two or more bytes for storing information in memory. For example, a 32-bit word size computer can support up to 4GB virtual address space. That is, for a machine with an n-bit word size, the virtual address can range from 0 to 2 n - 1, giving the program access to at most 2 n bytes. The most important system parameter determined by the word size is the maximum size of the virtual address space. Further to bytes every computer has a word size, indicating the nominal size of integer and pointer data. Every byte of memory is recognized by a unique number, known as its address. And, memory to a program seems very large array of bytes. Because computers use blocks of eight bits (eight bits together form a byte), rather than accessing individual bits. To understand the terms little and big endian it might be useful to know the memory layout and architecture. Understanding Little Endian and Big Endian Architecture Little Endian and Big Endian Architecture.
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