Difference between Byte Addressable Memory and Word Addressable Memory

Memory is a storage component in the Computer used to store application programs. The Memory Chip is divided into equal parts called as “CELLS”. Each Cell is uniquely identified by a binary number called as “ADDRESS”. For example, the Memory Chip configuration is represented as ’64 K x 8′ as shown in the figure below. 

The following information can be obtained from the memory chip representation shown above: 

1. Data Space in the Chip = 64K X 8 
2. Data Space in the Cell = 8 bits 
3. Address Space in the Chip = \log_{2} (64 K)  =16 bits 

Now we can clearly state the difference between Byte Addressable Memory & Word Addressable Memory.

S. No.	Byte Addressable Memory	Word Addressable Memory
1.	When the data space in the cell = 8 bits then the corresponding address space is called as Byte Address.	When the data space in the cell = word length of CPU then the corresponding address space is called as Word Address.
2.	Based on this data storage i.e. Bytewise storage, the memory chip configuration is named as Byte Addressable Memory.	Based on this data storage i.e. Wordwise storage, the memory chip configuration is named as Word Addressable Memory.
3.	For eg. : 64K X 8 chip has 16 bit Address and cell size = 8 bits (1 Byte) which means that in this chip, data is stored byte by byte.	For eg. : For a 16-bit CPU, 64K X 16 chip has 16 bit Address & cell size = 16 bits (Word Length of CPU) which means that in this chip, data is stored word by word.
4.	It is suitable for the processes that require data comprising single byte at a time. A single address is issued for accessing a single byte in byte addressable memory.	In case of word addressable memory, the necessary condition involves computing the address of word that contains required byte, fetch that word and then extraction of needed byte from the two byte word takes place. So, it is indirectly accessible. Hence, modern machines are byte addressable.

NOTE :

i) The most important point to be noted is that in case of either of Byte Address or Word Address, the address size can be any number of bits (depends on the number of cells in the chip) but the cell size differs in each case. 

ii)The default memory configuration in the Computer design is Byte Addressable .

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