What s the difference between a word and byte

Question

I ve done some research  A byte is 8 bits and a word is the smallest unit that can be addressed on memory  The exact length of a word varies  What I don t understand is what s the point of having a byte  Why not say 8 bits   I asked a prof this question and he said most machines these days are byte-addressable  but what would that make a word

User · Answer

The exact length of a word varies  What I don t understand is what s the point of having a byte  Why not say 8 bits    Even though the length of a word varies  on all modern machines and even all older architectures that I m familiar with  the word size is still a multiple of the byte size  So there is no particular downside to using  byte  over  8 bits  in relation to the variable word size   Beyond that  here are some reasons to use byte  or octet1  over  8 bits     Larger units are just convenient to avoid very large or very small numbers  you might as well ask  why say 3 nanoseconds when you could say 0 000000003 seconds  or  why say 1 kilogram when you could say 1 000 grams   etc  Beyond the convenience  the unit of a byte is somehow as fundamental as 1 bit since many operations typically work not at the byte level  but at the byte level  addressing memory  allocating dynamic storage  reading from a file or socket  etc  Even if you were to adopt  8 bit  as a type of unit  so you could say  two 8-bits  instead of  two bytes   it would be often be very confusing to have your new unit start with a number  For example  if someone said  one-hundred 8-bits  it could easily be interpreted as 108 bits  rather than 100 bits      1 Although I ll consider a byte to be 8 bits for this answer  this isn t universally true  on older machines a byte may have a different size  such as 6 bits  Octet always means 8 bits  regardless of the machine  so this term is often used in defining network protocols    In modern usage  byte is overwhelmingly used as synonymous with 8 bits

User · Answer

BYTE  I am trying to answer this question from C   perspective   The C   standard defines    byte    as    Addressable unit of data large enough to hold any member of the basic character set of the execution environment      What this means is that the byte consists of at least enough adjacent bits to accommodate the basic character set for the implementation  That is  the number of possible values must equal or exceed the number of distinct characters   In the United States  the basic character sets are usually the ASCII and EBCDIC sets  each of which can be accommodated by 8 bits  Hence it is guaranteed that a byte will have at least 8 bits   In other words  a byte is the amount of memory required to store a single character   If you want to verify    number of bits    in your C   implementation  check the file    limits h     It should have an entry like below    define CHAR BIT      8            number of bits in a char      WORD  A Word is defined as specific number of bits which can be processed together  i e  in one attempt  by the machine system  Alternatively  we can say that Word defines the amount of data that can be transferred between CPU and RAM in a single operation   The hardware registers in a computer machine are word sized   The Word size also defines the largest possible memory address  each memory address points to a byte sized memory    Note     In C   programs  the memory addresses points to a byte of memory and not to a word

User · Answer

Reference https   www os-book com OS9 slide-dir PPT-dir ch1 ppt   The basic unit of computer storage is the bit  A bit can contain one of two values  0 and 1  All other storage in a computer is based on collections of bits  Given enough bits  it is amazing how many things a computer can represent  numbers  letters  images  movies  sounds  documents  and programs  to name a few  A byte is 8 bits  and on most computers it is the smallest convenient chunk of storage  For example  most computers don   t have an instruction to move a bit but do have one to move a byte  A less common term is word  which is a given computer architecture   s native unit of data  A word is made up of one or more bytes  For example  a computer that has 64-bit registers and 64- bit memory addressing typically has 64-bit  8-byte  words  A computer executes many operations in its native word size rather than a byte at a time  Computer storage  along with most computer throughput  is generally measured and manipulated in bytes and collections of bytes  A kilobyte  or KB  is 1 024 bytes a megabyte  or MB  is 1 024 2 bytes a gigabyte  or GB  is 1 024 3 bytes a terabyte  or TB  is 1 024 4  bytes a petabyte  or PB  is 1 024 5 bytes Computer manufacturers often round off these numbers and say that a megabyte is 1 million bytes and a gigabyte is 1 billion bytes  Networking measurements are an exception to this general rule  they are given in bits  because networks move data a bit at a time

User · Answer

What I don t understand is what s the point of having a byte  Why not say 8 bits    Apart from the technical point that a byte isn t necessarily 8 bits  the reasons for having a term is simple human nature    economy of effort  aka laziness  - it is easier to say  byte  rather than  eight bits  tribalism - groups of people like to use jargon   a private language to set them apart from others    Just go with the flow   You are not going to change 50  years of accumulated IT terminology and cultural baggage by complaining about it     FWIW - the correct term to use when you mean  8 bits independent of the hardware architecture  is  octet

User · Answer

A group of 8 bits is called a byte   with the exception where it is not    for certain architectures    A word is a fixed sized group of bits that are handled as a unit by the instruction set and or hardware of the processor  That means the size of a general purpose register   which is generally more than a byte   is a word  In the C  a word is most often called an integer    int

User · Answer

In fact  in common usage  word has become synonymous with 16 bits  much like byte has with 8 bits   Can get a little confusing since the  word size  on a 32-bit CPU is 32-bits  but when talking about a word of data  one would mean 16-bits   Microcontrollers with a 32-bit word size have taken to calling their instructions  longs   supposedly to try and avoid the word doubleword confusion

User · Answer

In this context  a word is the unit that a machine uses when working with memory  For example  on a 32 bit machine  the word is 32 bits long and on a 64 bit is 64 bits long  The word size determines the address space   In programming  C C     the word is typically represented by the int ptr type  which has the same length as a pointer  this way abstracting these details   Some APIs might confuse you though  such as Win32 API  because it has types such as WORD  16 bits  and DWORD  32 bits   The reason is that the API was initially targeting 16 bit machines  then was ported to 32 bit machines  then to 64 bit machines  To store a pointer  you can use INT PTR  More details here and here

User · Answer

Whatever the terminology present in datasheets and compilers  a  Byte  is eight bits  Let s not try to confuse enquirers and generalities with the more obscure exceptions  particularly as the word  Byte  comes from the expression  By Eight   I ve worked in the semiconductor electronics industry for over thirty years and not once known  Byte  used to express anything more than eight bits

User · Answer

If a machine is byte-addressable and a word is the smallest unit that can be addressed on memory then I guess a word would be a byte

User · Answer

A word is the size of the registers in the processor  This means processor instructions like  add  mul  etc are on word-sized inputs   But most modern architectures have memory that is addressable in 8-bit chunks  so it is convenient to use the word  byte

User · Answer

Why not say 8 bits    Because not all machines have 8-bit bytes  Since you tagged this C  look up CHAR BIT in limits h

User · Answer

It seems all the answers assume high level languages and mainly C C      But the question is tagged  assembly  and in all assemblers I know  for 8bit  16bit  32bit and 64bit CPUs   the definitions are much more clear   byte    8 bits  word    2 bytes dword   4 bytes   2Words  dword means  double word   qword   8 bytes   2Dwords   4Words   quadruple word

User · Answer

Byte  Today  a byte is almost always 8 bit  However  that wasn t always the case and there s no  standard  or something that dictates this  Since 8 bits is a  convenient number to work with it became the de facto standard   Word  The natural size with which a processor is handling data  the register size   The most common word sizes encountered today are 8  16  32 and 64 bits  but other sizes are possible  For examples  there were a few 36 bit machines  or even 12 bit machines   The byte is the smallest addressable unit for a CPU  If you want to set clear single bits  you first need to fetch the corresponding byte from memory  mess with the bits and then write the byte back to memory   The word by contrast is biggest chunk of bits with which a processor can do processing  like addition and subtraction  at a time  That definition is a bit fuzzy  as some processor might have different word sizes for different tasks  integer vs  floating point processing for example   The word size is what the majority of operations work with   There are also a few processors who have a different pointer size  for example  the 8086 is a 16-bit processor which means its registers are 16 bit wide  But its pointers  addresses  are 20 bit wide and were calculated by combining two 16 bit registers in a certain way

User · Answer

The terms of BYTE and WORD are relative to the size of the processor that is being referred to  The most common processors are were 8 bit  16 bit  32 bit or 64 bit  These are the WORD lengths of the processor  Actually half of a WORD is a BYTE  whatever the numerical length is  Ready for this  half of a BYTE is a NIBBLE

[assembly] What's the difference between a word and byte?

Examples related to assembly

Examples related to memory

Examples related to hardware

Examples related to terminology

Examples related to cpu-architecture