The document discusses the concept of endianness, which refers to the order of bytes in multi-byte data types across different computer architectures, specifically little-endian and big-endian systems. It highlights the issues that arise when data is shared between systems with different endianness, emphasizing the importance of proper byte order during data transmission and processing. Additionally, it mentions how certain CPUs may support switchable endianness and provides guidelines for handling byte order conversions in networking protocols.

1. Abstract
Computers speak different languages, like people. Some write
data "left-to-right" and others "right-to-left". If a machine can
read its own data it tends to encounter no problems but when
one computer stores data and a different type tries to read it,
that is when a problem occurs. This document aims to present
how Endianness is willing to be taken into consideration how
Endian specific system inter-operate sharing data without
misinterpretation of the value. Endianness describes the
location of the most significant byte (MSB) and least significant
byte (LSB) of an address in memory and is defined by the CPU
architecture implementation of the system. Unfortunately, not
all computer systems are designed with constant Endian
architecture. The difference in Endian architecture is a
difficulty when software or data is shared between computer
systems. Little and big endian are two ways of storing multibyte
data- type (int, float, etc.). In little endian machines, last byte
of binary representation of the multi byte data- type is stored
first. On the opposite hand, in big endian machines, first byte of
binary representation of the multi byte datatype is stored first.
Suppose we write float value to a file on a little-endian machine
and transfer this file to a big-endian machine. Unless there is
correct transformation, big endian machine will read the file in
reverse order. This paper targets on showcasing how CPU-based
Endianness raises software issues when reading and writing the
data from memory. We will try to reinterpret this information at
register/system-level.
Keywords: -
endianness, big-endian, little-endian, most significant byte

2. (MSB), least significant byte (LSB).
Definition of Endianness
: -
Endianness refers to order of bits or bytes within a binary
representation of a number. All computers do not store multi-
byte value in the same order. The difference in Endian
architecture is an issue when software or data is shared between
computer systems. An analysis of the computer system and its
interfaces will determine the requirements of the Endian
implementation of the software. Based on which value is stored
first, Endianness can be either big or small, with the adjectives
referring to which value is stored first.
Little Endian and Big Endian: -
Endianness illustrates how a 32-bit pattern is held in the four
bytes of memory. There are 32 bits in four bytes and 32 bits in
the pattern, but a choice has to be made about which byte of
memory gets what part of the pattern. There are two ways that
computers commonly do this.
Little endian and Big endian are the two ways of storing
multibyte data types. Little Endian and Big Endian are also
called host byte order and network byte order respectively. In a
multibyte data type, right most byte is called least significant
byte (LSB) and left most byte is called most significant byte
(MSB). In little endian the least significant byte is stored first,
while in big endian, most significant byte is stored. For
example, if we have store 0x01234567, then big and little
endian will be stored as below:
However, within a byte the order of the bits is the same for all
computers, no matter how the bytes themselves are arranged.

3. Bi -Endian: -
Some architectures such as ARM versions 3 and above, MIPS,
PA-RISC, etc. feature a setting which allows for switchable
endianness in data fetches and stores, instruction fetches, or
both. This feature can improve performance or simplify the
logic of networking devices and software. The word bi-endian,
when said of hardware, denotes the capability of the machine to
compute or pass data in either endian format.
Importance of endianness
:
Endianness is the attribute of a system that indicates whether
the data type like integer values are represented from left to
right or vice-versa. Endianness must be chosen every time
hardware or software is designed.
When Endianness affects code:
Endianness doesn’t apply to everything. If you do bitwise or
bit-shift operations on an int, you don’t notice endianness.
However, when data from one computer is used on another you
need to be concerned. For example, you have a file of integer
data that was written by another computer. To read it correctly,
you need to know:
· The number of bits used to represent each integer.
· The representational scheme used to represent integers (two's
complement or other).
· Which byte ordering (little or big endian) was used.
Processors Endianness
:

4. CPU controls the endianness. A CPU is instructed at boot time
to order memory as either big or little endian A few CPUs can
switch between big-endian and little-endian. However,
x86/amd64 architectures don't possess this feature. Computer
processors store data in either large (big) or small (little) endian
format depending on the CPU processor architecture. The
Operating System (OS) does not factor into the endianness of
the system, rather the endian model of the CPU architecture
dictates how the operating system is implemented. Big endian
byte ordering is considered the standard or neutral "Network
Byte Order". Big endian byte ordering is in a suitable format for
human interpretation and is also the order most often presented
by hex calculators. As most embedded communication
processors and custom solutions associated with the data plane
are Big-Endian (i.e. PowerPC, SPARC, etc.), the legacy code on
these processors is often written specifically for network byte
order (Big-Endian).
Few of the processors with their respective endianness’s are
listed below: -
Processor
Endianness
Motorola 68000
Big Endian

5. PowerPC (PPC)
Big Endian
Sun Sparc
Big Endian
IBM S/390
Big Endian
Intel x86 (32 bit)
Little Endian
Intel x86_64 (64 bit)
Little Endian

6. Dec VAX
Little Endian
Alpha
Bi (Big/Little) Endian
ARM
Bi (Big/Little) Endian
IA-64 (64 bit)
Bi (Big/Little) Endian
MIPS
Bi (Big/Little) Endian
Bi-Endian processors can be run in either mode, but only one
mode can be chosen for operation, there is no bi-endian byte

7. order. Byte order is either big or little endian.
Performance analysis
:
Endianness refers to data types that are stored differently in
memory, which means there are considerations when accessing
individual byte locations of a multi-byte data element in
memory.
Little-endian processors
have an advantage in cases where the memory bandwidth is
limited, like in some 32-bit ARM processors with 16-bit
memory bus, or the 8088 with 8-bit data bus. The processor can
just load the low half and complete add/sub/multiplication with
it while waiting for the higher half. With big-endian order when
we increase a numeric value, we add digits to the left (a higher
non-exponential number has more digits). Thus, an addition of
two numbers often requires moving all the digits of a big-endian
ordered number in storage, to the right. However, in a number
stored in little-endian fashion, the least significant bytes can
stay where they are, and new digits can be added to the right at
a higher address. Thus, resulting in some simpler and faster
computer operation.
Similarly, when we add or subtract multi-byte numbers, we need
to start with the least significant byte. If we are adding two 16-
bit numbers, there may be a carry from the least significant byte
to the most significant byte, so we must start with the least
significant byte to see if there is a carry. Therefore, we start
with the rightmost digit when doing longhand addition and not
from left. For example, consider an 8-bit system that fetches
bytes sequentially from memory. If it fetches the least
significant byte
first
, it can start doing the addition

8. while
the most significant byte is being fetched from memory. This
parallelism is why performance is better in little endian on such
as system. In case, it had to wait until both bytes were fetched
from memory, or fetch them in the reverse order, it would take
longer.
In
"Big-Endian" processor
, by having the high-order byte come first, we can quickly
analyze whether a number is positive or negative just by
looking at the byte at offset zero. We don't have to know how
long the number is, nor do you have to skip over any bytes to
find the byte containing the sign information. The numbers are
also stored in the order in which they are printed out, so binary
to decimal routines are highly efficient.
Handling
endianness automatically:-
To work automatically, network stacks and communication
protocols must also define their endianness, otherwise, two
nodes of different endianness won't be able to communicate.
Such a concept is termed as “Network Byte Order”. All protocol
layers in TCP/IP are defined to be big endian which is typically
called network byte order and that they send and receive the
most significant byte first.
If the computers at each end are little-endian, multi-byte
integers passed between them must be converted to network
byte order before transmission, across the network and
converted back to little-endian at the receiving end.
If the stack runs on a little-endian processor, it's to reorder, at
run time, the bytes of each multi-byte data field within the

9. various headers of the layers. If the stack runs on a big-endian
processor, there’s nothing to stress about. For the stack to be
portable, it's to choose to try and do this reordering, typically at
compile time.
To convert these conversions, sockets provides a collection of
macros to host a network byte order, as shown below:
• htons() - Host to network short, reorder the bytes of a 16-bit
unsigned value from processor order to network order.
• htonl() - Host to network long, reorder the bytes of a 32-bit
unsigned value from processor order to network order.
• ntohs() - Network to host short, reorder the bytes of a 16-bit
unsigned value from network order to processor order.
• ntohl() - Network to host long, reorder the bytes of a 32-bit
unsigned value from network order to processor order.
Let’s understand this with a better example:
Suppose there are two machines S1 and S2, S1 and S2 are big-
endian and little-endian relatively. If S1(BE) wants to send
0x44332211 to S2(LE)
• S1 has the quantity 0x44332211, it'll store in memory as
following sequence 44 33 22 11.
• S1 calls htonl () because the program has been written to be
portable. the quantity continues to be represented as 44 33 22
11 and sent over the network.
• S2 receives 44 33 22 11 and calls the ntohl().

10. • S2 gets the worth represented by 11 22 33 44 from ntohl(),
which then results to 0x44332211 as wanted.