Post: the origin of endian

From:

Http://www.eygle.com/digest/2007/01/whats_mean_endian.html

 

 

I. Introduction
In various computer architectures, the storage mechanisms for bytes and words are different, leading
A very important issue in the field of computer communication, that is, the information units (bit, byte,
Characters, double characters, etc.) in what order should be transmitted. If no agreement is reached, the communications Parties
Communication will fail due to the failure of correct encoding/decoding. Currently, in the computer of various systems
There are two main types of byte storage mechanisms used:
Big-edian and little-Endian. This article briefly describes the origins, features, and differences between the two storage mechanisms.

For the sake of convenience, the following briefly defines the two terms to be used in this article.
1. MSB
MSB is the abbreviation of most significant bit/byte.
Important bytes. It is usually used to indicate that in a bit sequence (for example, a byte is a sequence consisting of 8 bits)
Column) or a byte sequence (for example, word is a sequence composed of two bytes ).
The bit/byte with the largest impact.
2. LSB
LSB is the abbreviation of least significant bit/byte.
The least important byte. It is usually used to indicate that in a bit sequence (for example, a byte is composed of 8 bits)
A sequence) or a byte sequence (for example, word is a sequence composed of two bytes)
The bit/byte with the least impact on the column value.

Ii. Origins of endian
1. Definition
Endian: the ordering of bytes in a multi-byte number.
Definition: used to describe the storage order of each byte in the Multi-byte number in the computer system architecture.

2. Etymology
The term comes from Swift's "Gulliver's Travels" via the famous paper
"On holy wars and a plea for peace" by Danny Cohen, USC/ISI ien 137,
1980-04-01.
The Lilliputians, being very small, had correspondingly small political
Problems. The big-Endian and little-Endian parties debated over whether
Soft-boiled eggs shoshould be opened at the big end or the little end. [from:
Free on-line Dictionary of computing or jargon file]
Source: According to jargon file, the word endian comes from Jonathan
Swift wrote the ironic novel "Gulliver's Travels" in 1726. This novel
When describing Gulliver's Changyou Minor people's country, we encountered the following scenario. The villain in the country is very
Small (6 inch tall), so I always encounter unexpected problems. Once, because the boiled eggs should be big
The debate over whether one end (big-end) is stripped or a small end (little-end) leads to a war,
Two opposing teams were formed: Swift, the one that supports big-end exploitation, is called Big-endians.
The people who support Stripping from Little-end are called Little-endians ...... (The suffix Ian indicates support.
A certain point of view :-). The term endian comes from this.

In 1980, Danny Cohen published his paper "on holy wars and a plea for peace"
In order to calm down a debate about the order in which bytes should be transmitted in a message, the term is referenced.
In this article, Cohen refers to the group that supports message sequence transmission starting from MSB.
Big-endians, which is called Little-endians. After that, endian
And is widely used in this paper.

Iii. Various endian
1. Big-Endian
A computer architecture in which, within a given multi-byte numeric
Representation, the most significant byte has the lowest address (
Word is stored "big-end-First ").
Most processors, including the IBM 370 family, the PDP-10,
Motorola microprocessor families, and most of the various RISC Designs
Current in mid-1993, are big-Endian. [from: free on-line Dictionary
Computing or jargon file]
Big-Endian: a term in the computer architecture that describes the order of Multi-byte storage.
The most important byte (MSB) is stored on the lowest-end address. This mechanism is applicable to ibm3700 processors.
Columns, PDP-10, mortolora microprocessor series and the vast majority of RISC processors.

 

+ ---------- +
| 0x34 | <-- 0x00000021
+ ---------- +
| 0x12 | <-- 0x00000020
+ ---------- +
Figure 1: the double byte 0x1234 exists in the starting address 0x00000020 in the big-Endian Mode

In big-Endian, the sequence number in the bit sequence is organized as follows (with the double byte 0x8b8a
Example ):
Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+ ---------------------------------------- +
Val | 1 0 0 0 1 0 1 1 | 1 0 0 0 1 0 |
+ ---------------------------------------- +
^ 0x8b 0x8a ^
MSB LSB
Figure 2: bit sequence encoding method of big-Endian

Note 1: Generally, the network order in the TCP/IP protocol stack follows the big-Endian
Rules. In TCP/IP network communication, both parties encode the message in the form of 2, and then press
The sequence from MSB (bit0) to LSB is transmitted over the network.
2. Little-Endian
A computer architecture in which, within a given
16-or 32-bit word, bytes at lower addresses have lower significance (
Word is stored "Little-end-First"). The PDP-11 and VAX families
Computers and Intel microprocessors and a lot of communications and
Networking hardware are little-Endian.
The term is sometimes used to describe the ordering of Units other
Than bytes; most often, bits within a byte. [from: free on-line dictionary
Of computing or jargon file]
Little-Endian: a term in the computer architecture that describes the order of Multi-byte storage.
The least important byte (LSB) is stored on the lowest-end address. The processor using this mechanism has PDP-11,
Vax, Intel series microprocessor, and some network communication devices. In addition to describing the multi-byte storage sequence
It is often used to describe the emission sequence of each bit in a byte.

+ ---------- +
| 0x12 | <-- 0x00000021
+ ---------- +
| 0x34 | <-- 0x00000020
+ ---------- +
Figure 3: The Double Byte 0x1234 exists in the starting address 0x00000020 as little-endian

In little-Endian, sequence number Orchestration in bit sequence is the opposite of big-Endian.
Format ):

Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
+ ----------------------------------------- +
Val | 1 0 0 0 1 0 1 1 | 1 0 0 0 1 0 |
+ ----------------------------------------- +
^ 0x8b 0x8a ^
MSB LSB
Figure 4: bit sequence encoding method of little-Endian

NOTE 2: Generally, the host order follows the little-Endian rule. So
When the two hosts need to communicate through the TCP/IP protocol, they need to call the corresponding function for the host
The conversion between the order (little-Endian) and the network Order (big-Endian.
NOTE 3: because these two mechanisms have the opposite sequence number arrangement mode for the same bit sequence
The translation of MSB in the English-to-English dictionary is not proper. Therefore, this article defines it as "the most important bit
/Byte ".

3. Middle-Endian:
Neither big-Endian nor little-Endian. Used
Perverse byte orders such as 3-4-1-2 or 2-1-4-3, occasionally found in
The packed decimal formats of some minicomputer manufacturers. [from:
Free on-line Dictionary of computing or jargon file]
Middle-Endian: In addition to big-Endian and little-Endian, the multi-byte storage order is
For example, four bytes are used as an example.
It is middle-Endian. This storage order occasionally compresses the number of decimal digits in some minicomputers.
.
Iv. Final Stage
The two encoding sequences have exceeded the content in this article. If you are interested
To refer to Danny Cohen's paper ("On holy wars and a plea for peace "),
This paper describes in detail the history of these two encoding sequences, the mathematical theories based on and the arguments of their respective advocates.
The focus and other knowledge can definitely satisfy your inner needs.

V. References & weblinks
1. free on-line Dictionary of Computing
[Http://foldoc.doc.ic.ac.uk/foldoc/index.html]
2. jargon file [http://info.astrian.net/jargon/]
3. Gulliver's Travels garifo Travel Notes
[Http://www.jaffebros.com/lee/gulliver/]
4. On holy wars and a plea for peace

[Http://khavrinen.lcs.mit.edu/wollman/ien-137.txt]

 

 

 

Http://en.wikipedia.org/wiki/Endianness