维基百科上说
当需要对二进制数据进行编码时，通常使用Base64编码方案，这些数据需要通过设计用于处理文本数据的媒体存储和传输。这是为了确保数据在传输过程中保持完整而不被修改。
但是，数据不总是以二进制存储/传输吗?因为我们机器的内存存储二进制，这只是取决于你如何解释它?因此，无论您将位模式010011010110000101101110编码为ASCII中的Man还是Base64中的TWFu，最终都将存储相同的位模式。
如果最终的编码是用0和1表示的，并且每台机器和媒体都可以处理它们，那么数据是用ASCII还是Base64表示有什么关系呢?
“设计用于处理文本数据的媒体”是什么意思?他们可以处理二进制=>他们可以处理任何东西。
谢谢大家，我想我现在明白了。
当我们发送数据时，我们不能确定数据将以与我们预期的相同格式进行解释。因此，我们发送以双方都能理解的某种格式(如Base64)编码的数据。这样，即使发送方和接收方对相同内容的解释不同，但由于他们对编码格式达成一致，数据也不会被错误地解释。
来自Mark Byers的例子
如果我想发送
Hello
world!
一种方法是用ASCII码发送
72 101 108 108 111 10 119 111 114 108 100 33
但是字节10在另一端可能不能被正确地解释为换行符。因此，我们使用ASCII的一个子集来像这样编码
83 71 86 115 98 71 56 115 67 110 100 118 99 109 120 107 73 61 61
以传输相同数量信息的更多数据为代价，确保接收者能够以预期的方式解码数据，即使接收者对其余字符集有不同的解释。
为什么/如何使用Base64编码?
Base64 is one of the binary-to-text encoding scheme having 75% efficiency. It is used so that typical binary data (such as images) may be safely sent over legacy "not 8-bit clean" channels.
In earlier email networks (till early 1990s), most email messages were plain text in the 7-bit US-ASCII character set. So many early comm protocol standards were designed to work over "7-bit" comm links "not 8-bit clean".
Scheme efficiency is the ratio between number of bits in the input and the number of bits in the encoded output.
Hexadecimal (Base16) is also one of the binary-to-text encoding scheme with 50% efficiency.
Base64编码步骤(简化):
Binary data is arranged in continuous chunks of 24 bits (3 bytes) each.
Each 24 bits chunk is grouped in to four parts of 6 bit each.
Each 6 bit group is converted into their corresponding Base64 character values, i.e. Base64 encoding converts three octets into four encoded characters. The ratio of output bytes to input bytes is 4:3 (33% overhead).
Interestingly, the same characters will be encoded differently depending on their position within the three-octet group which is encoded to produce the four characters.
The receiver will have to reverse this process to recover the original message.
为什么不看看当前定义Base64的RFC呢?
Base encoding of data is used in
many situations to store or transfer
data in environments that, perhaps for
legacy reasons, are restricted to
US-ASCII [1] data.Base encoding can
also be used in new applications
that do not have legacy restrictions,
simply because it makes it possible
to manipulate objects with text
editors.
In the past, different applications
have had different requirements and
thus sometimes implemented base
encodings in slightly different
ways. Today, protocol specifications
sometimes use base encodings in
general, and "base64" in particular,
without a precise description or
reference. Multipurpose Internet Mail
Extensions (MIME) [4] is often used
as a reference for base64 without
considering the consequences for
line-wrapping or non-alphabet
characters. The purpose of this
specification is to establish common
alphabet and encoding
considerations. This will hopefully
reduce ambiguity in other
documents, leading to better
interoperability.
Base64最初被设计为一种允许二进制数据附加到电子邮件的方式，作为多用途互联网邮件扩展的一部分。
