CODEWITHSUNDEEP
javanetwork-programming
LoranceChen
LoranceChen

Reputation: 2574

Why java socket use Byte as base structure rather then Bit?

I writing a protocol use Bit to represent Boolean, but java network not use the smaller structure. I want to know why network data designed as byte rather then bit? expose atom structure isn't better?

Upvotes: 0

Views: 89

Answers (2)

jbm
jbm

Reputation: 3163

The network bandwidth saving that could be achieved by carrying single bits of payload, compared to the added complexity both at the hardware and software level, simply does not worth it.

Fundamentally, both at hardware level (registers) and software level, the minimal unit for data handling is byte, 8 bits (or octet, if you want to be nitpicking) or multiple of that. You cannot address memory at the bit level, only at the multiple of a byte level. Doing otherwise would be very complicated, down to the silicium level, without added value.

Whatever the programing language, when you declare and use a boolean, a byte (or a power of 2 multiple number of bytes, why not as long ass I can load it from memory to a CPU register) will actually be used to store it and the language will take care that only 2 cases when using it: is this byte all 0 bits, or not. At the machine code/assembly level: load this byte from its memory address to register FOO, or multiple bytes (if for example 32 bits wide register), cmp FOO to 0, depending on the result JE (Jump If Egal) to code address BAR, else go on with next machine code line. Or JNE (Jump if Not Equal) to such other code address. So your Javan boolean is not actually stored as a bit. It's, at minimum, a byte.

Even the good old Ethernet frame, not even looking at the actual useful payload, starts by a 56-bit preamble to synchronize devices. 56 bits is 7 bytes. Could the synchronization be done with less than that? Not a number of bytes? Maybe, but that does not worth the effort.

https://en.wikipedia.org/wiki/Ethernet_frame#Preamble_and_start_frame_delimiter

Pedantic edit for nitpickers:

A language such as C have a bit field facility:

https://en.wikipedia.org/wiki/Bit_field

...but don't be fooled, the minimal storage unit at the silicum level for a bit from a bit field will still be a byte. Hence the "field" in "bit fields".

Upvotes: 1

Raedwald
Raedwald

Reputation: 48682

Because the fundamental packets of IP are defined in terms of bytes rather than bits. All packets are a whole number of bytes rather than bits. Even bit fields are part of a multi-byte field. Bytes, rather than bits, are fundamental to IP.

This is ultimately because computer memory does not have addressable bits, but rather has addressable bytes. Any implementation of a networking protocol would have to be based on bytes, not bits. And that that is also why Java does not provide direct access to bits.

Upvotes: 2

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