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by drewg123 3256 days ago
I fondly remember unaligned access faults "back in the day" with FreeBSD/alpha. We implemented a fixup for applications, but not for the kernel. I seem to recall that even though x86 could deal with unaligned accesses, it caused minor performance problems, so fixing alignment issues on alpha would benefit x86 as well.

Most (definitely not all) of the mis-alignment problems were in the network stack, and were centered around the fact that ethernet headers are 14 bytes, while nearly all other protocols had headers that were a multiple of at least 4 bytes.

I've said it before, and I'll say it again: If I had a time machine, I would not kill Hitler. I'd go back to the 70s and make the ethernet header be 16 bytes long, rather than 14.
1 comments
IgorPartola 3256 days ago
Why in god's name did they make it 14?!
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pjc50 3256 days ago
Ethernet was invented in 1973 and the first 32-bit processors were available in 1979.

While you've got the time machine, can you fix it so that "network byte order" and Intel endianness are the same too?

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swiley 3256 days ago
Or rather keep Intel from munging the order their processors write bytes in.
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adrianratnapala 3255 days ago
What?
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drewg123 3256 days ago
The 32-bit Vax 11/780 was introduced in 1977 and IEEE 802.3 was not finalized until 1983. So they could/should have done something about it I think.

Come to think of it, the Vax was little endian (like Intel).

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jandrese 3256 days ago
It's all they needed. 6 bytes per address, and 2 more bytes to mark the protocol. Back in the 70s and 80s memory was very expensive and developers bent over backwards to save bytes everywhere. This is also why IP addresses are only 32 bits long, even though they knew that it wouldn't be enough if the protocol went global.

Hindsight is 20/20, and a lot of times people don't appreciate the constraints these old systems had. This was being developed decade before the Commodore 64 came out with its luxurious 64 kilobytes of memory (39k usable).

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jimktrains2 3256 days ago
They didn't feel like they needed those 2 bytes and, hey, why waste space?

Also, was a "byte" standardized at the time? Didn't they still have systems working in not-8-bit "byte", nibbles, byte, and 2-byte boundaries?

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danesparza 3256 days ago
From https://en.wikipedia.org/wiki/Byte#History - a byte was in the process of getting standardized at around the same time.
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