Comments by "Lawrence D’Oliveiro" (@lawrencedoliveiro9104) on "ALOHAnet: Grandfather of All Computer Networks - Computerphile" video.

  1. 9:54 Back when Ethernet was expensive, Apple developed its own, cheaper† “LocalTalk” layer-2 connection system for its AppleTalk protocol stack. Besides the much lower bandwidth and lower-spec wiring, another way they kept the cost down was to omit the collision-detection hardware. An Ethernet node could notice if someone else started transmitting while it was doing so, but LocalTalk could not. Instead of being “CSMA/CD” (the “CD” standing for “Collection Detection”), LocalTalk was “CSMA/CA” (the “CA” standing for “Collision Avoidance”). †Yes, “Apple” and “cheaper” in the same sentence. Not something that happened very often, even back then.
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  2. 2:10 The later term for this separate processor on the ARPAnet was “Interface Message Processor” or “IMP”. It was probably necessary because IBM mainframes did not like to be interrupted for every little bit or byte of data -- their I/O was done through elaborate “channel” processors which could be given sequences of operations to perform without bothering the CPU until the sequence was complete -- or some unusual situation arose (e.g. an I/O error). This probably also eased the problem of implementing the network, because the IBM OS wouldn’t have been interactive. IBM preferred terminals that operated in “block mode”, where you had fields defined on-screen by previous computer output, that you filled in locally, and nothing got sent back to the mainframe until you hit the “Send” key.
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  3. It was probably efficient taking the cost of the hardware into account. As in, with the technology available at the time, there was no way to increase the utilization efficiency by much without spending disproportionate amounts of money.
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  4. You can solve that the same way it’s done in TCP -- by putting sequence numbers on the packets.
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  5. But Ethernet was.
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  6. They really get up your nose.
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  7. Typical expensive and proprietary IBM technology. Also had its own reliability problems. They looked down on Ethernet, but Ethernet eventually wiped them out.
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