Editing ALOHAnet (section)

== Hardware ==

The central node communications processor was an [[HP 2100]] minicomputer called the Menehune, which is the [[Hawaiian language]] word for dwarf people,<ref>{{Hawaiian Dictionaries |Menehune |accessdate= August 11, 2011}}</ref> and was named for its similar role to the original [[ARPANET]] [[Interface Message Processor]] (IMP) which was being deployed at about the same time. In the original system, the Menehune forwarded correctly received user data to the UH central computer, an [[IBM System 360]]/65 time-sharing system. Outgoing messages from the 360 were converted into packets by the Menehune, which were queued and broadcast to the remote users at a data rate of {{nowrap|9600 bit/s}}. Unlike the half-duplex radios at the user TCUs, the Menehune was interfaced to the radio channels with full-duplex radio equipment.<ref>{{Cite journal |last=Kuo |first=Franklin F. |author-link=Franklin F. Kuo |date=November–December 1981 |title=Computer Networks - the ALOHA System |url=https://nvlpubs.nist.gov/nistpubs/jres/086/jresv86n6p591_A1b.pdf |journal=[[Journal of Research of the National Bureau of Standards]] |language=en |volume=86 |issue=6 |pages=591–595 |doi=10.6028/jres.086.027 | pmid=34566062  |pmc=6753009 |issn=0160-1741 |access-date=2014-07-12|doi-access=free }}</ref>

The original user interface developed for the system was an all-hardware unit called an ALOHAnet Terminal Control Unit (TCU) and was the sole piece of equipment necessary to connect a terminal into the ALOHA channel. The TCU was composed of a UHF antenna, transceiver, modem, buffer and control unit. The buffer was designed for a full line length of 80 characters, which allowed handling of both the 40- and 80-character fixed-length packets defined for the system. The typical user terminal in the original system consisted of a [[Teletype Model 33]] or a dumb CRT user terminal connected to the TCU using a standard [[RS-232]] interface. Shortly after the original ALOHA network went into operation, the TCU was redesigned with one of the first Intel microprocessors, and the resulting upgrade was called a Programmable Control Unit (PCU).

Additional basic functions performed by the TCUs and PCUs were generation of a cyclic-parity-check code vector and decoding of received packets for packet error detection purposes, and generation of packet retransmissions using a simple random interval generator. If an acknowledgment was not received from the Menehune after the prescribed number of automatic retransmissions, a flashing light was used as an indicator to the human user. Also, since the TCUs and PCUs did not send acknowledgments to the Menehune, a steady warning light was displayed to the human user when an error was detected in a received packet. Considerable simplification was incorporated into the initial design of the TCU as well as the PCU for interfacing a human user into the network.

In later versions of the system, simple radio relays were placed in operation to connect the main network on the island of Oahu to other islands in Hawaii, and Menehune routing capabilities were expanded to allow user nodes to exchange packets with other user nodes, the [[ARPANET]], and an experimental satellite network.<ref name=binder1 />