[TUHS] updated: loop networks at Bell Labs
Heinz Lycklama
heinz at osta.com
Fri Jun 19 11:01:16 AEST 2020
A later memo in 1978 provides a Figure that shows how the I/O Loop
was used to support multiple satellite processors. See here:
https://www.tuhs.org/Archive/Documentation/TechReports/Heinz_Tech_Memos/TM-78-3114-2_A_Minicomputer_Satellite_Processor_System_19780322.pdf
Heinz
On 6/16/2020 3:41 PM, Paul Ruizendaal wrote:
> With some further reading and research (and the kind help of Heinz
> Lycklama and Jon Steinart) I’ve found that my understanding of early
> loop networks at Bell Labs confused several different systems. As far
> as I can currently tell there were at least 4 different loop networks
> developed around 1970 at Murray Hill.
>
> 1. The first one is the “Newhall Loop” (paper published in 1969). This
> loop used twisted pair cabling, ran at about 3Mhz and used variable
> sized messages. It seems to have used some sort of token to coordinate
> between hosts. This might have been the network that Ken Thompson
> recalled as having been in operation when he arrived at the labs in 1966.
>
> 2. The second one appears to have been the “Pierce Loop”, as described
> in 3 BSTJ papers submitted in 1970/71. This one was coax based, used
> T1 compatible frames and was used to connect H516 computers with
> various bits of equipment. It seems to have had a very short life
> span. Part of my confusion was that the term Pierce Loop also appears
> to have been used in a generic sense to denote loop networks with
> fixed-sized frames.
>
> 3. The third one is the “Weller Loop” (paper published in 1971). This
> loop used coax cabling, ran at 3.3Mhz and used fixed 35 bit
> frames/cells. Each cell carried one address byte and two data bytes.
> One participant on the loop was the controller and effectively polled
> the other stations. In its 1971 form it appears to have been for the
> H516’s only and was referred to as a “Serial I/O bus”. This is what
> Jon Steinhart was talking about.
>
> The Weller loop was later redesigned (memo written in 1973) to
> interface with PDP-11’s as well. Heinz Lycklama used this loop in 1974
> to connect several systems running (rump) Unix - see his paper about
> peripheral Unix here:
> https://www.tuhs.org/Archive/Documentation/TechReports/Heinz_Tech_Memos/TM-75-1352-2_Emulation_of_UNIX_on_Peripheral_Processors_19750109.pdf
>
> This Serial I/O bus remained in use for several years at least.
>
> 4. The fourth and best known one is the “Spider Loop” (memo published
> in 1974, but operational from 1972). Twisted pair cabling, using T1
> compatible frames. In use until about 1978. Main uses appear to have
> been the ‘nfs’ file store and the ‘npr’ remote printing service.
>
> My conclusion from all that is that in 1974 Unix had access to two
> networks, Spider and the Serial I/O bus. For both, first experiments
> would have been in 1973. It is hard to be sure which one came first.
> If I had to venture a guess today, I’d say that Spider connected to
> Unix several months before the Weller loop (even though the 1st
> generation Weller loop preceded Spider). Maybe the conclusion is that
> both happened more or less in parallel: Weller was also one of the
> designers of the Spider hardware.
>
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