Re: Apologies and Arcnet


Henri J. Socha (amdahl!drivax!socha@ames.arpa)
24 Nov 87 18:34:09 GMT


Answering your questions even as I read them:

In article <8711222235.AA13789@ARES.MIT.EDU> martillo@ATHENA.MIT.EDU writes:
>I noticed arcnet being discussed here. Now my friends at Clearpoint
>use arcnet networking cards with vme bus interfaces for some sort of
>distributed memory testing. After seeing arcnet mentioned in this
>newsgroup, I have become curious.
>
>Where does arcnet come from?
 It was developed at Datapoint Corp. of San Antinio Texas in 1976 by
 members of the Advanced Product Development (R&D) group I was a memeber.
 Datapoint (and people in this group) also architected the "Intel 8008",
 the first dBase type of programme (that I know of), the 2nd PC (IBM's 5100
 was first), one of the first glass TTYs, etc. (But enough of this.)

 The ARCnet hardware and protocol was designed by one Engineer
 with the help of two techs. and about 3 other people who discussed it
 and gave advice/suggestions. The limitations of board (TTL MSI) space
 generated some of its idiocyncracies for example the DID is transmitted
 twice on the wire.

 The changes to Datapoint's DOS similar to what happens/happened when you
 go from PC-DOS 2.x to 3.x was done by one individual. This DOS used a similar
 similar system to the NET USE of PC-DOS call MOUNT.
 By the way, remember that we are talking about a networking OS in 1976!

>Who uses it and why (instead of some other networking scheme)?

 It was first used inhouse to connect multiple Datapoint machines together so
 that production/purchasing/etc. could access common databases and allow more
 that 10 DataShare users access to one database.

 The only other network known (by us in R&D) was
 Ethernet (the original 3MegaBaud XEROX one). It was decided (demanded)
 that a system be used where assured transmission within a maximum time
 be used. The concept of CSMA/CD (Ethernet, etc.) still is revolting to me.

 ARC has very simple installation using what I call a connected star
 configuration. And is VERY robust in that most anything that happens to
 the cable (connections/disconnections/wiring changes) can be done on a live
 system with reconfiguration handled automatically by the hardware.
 I.E. as long as your node doesn't need something now disconnected, your node
 does not even know that the break occured.

 The robustness, its reasonable speed, etc. have put it in I hear over 400,000
 installations (said so in some magazine in an article about OTHER networks!)
 I know of users in the
 * Business industry (Datapoint customers like the local city government with
   all departments on an ARCnet of many nodes.)
 * factory floor (large German manufacturer)
 * Actually anywhere you see nets, you'll see ARCnet.

 Remember, It was one of the first high speed commercial PC machine nets.
 And is still up there performance-wise against all newcommers in this market.
 (OK, not 50MegaBaud Hyperchannel but we're talking PCs here!)

>What are the achievable data rates?

 Ask anyone about effective rates and you get down to issues of OS
 performance as well (how well/much can the OS handle). But let me mention
 some interesting facts even if not quite what you requested.
 * The system is defined as 2.5MBaud but because it uses an isocronous(sp?)
   transmission scheme (resync on each character in a message) to send
   8 data bits you must send 11 baud (3 sync bits preceed each data bit)
   therefore the effective data rate is about 1.8MegaBit per second.
 * When one person was testing some (bad?) hardware on a live network
   while many REAL users were using it, the response time degraded.
   The network of course still operated correctly but was loaded down
   by over 400 (256 byte) messages per second.
 * A live ARC system (at Datapoint again) had over 200 nodes on it (max is 255).
   About 150+ were active on the net and the message rate was about 200
   per second. (And yes, I saw this myself.) Response time was good enough
   that all engineering nodes in R&D were diskless (not even diskettes).
   And, many/most other nodes were diskless too. Dedicated files servers
   were used but the OS, a newer one written in '80 called RMS, considered
   any node a requestor or server so you could go to the Server and use it
   like any other machine. They were just used as Servers so that all of
   memory could be a disk cache (fully dynamic, run an App. and cache shrinks).

   Response time? OK, not as good as a local disk but good enough that it was
   not an issue. In fact, in one test a copy from file server to file server
   by a user machine was slightly faster than a local copy! Why? the caching!
   The file server could pre-read and post-write whole tracks to/from the disk
   optimally servicing requests from the network. Meanwhile the programme in
   the local machine was being handed BIG buffers of data that it just "wrote"
   back out over the net back to a file server.

>Where can I get literature on arcnet?

 Try: Standard Micro Systems (they make the chip and sell a PC board)
        Datapoint (of course) (They may have an 800 number)
        Radio Shack (UGH!) Does sell some ARC hardware.
        Novell puts its LAN on ARCnet (and one of the fastest implementations)

>Yakim Martillo
                        Shalom v'litraot Yakim

--
UUCP:...!amdahl!drivax!socha					  WAT Iron'75
"Everything should be made as simple as	possible but not simpler."  A. Einstein



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