Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!YKTVMH.BITNET!PERSHNG
From: PERSHNG@YKTVMH.BITNET ("John A. Pershing Jr.")
Newsgroups: comp.lang.asm370
Subject: (none)
Message-ID: <8912011718.AA28894@brazos.rice.edu>
Date: 1 Dec 89 17:02:19 GMT
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Reply-To: IBM 370 Assembly Programming Discussion List <ASM370%UCF1VM.BITNET@ricevm1.rice.edu>
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Channel-to-Channel Adaptors are a *hardware* facility for connecting a
pair of '370s together by "simply" wiring a channel port of one machine
to the channel port of the other machine.  A CTC-A is sort-of like a
"null modem", although its a bit more convoluted than simply crossing a
couple of wires.

The current incarnation of this hardware device is the 3088 box, which
will interconnect up to 8 processors into sort-of a "star" network.

A *virtual* CTC-A is an emulation of a *real* CTC-A, done by CP on behalf
of a pair of virtual machines.  E.g., machine FRED says "DEFINE 300 AS
CTCA" and machine JOE says "DEFINE 400 AS CTCA" and then FRED says
"COUPLE 300 TO JOE 400" (or, alternately, JOE can issue the COUPLE
command).  From the point of view of the two virtual machines, it is as
if an SE came into the machine room and wired up the CTC-A connection,
only it happens a lot faster.  After they are COUPLEd, the two machines
can use this (virtual) CTC-A exactly as they would use a *real* CTC-A.

For additional details, see SA22-7091, "IBM Channel-to-Channel Adapter".

      John Pershing
      IBM Research, Yorktown Heights