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From: ibmarc!drake@UUNET.UU.NET (Sam Drake)
Newsgroups: comp.lang.asm370
Subject: Re: CTCAs
Message-ID: <8912090157.AA05141@brazos.rice.edu>
Date: 8 Dec 89 19:51:16 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: IBM 370 Assembly Programming Discussion List <ASM370%UCF1VM.BITNET@ricevm1.rice.edu>
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Organization: The Internet
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In article <89334.194519CMH117@PSUVM.BITNET> CMH117@PSUVM.BITNET (Charles
        Hannum) writes:
>  Exactly what *are* Channel-To-Channel Adapters (CTCAs), and what do
>  they (and CP COUPLE) do?

CTCAs are devices that allow two S/370 mainframes to communicate at
channel speeds.  So while most 370 I/O involves the CPU talking to
a disk drive or some peripheral, CTCA I/O is CPU-to-CPU.

One side can read a CTCA and will get an interrupt when the other
side writes it...and vice versa.  The IBM 3088 is a stand-alone
product that provides channel to channel adapters; up to 8 mainframes
can be hooked to the 3088 and they can all communicate using CTC protocols
at full channel speed (4.5MByte/sec, I think).

Under VM, virtual machines can manipulate real CTCs (if they are
ATTACHed or DEDICATEd to the virtual machine), and can also use
virtual CTCs.  Virtual CTCs don't hook to any real hardware anywhere,
but rather can be used to communicate between two virtual machines.
Each virtual machine DEFINEs a CTC; the COUPLE command is used by
one virtual machine or the other to connect them together.

Sam Drake / IBM Almaden Research Center