At 10:51 AM -0500 12/13/05, [EMAIL PROTECTED] wrote:
At 12:43 AM -0800 12/13/2005, Clark Martin wrote:
DMA (Direct Memory Access). A separate controller chip that
handles data transfers to/from memory. It is also used by other
functions such as SCSI. Now here I'm not sure what happens but
even though DMA should be taking a lot of the load off the CPU
LocalTalk transfers still slow things down. I suspect that the
software is still taking control of the CPU during the packet
transfer but using DMA to for the transfer.
Correct. The DMA packet is only 8 to 64 bytes. So there are
multiple interrupts per packet ... and since the classic OS was only
preemptive at fork level, this ment a LOT of context switching for
sub-packet building. bog bog bog lag lag lag.
The capabilities of this chip determined the AppleTalk Protocol
even AT over Ethernet (EtherTalk). The limitations of AT caused by
this are one of the reasons that Apple is abandoning it, in
particular the limitation on packet size of 625 bytes.
ASICs are cheap. So it was political, not hardware that caused the change.
They are now but when the Mac first came out they weren't very
common. And while a newer more efficient network design could be
done now, they are still stuck with the AppleTalk protocol determined
by the early hardware.
Apple gutted their networking group a decade ago. Remember - Open
Transport was actually licensed Mentat/TCP wedged into the OS. The
rest of the world was going to IP. And the lack of interoperability
at the higher protocol levels was keeping Apple out of much of the
business world. Like DECnet and SNA, AppleTalk needed to die.
sigh. As much as I hate that Tiger has dumped AFP/AT, it had to
happen. And I'll bet printing support over AT isn't far behind...
Sometimes folx like us need to be dragged kicking and screaming into
the future. :\
Speak for yourself. I have no problem with AT going away. I liked
AT and it had it's advantages in it's day. But it had little room to
grow.
It does kind of concern me that IP seems stagnant. While there is
IPv6 and 10K packets they don't seem to moving ahead.
--
Clark Martin
Redwood City, CA, USA
Macintosh / Internet Consulting
"I'm a designated driver on the Information Super Highway"
--
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