Date: Wed, 5 Sep 2007 15:55:04 -0500
From: Mark Tapley <mtapley at swri.edu>
Subject: Re: D-shell sizes
To: cctalk at
classiccmp.org
Message-ID: <p06240819c304c5a417d4(a)[129.162.152.69]>
Content-Type: text/plain; charset="us-ascii" ; format="flowed"
<Hangs head in shame>
I am *so* sorry - I left off the correct letter (thought it was "B",
just wasn't sure) in hopes of *avoiding* kicking off the annual
D-shell connector nomenclature thread.
Have we dug up the horse bones, beat them into flour, baked the flour
into bread, and punched it down enough now?
Guess not. I'll add to the mess:
<chuckle> Going back to your earlier topic, so I really should nest
another "Was:" up there. :-)
Jim's old Mac had the same kind of SCSI connector. You probably
never looked closely at it at an early Geekathon. Or maybe he only
brought it to the first one and brought the Outbound the next few
years.
Anyway, the upgrades for the 128K and 512K[E] models which provided a
SCSI port, typically routed the ribbon cable around the edge of the
battery compartment. A few ran the cable over the floppy connector.
The more elegant ones actually provided a replacement battery
compartment cover which had the DB25 connector (awww, back to the
topic) mounted in the plastic cover. One removed the old battery
compartment cover, routed the SCSI ribbon cable out of the case
around the edge of the battery compartment and secured the new cover
over the battery compartment, which gave one a DB25 connector mounted
over the battery compartment.
There were several SCSI upgrades for those old machines. The
SCSI-only upgrades usually plugged into the ROM sockets, provided
sockets on top of the upgrade daughter board for the two ROM chips
and then bore a 53C80 and ribbon header. There might have been a
bit more logic, but not much. IIRC, they did require that the host
machine be upgraded to the later 512KE or Plus ROMs because the
original 128K and 512K ROMs did not contain a SCSI port driver.
Other upgrades provided additional memory as well and those typically
required tapping all the CPU lines, so they either used a Killy Clip
(clear plastic receptacle with embedded pins which fits snuggly over
the 68000 DIP) which provided a double row of pins above the clip in
the standard 64 pin DIP spacing, or they relied on headers soldered
directly to the 68000 pins.
My favorite was the NewLife brand upgrades because they provided
eight SIMM sockets on the daughter board. If one had a 512KE, one
could install the NewLife upgrade and add a SCSI port and eight SIMM
sockets. Then two 1MB SIMMs and six 256KB SIMMs later, one had a
4MB (maximum) RAM equipped Mac Plus equivalent, which was supposedly
somewhat faster for reasons I never really understood. The CPU ran
at the same speed, but the Newlife guys claimed some part of their
interface to the peripheral logic or maybe to the RAM was faster.
The advantage of that memory arrangement was that back at that time
(early 90s) 1 MB SIMMs were still close to $100 each, but 256KB SIMMs
cost between free and $5, or $10 if one totally failed one's merchant
skill.
Jeff Walther