At 10:25 PM -0700 6/27/00, John Tree wrote:
>If the 4GB hardware based limit is on SCUSI and not ATI devices (such as the
>internal drive) then what is the max size of an external drive I can connect
>via SCUSI directly to the 2400?
The limit is only relevant for SCSI Disk Mode. External SCSI drives
can be any size you like.
To understand this better, you need to know that the 4GB problem with
SCSI Disk Mode is not a hardware limit, but rather a software bug.
The way SCSI Disk Mode works is that instead of booting MacOS, the
PowerBook starts running a special program stored in the PowerBook's
ROM. This program reconfigures the PowerBook's SCSI interface to
listen for SCSI commands instead of generating them. Any time there
is a SCSI command addressed to the PowerBook's SCSI ID, the SCSI Disk
Mode software translates it to a command for the PowerBook's own hard
drive, processes that command locally, and then sends the results
back over SCSI.
The 4GB problem is a bug in the SCSI Disk Mode program, not a problem
with the SCSI or IDE hardware in the computer. Unfortunately it
can't be fixed with a System software update, because the SCSI Disk
Mode program is stored in the PowerBook's ROM, which cannot be
updated or replaced. (Starting with the bronze keyboard PowerBook
G3, PowerBooks have flash ROM, meaning their ROM can be updated just
by running a program supplied by Apple. But earlier models like the
2400 have mask ROM, which can never be changed after production.)
The bug actually affects many PowerBook models. Apple didn't find
out about it until they started testing PowerBooks which were going
to ship with hard drives larger than 4GB. I believe this happened
during development of the original PowerBook G3 (the one which is
sometimes called a "3500" because it looks just like a PB 3400).
Naturally they fixed the bug for that model, but every previous
PowerBook model has the 4GB SCSI disk mode bug.
Tim Seufert
----------
Duo/2400 List, The friendliest place on the Net!
A listserv for users and fans of Mac subportables.
FAQ at <http://www.themacintoshguy.com/lists/DuoListFAQ.shtml>
Be sure to visit Mac2400! <http://www.sineware.com/mac2400>
XRouter | Share your DSL or cable modem between multiple computers!
Dr. Bott | Now $199.99 <http://www.drbott.com/prod/MIH120.html>
PowerBook Guy is | Click here!
Everything PowerBook! | http://www.powerbookguy.com
Midwest Mac Parts ][ <http://www.midwestmac.com>
After-market parts for Macs. ][ 888-356-1104 ][
MacResQ Specials: LaCie SCSI CDR From $99! PowerBook 3400/200 Only $879!
Norton AntiVirus 6 Only $19! We Stock PARTS! <http://www.macresq.com>
