Date: Wed, 28 Jul 2004 21:32:40 -0400 From: Fluxstringer <[EMAIL PROTECTED]> Subject: Re: [PCI] External Firewire Bootability
I have been checking in to external firewire drives and would like
to find one that has
fairly large capacity (120 GB +) and is bootable. Problem is
"bootable" doesn't seem to
be a bandied selling point in the specs of many of the most popular brands. My
assumption is, then, that most external firewire Maxtors and others
are not bootable.
How do you know which external firewire drives are bootable?, i.e.,
what is the
technical aspect that makes them bootable? Obviously needs proper ROM read and
driver load at boot. What do you need to look for, exactly?
How do you boot from a Firewire drive when the Mac OS has to be running in order for the firewire extension to be enabled ?
In other words ( Forgive the emphasis here folks . And correct me if and only if I am definitely wrong ) IT CAN'T BE DONE !
To condense and clarify the information in some of the answers already given...
A firewire driver must be loaded at boot time, in order to boot from a Firewire drive.
On older machines, the Firewire driver resides in an Extension in the OS folder, and so you have a chicken and egg problem, which means that you can't boot from a Firewire drive--period. The computer doesn't know how to communicate by Firewire until the extension loads; the extension doesn't load until the OS loads; therefore, you can't boot from a firewire drive, because the OS must be loaded before any firewire devices can communicate with the computer.
On newer machines, and I don't remember exactly which model this starts with, but it wasn't the first that included Firewire, the Firewire Driver is built into the ROM (or flashable firmware, which is what the new machines actually have) of the Macintosh. So when the computer boots, the ROM code is loaded, the firewire driver loads from the ROM contents, and the computer can communicate with Firewire devices before the OS loads. So in the case of newer machines with Firewire boot support in the ROM, they can boot from Firewire devices. This is not a function of the Firewire drive purchased, it is a fucntion of the computer on which it is being used.
In theory, it should be possible to build a Firewire PCI card with a boot ROM on the PCI card which would support Firewire bootability on older Macs, but no-one has done it. This is how SCSI PCI cards work. A driver is present on the PCI card itself stored in a non-volatile (usually flash) memory chip. Part of the Mac boot process is for the computer to read all these PCI card resident drivers at boot up, so that cards with built-in drivers (IDE cards, SCSI cards, video cards) will be able to work before the OS loads.
Jeff Walther
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