Re: When it Rains, it Pours ....
- From: William Warren <william_warren_nonoise@xxxxxxxxxxx>
- Date: Mon, 19 Sep 2005 14:31:32 -0400
TELECOM Digest Editor noted when questioning William Warren:
>> [TELECOM Digest Editor's Note: On the older Think Pads (models 770
>> or 770x at least) F1 at time of booting brings up a BIOS menu and a
>> choice of options i.e. boot from CD, from hard drive, from floppy
>> (and other choices I do not understand, such as from 'network', from
>> 'PCMCIA card' and other places. Exactly how one boots from 'network'
>> or from 'PCMCIA card' when those devices do not come to life until
>> Windows turns them on confuses me. [snip] PAT]
> Pat,
> It's asking if you want to start a bootp request from your Ethernet
> card, which would broadcast for a "boot" server to provide the
> operating system for you over the network.
> In other words, it's giving you the option that's used for "Diskless
> Workstations", which don't have a hard disk, to download your OS from
> another network node and start it in memory. It's the same process
> your BIOS performs during boot, except that the image that's loaded
> into your machine's ram comes from another computer on your LAN, not
> from your hard drive.
[snip]
> [TELECOM Digest Editor's Note: But I still do not understand _how_
> the network card, or PCMCIA or whatever is able to do that job without
> first itself getting installed by (for example) Windows or whatever OS
> is in the terminal/workstation. I mean, that would be great if I could
> just turn on the laptop and have its OS installed by the desktop Win
> 2000. But how? PAT]
Pat, the network card is able to do that job because it contains a
small computer program stored on ROM, which tells it what to do. This
is the same process your computer goes through when it boots: a small
computer program, stored in your computer's ROM, tells the machine to
read the first (boot) sector from the first hard disk drive into RAM,
and to transfer control to it. From there, the boot code that was read
from the hard disk takes over and reads the operating system into RAM,
thus booting the OS.
With BOOTP, the ROM is on the Ethernet card: it's usually an extra
chip that you have to buy separately and plug in yourself. The
instructions in the rom tell the microcontroller on the Ethernet card
to issue a BOOTP broadcast, thus requesting a response from a BOOTP
server, and the server responds with the "bootstrap" code that the
computer uses to find an OS image and load it into memory.
It's the same result, just from a different source.
GIYF:
http://www.microsoft.com/mspress/books/sampchap/6163a.asp (General Information)
http://www.cis.njit.edu/~cis456/protected/lesson23/single23.html
(Details of the protocol)
William
(Filter noise from my address for direct replies)
.
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