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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 65
34
INTRODUCTION
CHAP. 1
I/O addresses 0x60 to 0x64, the floppy disk controller was interrupt 6 and used I/O
addresses 0x3F0 to 0x3F7, and the printer was interrupt 7 and used I/O addresses
0x378 to 0x37A, and so on.
So far, so good. The trouble came in when the user bought a sound card and a
modem card and both happened to use, say, interrupt 4.
They would conflict and
would not work together. The solution was to include DIP switches or jumpers on
every I/O card and instruct the user to please set them to select an interrupt level
and I/O device addresses that did not conflict with any others in the user’s system.
Teenagers who devoted their lives to the intricacies of the PC hardware could
sometimes do this without making errors. Unfortunately, nobody else could, lead-
ing to chaos.
What plug and play does is have the system automatically collect information
about the I/O devices, centrally assign interrupt levels and I/O addresses, and then
tell each card what its numbers are. This work is closely related to booting the
computer, so let us look at that.
It is not completely trivial.
1.3.6 Booting the Computer
Very briefly, the boot process is as follows. Every PC contains a parentboard
(formerly called a motherboard before political correctness hit the computer indus-
try). On the parentboard is a program called the system
BIOS
(
Basic Input Out-
put System
). The BIOS contains low-level I/O software, including procedures to
read the keyboard, write to the screen, and do disk I/O, among other things. Now-
adays, it is held in a flash RAM, which is nonvolatile but which can be updated by
the operating system when bugs are found in the BIOS.
When the computer is booted, the BIOS is started.
It first checks to see how
much RAM is installed and whether the keyboard and other basic devices are in-
stalled and responding correctly.
It starts out by scanning the PCIe and PCI buses
to detect all the devices attached to them.
If the devices present are different from
when the system was last booted, the new devices are configured.
The BIOS then determines the boot device by trying a list of devices stored in
the CMOS memory. The user can change this list by entering a BIOS configuration
program just after booting. Typically, an attempt is made to boot from a CD-ROM
(or sometimes USB) drive, if one is present.
If that fails, the system boots from the
hard disk. The first sector from the boot device is read into memory and executed.
This sector contains a program that normally examines the partition table at the
end of the boot sector to determine which partition is active. Then a secondary boot
loader is read in from that partition.
This loader reads in the operating system
from the active partition and starts it.
The operating system then queries the BIOS to get the configuration infor-
mation. For each device, it checks to see if it has the device driver. If not, it asks
the user to insert a CD-ROM containing the driver (supplied by the device’s manu-
facturer) or to download it from the Internet.
Once it has all the device drivers, the
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