Page 365 - DCAP103_Principle of operating system

Principles of Operating Systems

Notes 2. Each process contains at least ...................... .
( a) one thread (b) two threads
( c) four threads (d) none of these.
3. A thread normally runs in ...................... .
( a) User mode (b) Safe mode.
( c) both (a) and (b) (d) None of these
4. A semaphore is created using the ...................... API function.
( a) APISemaphore (b) CreateSemaphore
( c) WaitSemaphore (d) None of these
12.2 Booting Windows 2000

Before Windows 2000 can start up, it must be booted. The boot process creates the initial processes
that bring up the system. In this section, we will briefly discuss how the boot process works for
Windows 2000. This short assembly language program reads the partition table to see which
partition contains the bootable operating system. When it finds the operating system partition,
it reads in the first sector of that partition, called the boot sector, and jumps to it. The program
in the boot sector reads its partition’s root directory, searching for a file called ntldr (another
piece of archaeological evidence that Windows 2000 is really NT). If it finds that file, it reads
the file into memory and executes it. Ntldr loads Windows 2000. As an aside, there are several
versions of the boot sector, depending on whether the partition is formatted as FAT-16, FAT-32,
or NTFS. When Windows 2000 is installed, the correct version of the master boot record and
boot sector are written to disk.
Ntldr now reads a file called Boot.ini, which is the only configuration information not in the
registry. It lists all the versions of hal.dll and ntoskrnl.exe available for booting in this partition.
The file also provides many parameters, such as how many CPUs and how much RAM to use,
whether to give user processes 2 GB or 3 GB, and what rate to set the real-time clock to. Ntldr
then selects and loads hal.dll and ntoskrnl.exe files as well as bootvid.dll, the default video
driver for writing on the display during the boot process. Ntldr next reads the registry to find
out which drivers are needed to complete the boot (e.g., the keyboard and mouse drivers, but
also dozens more for controlling various chips on the parentboard). Finally, it reads in all these
drivers and passes control to ntoskrnl.exe.
Once started, the operating system does some general initialization and then calls the executive
components to do their own initialization. For example, the object manager prepares its name
space to allow other components call it to insert their objects into the name space. Many
components also do specific things related to their function, such as the memory manager setting
up the initial page tables and the plug-and-play manager finding out which I/O devices are
present and loading their drivers. All in all, dozens of steps are involved, during which time
the progress bar displayed on the screen is growing in length as steps are completed. The last
step is creating the first true user process, the session manager, smss.exe. Once this process is
started and running, booting is completed.
The session manager is a native Windows 2000 process. It makes true system calls and does not
use the Win32 environment subsystem, which is not even running yet. In fact, one of its first
duties is to start it (csrss.exe). It also reads the registry hives from disk and learns what else it is
supposed to do. Typically its work includes entering many objects in the object manager’s name
space, creating any extra paging files needed, and opening important DLLs to have them around
all the time. After it has done most of this work, it creates the login daemon, winlogon.exe.
At this point, the operating system is up and running. Now it is time to get the service processes
(user space daemons) going on and allow users to log in. Winlogon.exe first creates the
authentication manager (lsass.exe), and then the parent process of all the services (services.exe).
The latter looks in the registry to find out which user space daemon processes are needed and
what files they are in. It then starts creating them. The fact that the disk is generally being heavily

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