Page 340 - DCAP103_Principle of operating system

Unit 11: Operating System Structure

used. It builds upon the kernel process and thread objects and adds extra functionality to them. Notes
It is the key to multiprogramming in Windows 2000.
The memory manager implements Windows 2000’s demand-paged virtual memory architecture.
It manages the mapping of virtual pages onto physical page frames. It thereby enforces the
protection rules that restrict each process to only access those pages belonging to its address
space and not to other processes’ address spaces (except under special circumstances).
The security manager enforces Windows 2000’s elaborate security mechanism, which meets the U.S.
Department of Defense’s Orange site C2 requirements. The Orange site specifies a large number of
rules that a conforming system must meet, starting with authenticated login through how access
control is handled, to the fact that virtual pages must be zeroed out before being reused.
The cache manager keeps the most recently used disk blocks in memory to speed up access to
them in the (likely) event that they are needed again. Its job is to figure out which blocks are
probably going to be needed again and which ones are not. It is possible to configure Windows
2000 with multiple file systems, in which case the cache manager works for all of them, so each
one does not have to do its own cache management. When a block is needed, the cache manager
is asked to supply it. If it does not have the block, the cache manager calls upon the appropriate
file system to get it. Since files can be mapped into processes’ address spaces, the cache manager
must interact with the virtual memory manager to provide the necessary consistency. The amount
of space devoted to caching is dynamic and can increase or decrease as demands on it change.

The plug-and-play manager is sent all notifications of newly attached devices. For some devices,
a check is made at boot time and not thereafter. Other devices, for example, USB devices, can
be attached at any time and their attachment triggers a message to the plug-and-play manager,
which then locates and loads the appropriate driver.
The power manager rides herd on power usage. This consists of turning off the monitor and
disks after they have been idle for a while. On laptops, the power manager monitors battery
usage and takes action when the battery is about to run dry. Such action typically tells programs
to save their files and prepare for a graceful shutdown.
The configuration manager is incharge of the registry. It adds new entries and looks up keys
when asked to.
The local procedure call manager provides for a highly-efficient interprocess communication
used between processes and their subsystems. Since this path is needed to carry out some
system calls, efficiency is critical here, which is why the standard interprocess communication
mechanisms are not used.

The Win32 GDI executive module handles certain system calls (but not all of them). It was
originally in user space but was moved to kernel space in NT 4.0 to improve performance. The
GDI (Graphics Device Interface) handles image management for the monitor and printers. It
provides system calls to allow user programs to write on the monitor and printers in a device-
independent way. It also contains the window manager and display driver. Prior to NT 4.0, it,
too, was in user space but the performance was disappointing, so Microsoft moved it into the
kernel to speed it up. It is worth mentioning that Figure 11.1 is not at all to scale. For example, the
Win32 and graphics device interface module are larger than the rest of the executive combined.
At the top of the executive is a thin layer called system services. Its function is to provide an
interface to the executive. It accepts the true Windows 2000 system calls and calls other parts
of the executive to get them executed.

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