Q. What kind of interrupt latency does Windows NT
provide?
A. Interrupt latency is a function of the drivers that are
running and what they do at interrupt time. The Windows NT design
philosophy encourages drivers to do as little work as possible. The
kernel architecture generally let's a driver do a very small amount of
work at interrupt time and use a DPC (deferred procedure call) to do
driver related processing at a lower IRQL. This design allows for very
short interrupt service routines and results in reduced interrupt
latency.
Q. Can the kernel respond to an interrupt while actually
executing kernel code?
A. Yes, although there are some spots where the IRQL level is
raised or where interrupts are disabled. In general, the kernel is not
preemptible, but interrupts can and do happen during
execution of the kernel. The rules for interrupts are very similar to
other systems. Windows NT has a multilevel interrupt mask. Higher
priority interrupts can occur when the mask allows them to occur.
Changing the mask raises the level where lower level
interrupts can not occur.
Q. Does Windows NT have a fixed priority scheduler?
A. Windows NT supports 32 priority levels which can be
assigned to particular threads. Sixteen of these priority levels are
variable; that is, the scheduler adjusts your priority up
and down as events occur. Sixteen levels are fixed priority or "real-
time" where the operating system cannot adjust the priority level.
The Win32 API allows access to both the variable and fixed priority
classes and to most of the 16 priorities in each level.
Q. Does Windows NT support asynchronous I/O?
A. Yes. Windows NT provides three different completion
notification mechanisms allowing for a very flexible approach to
using asynchronous I/O.
Q. Does Windows NT wait for a clock tick before it responds to
an interrupt?
A. Assuming that interrupts are not disabled or masked at
that level, the system handles the interrupt immediately.
Q. Does Windows NT support a real-time or contiguous file
system?
A. With file systems, the bulk of the performance cost occurs
when a file needs to grow. With the NTFS file system, Windows NT
can preallocate space to files although it is not strictly contiguous.
The RAW file system provides unstructured storage on an
unformatted disk volume so that the application itself can control the
contents of the file system.
Q. Does Windows NT support memory locking?
A. Windows NT allows an application to control the size of its
working set. An application can lock memory into its working set.
Q. Does Windows NT support direct I/O and memory
access?
A. In general, Windows NT does not allow an application
access to I/O ports directly. If this is needed, a driver needs to be
written.
Previous Page Home Next Page