An Interrupt Request Level (IRQL) is a hardware-independent means with which

Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

prioritizes

interrupt In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted ...

s that come from the system's processors. On processor architectures on which Windows runs, hardware generates signals that are sent to an interrupt controller. The interrupt controller sends an

interrupt request In a computer, an interrupt request (or IRQ) is a hardware signal sent to the processor that temporarily stops a running program and allows a special program, an interrupt handler, to run instead. Hardware interrupts are used to handle events s ...

(or IRQ) to the CPU with a certain priority level, and the CPU sets a mask that causes any other interrupts with a lower priority to be put into a pending state, until the CPU releases control back to the interrupt controller. If a signal comes in at a higher priority, then the current interrupt will be put into a pending state; the CPU sets the interrupt mask to the priority and places any interrupts with a lower priority into a pending state until the CPU finishes handling the new, higher priority interrupt. Windows maps not only hardware interrupt levels to its internal interrupt table but also maps software interrupts. The mappings in this table are called Interrupt Request Levels, or IRQLs, and a separate IRQL is kept for each processor in a multiprocessor system. The IRQL values are specific to the

x86 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel, based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088. Th ...

, IA64 and

AMD64 x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit extension of the x86 instruction set. It was announced in 1999 and first available in the AMD Opteron family in 2003. It introduces two new operating modes: 64-bit mode an ...

processor architectures that Windows can run on, though theoretically they can support other CPUs that use a similar interrupt scheme (such as the

DEC Alpha Alpha (original name Alpha AXP) is a 64-bit reduced instruction set computer (RISC) instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC). Alpha was designed to replace 32-bit VAX complex instruction set computers ( ...

and MIPS, which were supported briefly on early versions of Windows). This means that APCs (asynchronous procedure calls), user threads and kernel mode operations can be interrupted, and the system must run them at an IRQL lower than the thread scheduler (or "dispatcher").{{citation, url=http://download.microsoft.com/download/e/b/a/eba1050f-a31d-436b-9281-92cdfeae4b45/irql_thread.doc, title=Scheduling, Thread Context, and IRQL, date=April 26, 2016, publisher=

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

, pages=6–7, access-date=April 26, 2016, archive-url=https://web.archive.org/web/20161022141500/http://download.microsoft.com/download/e/b/a/eba1050f-a31d-436b-9281-92cdfeae4b45/irql_thread.doc, archive-date=October 22, 2016, url-status=dead

References

Windows administration

See also

References