A control register is a processor register which changes or controls the behavior of a CPU or other digital device. Common tasks performed by control registers include: In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to commonly used values—typically, the values being in the midst of a calculation at a given point in time. ... CPU can stand for: in computing: Central processing unit in journalism: Commonwealth Press Union in law enforcement: Crime prevention unit in software: Critical patch update, a type of software patch distributed by Oracle Corporation in Macleans College is often known as Ash Lim. ...

• Interrupt control
• Mode switches
• Paging control
• Coprocessor control

In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ... In computer operating systems, paging memory allocation algorithms divide computer memory into small partitions, and allocates memory using a page as the smallest building block. ... This article or section does not cite its references or sources. ...

Control registers in x86 series

• CR0 :

The CR0 Register has 6 bits. The low 5 bits of the CR0 register, and the highest bit. Here is a representation of CR0: x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ...

CR0: |PG|----RESERVED----|ET|TS|EM|MP|PE|

PE - Puts the system into protected mode.

PG - PG turns on memory paging.

MP - The "Monitor Coprocessor" flag, which controls the operation of the "WAIT" instruction.

ET - The Extension Type Flag. ET (also called "R") tells us which type of coprocessor is installed. If ET = 0, an 80287 is installed. if ET = 1, an 80387 is installed.

EM - The Emulate Flag. When this flag is set, coprocessor instructions will generate an exception.

TS - The Task Switched flag. This flag is set automatically when the processor switches to a new task.

• CR1 - Reserved (used in segmentation)

• CR2 - Contains a value called Page Fault Linear Address (PFLA). When a page fault occurs, the address accessed is stored in CR2.

• CR3 - Used when PG is set. CR3 enables the processor to locate the page table directory for the current task. Last 20 bits of CR3 point to Page directory base register (PDBR).

• CR4 - Used in protected mode to control operations such as virtual-8086 support, enabling I/O breakpoints, page size extension and machine check exceptions.

See also

• Protected Mode @wikibooks
• General purpose registers
• Test register
• Debug register
• flag byte
• Status register

General Purpose registers are those registers which a programmer can directly access (of-course through the code he write) for the perfect running of the software. ... A flag byte is a generic term for a byte used to indicate conditions within a binary computer. ... A status register is a collection of flag bits for a microprocessor that indicates the status of various mathematical operations. ...

External Links

• Cracking Open The Pentium III
• Intel® IA-32 Architecture Software Developer Manuals (recommended)
• AMD64 Architecture Tech Docs