Test register
Encyclopedia
A test register, in the Intel 80486
processor, is a register used by the processor, usually to do a self-test. Most of these registers are undocumented, and used by specialized software. The test registers were named TR3 to TR7. Regular programs don't usually require these registers to work. With the Pentium
, the test registers were replaced by a variety of model-specific registers (MSRs).
Two test registers, TR6 and TR7, were provided for the purpose of testing. TR6 was the test command register, and TR7 was the test data register. These registers were accessed by variants of the MOV
instruction. A test register may either be the source operand or the destination operand. The MOV instructions are defined in both real-address mode and protected mode
. The test registers are privileged resources. In protected mode, the MOV instructions that access them can only be executed at privilege level
0. An attempt to read or write the test registers when executing at any other privilege level causes a general protection exception.
Intel 80486
The Intel 80486 microprocessor was a higher performance follow up on the Intel 80386. Introduced in 1989, it was the first tightly pipelined x86 design as well as the first x86 chip to use more than a million transistors, due to a large on-chip cache and an integrated floating point unit...
processor, is a register used by the processor, usually to do a self-test. Most of these registers are undocumented, and used by specialized software. The test registers were named TR3 to TR7. Regular programs don't usually require these registers to work. With the Pentium
P5 (microarchitecture)
The original Pentium microprocessor was introduced on March 22, 1993. Its microarchitecture, deemed P5, was Intel's fifth-generation and first superscalar x86 microarchitecture. As a direct extension of the 80486 architecture, it included dual integer pipelines, a faster FPU, wider data bus,...
, the test registers were replaced by a variety of model-specific registers (MSRs).
Two test registers, TR6 and TR7, were provided for the purpose of testing. TR6 was the test command register, and TR7 was the test data register. These registers were accessed by variants of the MOV
MOV (x86 instruction)
In the x86 assembly language, the MOV instruction is a mnemonic for the copying of data from one location to another. The x86 assembly language has a number of different move instructions...
instruction. A test register may either be the source operand or the destination operand. The MOV instructions are defined in both real-address mode and protected mode
Protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units...
. The test registers are privileged resources. In protected mode, the MOV instructions that access them can only be executed at privilege level
Privilege level
A privilege level in the x86 instruction set controls the access of the program currently running on the processor to resources such as memory regions, I/O ports, and special instructions. There are 4 privilege levels ranging from 0 which is the most privileged, to 3 which is least privileged...
0. An attempt to read or write the test registers when executing at any other privilege level causes a general protection exception.