Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. 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. Usually, regular programs don't 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.

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