The arithmetic logic unit (ALU) is responsible for all logical and mathematical operations in the system. The ALU receives instructions from the control unit. The ALU can take information from memory, perform computations and comparisons, and then store the results in memory locations as directed by the control unit. An additional type of ALU, called a floating point unit (FPU) or coprocessor, which performs specialized functions such as divisin and large decimal number operations, is frequently used. Most modern microprocessors include an FPU processor as part of the microprocessor. The ALU and control unit communicate with each other and perform operations in memory locations called registers. A register is a location that is internal to the microprocessor that can be used as a scartch pad for calculations. There are two types of registers used in modern systems: dedicated registers and general purpose registers. Dedicated registers are usually used for specfic functions such as maintaining status or system controlled counting operations. General purpose registers are used for multiple purposes, typically when mathematical and comparison operations occur.
When a system malfunctions, as in the case of a Blue Screen of Death, the monitor will usually display a message and multiple numbers. There numbers are the contents of the register and other key memory locations. This information is usually not overly useful for computer technician, but it can provide a great deal of information to developer and technical support professinals as to the nature of the failure. It is a good idea to capture that information before you contact customer support.