What are registers?
Registers are temporary memory units that store
words. The registers are located in the
processor, instead of in RAM, so data can be
accessed and stored faster. The eight registers in our example are called
PC, AC, IR, TIR, +1, AMASK, MAR, and MBR, and are used as follows:
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Index and Glossary]
Program Counter. Stores the address of the
Accumulator. Stores a previously calculated value or a value loaded from
the main memory.
Instruction Register. Stores a copy of the instruction loaded from main
Temporary Instruction Register. As the CPU evaluates exactly what an
instruction is supposed to do, it stores the edited instruction in the
A constant that represents the number one. The CPU cannot access a number
unless it is in a register or loaded from main memory, or somehow
computed. Therefore this register is set aside to represent this often
Address Mask. When the CPU needs to know the address of a target word that
an instruction is using, the AMASK is AND'ed with the instruction to
eliminate the opcode, leaving only the
desired address. If that didn't make sense, leave it to the discussion of
macro-instructions later on.
Memory Address Register. This register contains the address of the place
the CPU wants to work with in the main memory. It is directly connected
to the RAM chips on the motherboard.
Memory Buffer Register. This register contains the word that was either
loaded from main memory or that is going to be stored in main memory. It
is also directly connected to the RAM chips on the motherboard.
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