The commands that specify the basic operations of the computer are called the instruction system. The instruction system is the language system of computer hardware, also called machine language. It refers to the collection of all instructions possessed by the machine. It is the main interface between software and hardware and reflects the basic functions of the computer.
From the perspective of system structure, it is the main attribute of the computer seen by the system programmer. (Recommended learning:PHP Video Tutorial)
Therefore, the instruction system represents the basic functions of the computer, determines the capabilities required by the machine, and also determines the format of the instructions and the structure of the machine.
Designing the instruction system is to choose whether some basic operations in the computer system (including operating systems and high-level languages) should be implemented by hardware or software, and whether certain complex operations should be implemented by a dedicated instruction , is still implemented by a series of basic instructions, and then specifically determines the instruction format, type, operation and access method of the operands of the instruction system.
The performance of the instruction system determines the basic functions of the computer, and its design is directly related to the computer's hardware structure and user needs.A complete instruction system should meet the following four requirements:
1. Completeness
refers to the instruction system when writing various programs in assembly language. The instructions provided directly are sufficient without having to implement them in software. Completeness requires that the command system be rich, fully functional, and easy to use.
2, Effectiveness
means that programs written using this instruction system can run efficiently. High efficiency is mainly reflected in the small storage space occupied by the program and the fast execution speed.
3. Regularity
includes the symmetry, uniformity, instruction format and data format consistency of the instruction system. Symmetry means that all registers and memory units in the instruction system can be treated equally, and all instructions can use various addressing modes;
Uniformity means: an instruction of an operational nature Various data types can be supported; the consistency of the instruction format and the data format means that there is a certain relationship between the instruction length and the data length to facilitate processing and access.
4, Compatibility
At least it must be "upward compatible", that is, software running on low-end machines can run on high-end machines.
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