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The second peculiarity: everything what may be done on the machinery language, may be done in the Assembly Language as well.

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Programming in the Assembly Language is much more easier than in the machinery (digital) one, because in the Assembly they use symbolic names instead of binary.

Bijectional correspondence between propositions of the Assembly Language and machinery instructions is the first peculiarity of the Assembly Language, which distinguishes it from high-level languages.

The second peculiarity: everything what may be done on the machinery language, may be done in the Assembly Language as well.

The third peculiarity: a program written in the Assembly Language can work on computers of one family only (i.e. The Assembly Language is machine dependable)

Programming in the Assembly language directly depends upon the apparatus possibilities of the microprocessor. The first computers of the IBM corporation were equipped with 16-th width counting unit and from the beginning with the 8-th width system bus, but soon they became the 16-th width on the whole. These microprocessors worked in so called real address mode, which is characterized by: 1) addressing only to 1Mbyte of main memory; 2) single-tasking operating system (Real—time operating System (RTS)).

*Now there are some more modes of microprocessor work:

- protected mode (it is characterized by possibility of addressing up to 64 Giga bytes);

- virtual 8086 mode (it is characterized by possibility of the processing a number of programs simultaneously), the transition to this mode is possible if microprocessor has been working in the protected mode;

- system control mode (this mode provides the operational system with mechanism for execution machinery dependable functions).



Why it is necessary to study the Assembly Language?


There are two reasons for writing programs in the Assembly Language: performance and an access to the machine. High-skilled programmers may write programs in the Assembly, which work rather quicker than those written in high-level languages (drivers and BIOS procedures are such programs) Some of procedures demand a direct access to the hardware, and they are written in the Assembly, there is no high-level languages in which it will be possible to write such kind of procedures.

**The first reason to work with assembler is that it provides the opportunity of knowing more about operations of your PC, it allows the development of software in a more consistent manner.

The second reason is the total control of the PC which you can have with the use of the assembler.

Another reason is that the assembly programs are quicker, smaller, and have larger capacities than ones created with other languages.

Lastly, the assembler allows an ideal optimization in programs, be it on their size or on their execution.

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