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Operands are also represented symbolically. For example, the instruction


may mean add the value contained in data location Y to the contents of register R. In this example. Y refers to the address of a location in memory, and R refers to a particular register. Note that the operation is performed on the contents of a loca­tion, not on its address.

Simple Instruction Format

1.3 instruction types

Consider a high-level language instruction that could be expressed in a language such as BASIC or FORTRAN. For example,

X = X+Y

This statement instructs the computer lo add the value stored in Y to the value Stored in X and put the result in X. How might this be accomplished with machine instructions? Let us assume that the variables X and Y correspond lo locations 513 and 514. If we assume a simple set of machine instructions, this operation could be accomplished with three instructions:

1. Load a register with the contents of memory location 513.

2. Add the contents of memory location 514 to the register.

3. Store the contents of the register in memory location 513.

As can be seen, the single BASIC instruction may require three machine instructions. This is typical of the relationship between a high-level language and a machine language. A high-level language expresses operations in a concise algebraic form, using variables. A machine language expresses operations in a basic form involving the movement of data to or from registers.

With this simple example to guide us, let us consider the types of instructions that must be included in a practical computer. A computer should have a set of instructions that allows the user to formulate any data processing task. Another way to view it is to consider the capabilities of a high-level programming language. Any program written in a high-level language must be translated into machine language to be executed. Thus, the set of machine instructions must be sufficient to express any of the instructions from a high-level language. With this in mind we can cate­gorize instruction types as follows:

  • Data processing: Arithmetic and logic instructions
  • Data storage: Memory instructions
  • Data movement: I/O instructions
  • Control: Test and branch instructions

1.4 number of addresses

What is the maximum number of addresses one might need in an instruction? Evidently, arithmetic and logic instructions will require the most operands. Virtually all arithmetic and logic operations are either unary (one operand) or binary (two operands). Thus, we would need a maximum of two addresses to reference operands. The result of an operation must be stored, suggesting a third address. Finally, after com­pletion of an instruction, the next instruction must be fetched, and its address is needed.

This line of reasoning suggests that an instruction could plausibly be required to contain four address references: two operands, one result and the address of the next instruction. In practice, four-address instructions are extremely rare. Most instructions have one, two, or three operand addresses, with the address of the next instruction being implicit (obtained from the program counter).

Questions & Answers

how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Computer architecture. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10761/1.1
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