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One more component is needed. An input device will bring instructions and data in sequentially, but a program is not invariably executed sequentially: it may jump around. Similarly, operations on data may require access to more than just one element at a lime in a predetermined sequence. Thus, There must be a place to store temporarily both instructions and data. That module is called memory, or main memory to distinguish it from external storage or peripheral devices. Von Neumann pointed out that the same memory could be used to store both instructions and data.

Figure 2 illustrates these top-level components and suggests the interactions among them. The CPU exchanges data with memory. For this purpose, it typically makes use of two internal (to the CPU) registers: a memory address register (MAR), which specifies the address in memory for the next read or write, and a memory buffer register (MBR), which contains the data to be written into memory or receives the data read from memory. Similarly, an I/O address register (I/OAR) specifies a particular I/O device. An I/O buffer register (I/OBR) is used for the exchange of data between an I/O module and the CPU.

A memory module consists of a set of locations, defined by sequentially num­bered addresses. Each location contains a binary number that can be interpreted as either an instruction or data. An I/O module transfers data from external devices to CPU and memory, and vice versa. It contains internal buffers for temporarily hold­ing these data until they can be sent on.

Having looked briefly al these major components, we now turn to an overview of how these components function together to execute programs.

Figure 2 Computer components: Top-level view

2. computer function

The basic function performed by a computer is execution of a program, which con­sists of a set of instructions stored in memory. The processor does the actual work by executing instructions specified in the program. In its simplest form, instruction processing consists of two steps: The processor reads (fetches) instructions from memory one at a time and executes each instruction. Program execution consists of repeating the process of instruction fetch and instruction execution. The Instruction execution may involve several operations and depends on the nature of the instruc­tion.

The processing required for a single instruction is called an instruction cycle. Using the simplified two-step description given previously, the instruction cycle is depicted in Figure 3

Figure 3: Basic instruction cycle

The two steps are referred to as the fetch cycle and the execute cycle. Program execution halts only if the machine is turned off, some sort of unrecoverable error occurs, or a program instruction that halts the computer is encountered.

2.1 instruction fetch and execute

Fetch cycle:

  • Program Counter (PC) holds address of next instruction to fetch
  • Processor fetches instruction from memory location pointed to by PC
  • Increment PC (Unless told otherwise)
  • Instruction loaded into Instruction Register (IR)
  • Processor interprets instruction and performs required actions

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Good
with the given example MOV BX,AX describe the sequence that will be followed using instruction state diagram
Gireesh 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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