<< Chapter < Page Chapter >> Page >

The data lines (data bus):

  • Provide a path for moving, data between system modules. These lines, collectively, are called the data bus.
  • The width of the data bus: The data bus may consist of from 32 to hundreds of separate lines, the number of lines being referred to as the width of the data bus. Because each line can carry only 1 bit at a time, the number of lines deter­mines how many bits can be transferred at a lime. The width of the data bus is a key factor in determining overall system performance. For example, if the data bus is 8 bits wide and each instruction is 16 bits long, then the processor must access the memory module twice during each instruction cycle.

The address lines ( address bus):

  • Address lines are used to designate the source or destination of the data on the data bus. For example, if the processor wishes to read a word (8, 16. or 32 bits) of data from memory, it puts the address of the desired word on the address lines.
  • The width of the address bus: determines the maximum possible memory capacity of the system. Furthermore, the address lines are generally also used to address I/O ports.

The control lines (control bus):

  • Control bus are used to control the access to and the use of the data and address lines. Because the data and address lines are shared by all components, there must be a means of controlling their use. Control signals transmit both com­mand and liming information between system modules. Timing signals indicate the validity of data and address information.
  • Command signals specify operations to be performed. Typical control lines include the following:
    • Memory write: Causes data on the bus to be written into the addressed location.
    • Memory read: Causes data from the addressed location to be placed on the bus.
    • I/O write: Causes data on the bus to be output to the addressed I/O port.
    • I/O read: Causes data from the addressed I/O port to be placed on the bus.
    • Transfer ACK: Indicates that data have been accepted from or placed on the bus.
    • Bus request: Indicates that a module needs to gain control of the bus.
    • Bus grant: Indicates that a requesting module has been granted control of the bus.
    • Interrupt request: Indicates that an interrupt is pending.
    • Interrupt ACK: Acknowledges that the pending interrupt has been recognized.
    • Clock: Used to synchronize operations.
    • Reset: Initializes all modules.

Figure 12 Bus Interconnection Scheme

Multiple-bus hierarchies

If a great number of devices are connected to the bus, performance will suffer. There are two main causes:

  • In general, the more devices attached to the bus, the greater the bus length and hence the greater the propagation delay. This delay determines the time it takes for devices to coordinate the use of the bus. When control of the bus passes from one device to another frequently, these propagation delays can noticeably affect performance.
  • The bus may become a bottleneck as the aggregate data transfer demand approaches the capacity of the bus. This problem can be countered to some extent by increasing the data rate that the bus can carry and by using wider buses (e.g., increasing the data bus from 32 to 64 bit). However, because the data rates generated by attached devices (e.g.. graphics and video controllers, network interfaces) are growing rapidly, this is a race that a single bus is ulti­mately destined to lose.

Accordingly, most computer systems use multiple buses, generally laid out in a hierarchy. A typical traditional structure is shown in Figure 13. There is a local bus that connects the processor to a cache memory and that may support one or more local devices. The cache memory controller connects the cache not only to this local bus, but to a system bus to which are attached all of the main memory mod­ules.

It is possible to connected I/O controllers directly onto the system bus. A more efficient solution is to make use of one or more expansion buses for this purpose. An expansion bus interface buffers data transfers between the system bus and the I/O controllers on the expansion bus. This arrangement allows the system to sup­port a wide variety of I/O devices and at the same time insulate memory-to-processor traffic from I/O traffic.

Traditional (ISA) (with cache):

Figure 13 Traditional bus architecture

Elements of bus design

Type:

Dedicated

Multiplexed

Method of arbitration:

Centralized

Distributed

Timing:

Synchronous

Asynchronous

Bus width:

Address

Data

Data transfer type:

Read

Write

Read-modify-write

Read-after-write

Block

Questions & Answers

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
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
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
with the given example MOV BX,AX describe the sequence that will be followed using instruction state diagram
Gireesh Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Computer architecture. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10761/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Computer architecture' conversation and receive update notifications?

Ask