Buses are systems that transfer data between computer components like the CPU, memory, and expansion cards. The main types of buses are the front-side bus between the CPU and memory, and expansion buses like PCI and PCIe that connect add-on cards. Buses reduce the number of pathways needed to connect components by using a single channel. Faster buses allow for higher bandwidth and improved performance. Newer standards like PCIe use point-to-point connections to avoid bottlenecks and enable much faster data transfer rates compared to older bus architectures.

1. Buses
By: Kyle Kowalski and Matt
Levandowski

2. What is it
● A Bus is a system that moves data from one
source to another
● First implementation was in early
computing with a System bus

3. Why is it needed
● The purpose of buses is to reduce the
number of "pathways" needed for
communication between the components,
by carrying out all communications over a
single data channel. This is why the
metaphor of a "data highway" is sometimes
used.
● Synchronization between components
● HIGH speed transfer between
CPU/CPU/MEMORY

4. Characteristics
We measure data transfer by two metrics:
1. Total number of bits we can transfer in
parallel. This is called the width of the data.
2. The clock rate or frequency (in Hertz) of
the bus
Each time data is sent or received is
considered one cycle

5. Total Transfer Speed: Bandwidth
A bus with a width of 16 bits and a frequency
of 133 MHz, therefore, has a transfer speed
equal to:
● 16 * 133.106 = 2128*106 bit/s,
● or 2128*106/8 = 266*106 bytes/s
● or 266*106 /1000 = 266*103 KB/s
● or 259.7*103 /1000 = 266 MB/s

6. BUS Timeline
● 1982 - ISA by IBM - 4.77 MB/s (8 bits wide at
4.77 MHz)
● 1988 - Standard Architecture (EISA) - 33.32
MB/s (32 bits at 8 MHz)
● Early 90's - PCI Peripheral Component
Interconnect - 133MB/s (32-bit at 33 MHz)
● Mid 90's - USB 1.0 1.5 MB/sec
● 2000 - USB 2.0 60 MB/sec
● 2010 - USB 3.0 500 MB/sec
● 2011 - PCI Express 3.0: 31.5 GB/s

7. Usually two main buses in a PC
The internal bus
(sometimes called
the front-side bus or
FSB for short or the
system bus).
The expansion bus
(sometimes called
the input/output bus
or the control bus)

8. Front Side Bus or System Bus
● A Standard CPU system
bus is comprised of a
Control bus, an Address
bus and a Data bus.
● The FSB can range from
speeds of 66 MHz, 133
MHz, 100 MHz, 266 MHz,
400 MHz, and up.
● Most CPU today add a
third bus known as an
Expansion bus.

9. Expansion Bus
● Used to add additional expansion cards into
the CPU.
● Comes in Internal and External
● Common internal buses are PCI, PCI express
and SATA
● Common external buses are USB, CAN and
IEEE 1394(Firewire)

10. New Motherboard Design

11. Chipsets
● The Northbridge is an integrated circuit (e.
g.,Intel orVIA) that is responsible for
communications between the CPU
interface,AGP,PCI, and the memory. The
Northbridge gets its name for commonly
being North of the PCI bus.
● The Southbridge is responsible for the hard-
drive controller, I/O controller and
integrated hardware such as sound card,
video card if present on the motherboard,
USB, and Ethernet.

12. How it Works an overview
When the CPU needs data
from RAM, a request is sent to
the Northbridge memory
controller. After the request
has been received, it
responds with how long the
processor will need to wait in
order to read the memory
over the front side bus(FSB).
Some newer motherboards
have replaced the

13. Multipliers
● In computing a multiplier, CPU multiplier,
clock ratio, clock multiplier, CPU Core Ratio
is the speed ratio between the CPU and the
FSB.
● For example, a CPU with a multiplier of 20
and an external clock of 133 MHz will have
a CPU speed of 2.66GHz.
● Memory often has a multiplier to it which
some BIOS let you tweak for different
performance.

14. Overclocking
● CPU speed is generally calculated by a bus
speed (often called the FSB) and a
multiplier.
● Multiply these together and you get the
actual speed the CPU runs at. The bus
speed is typically the speed that other
components (such as the memory) in a
system run at.
● You overclock your CPU by increasing one or
the other or both. Bus speed tends to have
the best effect so if possible people will

15. Overclocking (continued)
Even though the CPU is at the same speed the computer
will be MUCH faster with a 200MHz bus then with a
100MHz bus. This is because the bus is what carriers the
data to and from the CPU, the faster you make the bus
the less of a bottleneck it becomes. The CPU no longer
has to wait as long for the next instruction.
Just make sure to have better cooling, and you need to
have more voltage going to the components (CPU and
chipsets)

16. PCI Express Why it's so fast
Each lane of a PCI Express
connection contains two pairs of
wires -- one to send and one to
receive. Packets of data move
across the lane at a rate of one bit
per cycle. A x1 connection, the
smallest PCIe connection, has one
lane made up of four wires. It
carries one bit per cycle in each
direction. A x2 link contains eight
wires and transmits two bits at
once, a x4 link transmits four bits,
and so on. Other configurations are
x12, x16 and x32.

17. PCI Express How it works
● Prioritization of data, which
allows the system to move the
most important data first and
helps prevent bottlenecks
● Time-dependent (real-time) data
transfers
● Better handshaking and error
detection
● Each device has its own
dedicated, point-to-point
connection to the switch, signals
from multiple sources no longer
have to work their way through
the same bus.

18. References
http://www.d-silence.com/feature.php?id=237
http://en.kioskea.net/contents/pc/bus.php3
http://arstechnica.com/features/2004/07/pcie/
http://old.pinouts.ru/Slots/
http://www.hardwaresecrets.com/article/Everything-You-Need-to-Know-About-the-PCI-Express/190/3
http://www.waste.org/~winkles/hardware/pci.htm
http://dangerousprototypes.com/docs/Bus_Pirate
http://www.cpushack.com/cpu-overclocking.html
Tyson, Jeff, and Ed Grabianowski. "How PCI Works" 02 May 2001. HowStuffWorks.com. <http://computer.
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