Buses What is a bus? an electronic traffic lane through which
electrical signals are carried from one chip to another chip most
often used in the context of communication between the processor
and other system components there are many different kinds of bus
including ISA, EISA, MCA,SCSI and the local bus standards PCI and
VL-Bus quoted from www.pctechguide.com CSCI1412-HW-54
Slide 5
A Potential Birds Nest Imagine connecting four chips to each
other CSCI1412-HW-55 Now try to imagine what would happen with
twenty chips!
Slide 6
The Bus Solution A bus comprises the actual physical components
(wires, connectors, chips) and a set of protocols defining how it
is used (timing, access methods) CSCI1412-HW-56 the busslots for
extra peripherals
Slide 7
The System Bus The connection between the microprocessor and
RAM is the most important bus it is made up of three component
buses which are collectively known as the system bus or Front Side
Bus address bus (location of memory) data bus (values to / from
memory) control bus the system bus is now 64 bits wide 64 wires in
parallel runs at speeds up to 1600 MHz on an Intel i7 short,
delicate, single purpose CSCI1412-HW-57
Slide 8
The ISA bus The ISA (Industry Standard Architecture) bus was
incorporated in the first IBM PC standard used to attached to
peripherals and the expansion slots originally 4.77 MHz, now 8 MHz
now 16 bit it was the fact that it was published as an open
standard and was flexible enough to connect a wide variety of
expansion cards that was the main reason for the success of the IBM
PC still used today, although Intel and Microsoft have decreed that
it is to be abolished CSCI1412-HW-58
Slide 9
EISA / MCA As the ISA bus was so slow (and because it was a
fixed standard), there were some attempts to improve or enhance it
MCA (Micro Channel Architecture) from IBM 32 bit, 10 MHz
incompatible with ISA and not supported by Intel/MS therefore died
out! EISA (Extended ISA) 32 bit, 8 MHz extended (32 bits v. 16) but
still compatible successful for a while, but now superceded
CSCI1412-HW-59
Slide 10
PCI Intel created a new standard: PCI (Peripheral Component
Interface) 32 bit or 64 bit, originally 33Mhz, now 66 MHz fixed,
independent of processor speed robust, upgradeable, reliable,
compatible plug and play Intel and MS defined a specification to
allow peripherals to be automatically detected and configured by
the PC, rather than by the user In Express format now the standard
for high speed peripherals hard disk and graphics controllers
CSCI1412-HW-510
Slide 11
SCSI / SCSI-2 The SCSI (Small Computer System Interface) bus
was defined by ANSI in 1986 used widely in non IBM-PC (esp. UNIX,
Macs) originally designed for hard disk drives, now extended to CD-
ROMs, scanners, faxes, etc SCSI-1: 8 bit, SCSI-2: 16 bit can be
incorporated into PCs using a SCSI card commands issued at a higher
level e.g. use logical block address (not physical location) SCSI
devices need termination with resistors jumper connections on SCSI
device CSCI1412-HW-511
Slide 12
AGP and PCI Express AGP used on older PCs for graphics - AGP 8x
2,100 MB/s Peripheral Component Interconnect Express - PCI
Express,a standard for graphics applications (replacing AGP)
Sometimes called PCI-E or PCIe Developed by Intel in 2004 PCI
Express is serial and can transmit data in two directions at the
same time. PCI is parallel and can only transit in one direction.
Communication via lanes, each lane is a unidirectional point to
point serial link Physical PCIe slots may contain 1-32 lanes in
powers of 2, e.g. 1,2,4,8,16,32. Data is interleaved - successive
byte are sent down successive lanes. CSCI1412-HW-512
Slide 13
PCIe - 1 In PCIe 1.1 released in 2004 each lane carried 250
MB/s PCIe 2.0 released in late 2007 500MB/s PCIe 3.0 due for
release in 2010 1 GB/s As the number of lanes increase the transfer
rate increases PCI Express 1x 250 [500] MB/s PCI Express 2x 500
[1000]MB/s PCI Express 4x 1000 [2000] MB/s PCI Express 8x 2000
[4000] MB/s PCI Express 16x 4000 [8000] MB/s PCI Express 32x 8000
[16000] MB An 8-lane PCIe 2.o carries as much as the fastest AGP
CSCI1412-HW-513
Slide 14
PCIe - 2 All new graphics cards are now PCIe NVIDIA uses PCIe
in its Scalable Link Interface (SLI) technology, to allow multiple
graphics cards of the same chipset and model number to be run in
tandem. ATI also has developed a multi-GPU (Graphics Processing
Units) system based on PCIe called CrossFire. AMD and NVIDIA
released motherboard chipsets which support up to four PCIe x16
slots, allowing tri-GPU and quad-GPU card configurations.
CSCI1412-HW-514
Slide 15
PCMCIA The PCMCIA (Personal Computer Memory Card International
Association) is both an organisation and a standard for the
expansion of portables (laptops, handhelds, etc) loose
collaboration of hardware and software industries rather than a
single organisation originally a 16 bit standard, now 32 bit not
really a true bus, more of a total interface specification
including hardware design and software services can handle RAM,
disks, graphics very flexible, generic, handles hot-swapping
CSCI1412-HW-515
Slide 16
USB - 1 The problem Many different types of ports: serial
ports, parallel ports, keyboard and mouse connections, joystick
ports, midi ports etc. Requirements A way of connecting large
numbers of devices. To replace legacy ports. Does not require
specific interrupt resources Hot-pluggable. Plug and Play. The
Universal Serial Bus (USB) developed as a solution Specification
developed by Compaq, Intel, Microsoft and NEC, joined later by
Hewlett- Packard, Lucent and Philip. The USB Implementers Forum,
Inc as a non-profit corporation to publish the specifications and
organise further development in USB. CSCI1412-HW-516
Slide 17
USB-2 Universal Serial Bus (USB) is replacing serial ports
Three data speeds, Low Speed 1.5Mbits/s This was intended for
cheap, low data rate devices like mice. The low speed captive cable
is thinner and more flexible than that required for full and high
speed. Full Speed - 12MBit/s This was originally specified for all
other devices. High Speed 480Mbits/s The high speed additions to
the specification were introduced in USB 2.0 as a response to the
higher speed of Firewire. These speeds are the fundamental clocking
rates of the system, and as such do not represent possible
throughput, which will always be lower as the result of the
protocol overheads. CSCI1412-HW-517
Slide 18
USB - 3 USB has a 'tiered star topology' in which there is a
single host controller and up to 127 'slave' devices. Because the
address field in a packet is 7 bits long, and the address 0 cannot
be used as it has special significance. The host controller is
connected to a hub, integrated within the PC, which allows a number
of attachment points (often loosely referred to as ports).
CSCI1412-HW-518
Slide 19
USB - 4 If 127 devices is not enough ! A further hub may be
plugged into each of these attachment points. A device can be
plugged into a hub, and that hub can be plugged into another hub
and so on. M Maximum number of tiers is six. The length of any
cable from hub to device is 5 metres. Could extend up to 30m with 6
tiers. For greater distances use another form of connection such as
Ethernet. CSCI1412-HW-519
Slide 20
USB - 4 At any point in time, only the host OR one device can
be transmitting at a time. When the host is transmitting a packet
of data, it is sent to every connected device. Only one device, the
addressed one, actually accepts the data. (The others all receive
it but the address is wrong for them). One device at a time is able
to transmit to the host, in response to a direct request from the
host. CSCI1412-HW-520
Slide 21
21CSCI1412-HW-5
Slide 22
Input/Output Devices In essence input and output devices allow
us (the users) access to the bits in the computer input devices
convert information from human / analogue form into digital takes
control information from the user output devices convert
information from computer to human usable form provides control
information to the user Human computer interaction (HCI) is the
study of how we interact with computers e.g. the mouse: developed
in mid 70s by Xerox ergonomic design tries to improve our HCI
CSCI1412-HW-522
Slide 23
Keyboards The original qwerty keyboard was designed to
deliberately slow typists down mechanical typewriters couldnt keep
up! common letters put close together so that the same finger must
be used (which is slow) common letters away from home positions
(F/J) There are other arrangements of letters dvorak arranged to
enhance speed Many variations on the basic theme ergonomic styles,
such as MS natural numeric keypads, function and control keys
foreign keyboards with special keys (accents, etc)
CSCI1412-HW-523
Slide 24
How Keyboards Work The keys are arranged in a grid of wires a
key press connects vertical to horizontal this is translated into a
key number later translated by the OS into the character value
CSCI1412-HW-524 often the switches are mechanical sometimes more
basic conductive membrane different weights how hard to press
clicks v. soft feel
Slide 25
Mouse There are a wide variety of types of mouse Right and left
handed Foot operated. Virtually all have USB interface Wide
configuration of buttons (e.g. For web navigation, giving
presentations) Pseudo mice type devices e.g. Tracker balls, tracker
pens Increasingly cordless with Bluetooth interface. Virtually all
mice are optical An LED produces red light which hits a surface and
is reflected back onto a sensor. The sensor sends the image to a
Digital Signal Processor DSP for analysis. The DSP determines the
speed and degree of movement. Latest versions use a laser for
better tracking and less sensitivity to surfaces.
CSCI1412-HW-525
Slide 26
Scanners A scanner takes an image and makes a digital
representation of that image there are two main types of scanner
hand held: the user moves the scanner over the image flat bed:
image is placed on scanner: lens moves either of which can scan the
image in colour or black & white different resolutions (dots
per inch: dpi) there is a wide variety of software formats for
storing the final image JPEG, TIFF, BMP, GIF, PNG, PCX, FAX
(+more!) image processing software can manipulate & convert
CSCI1412-HW-526
Slide 27
How a Scanner Works Light is shone onto paper, and reflections
are received by light sensitive diodes CSCI1412-HW-527 pctechguide
A light source illuminates the paper placed on the scanners glass
plate: blank or white areas reflect more light The scan head moves
below the paper and receives the light reflected from the paper The
light is reflected by a series of mirrors The scanners lens passes
light onto light-sensitive diodes which translate it into
electrical current
Slide 28
Other Optical Devices Optical character recognition (OCR) is
now usually software (often bundled with scanner) coverts the bits
representing the image into a sequence of letters e.g. for a word
processor now very accurate for good quality typed characters still
quite poor at handwriting (needs training) Optical mark readers
(OMR) are often dedicated hardware scanner & software rather
than scanning the whole image, the OMR simply looks for marks in
preset positions e.g. multiple choice exams, national lottery
CSCI1412-HW-528
Slide 29
Bar Codes There are many different encoding schemes UPC
(groceries), ISBN (books), Code 39 (parcels) Readers shine a laser
at the bar code and detect the reflections received there are many
physical forms of readers wands, guns, cards, prismatic
(supermarket checkouts) CSCI1412-HW-529 Groceries (UPC) - A goods
category manufacturer code centre bar guards product code check
digit
Slide 30
Sound & Voice Recognition Many people have recognised the
fact that typing is slow and laborious. Recent developments have
made speech to text and text to speech applications more common.
Text to Speech is more easy to achieve, but voices sound
monotonous. This has been a part of MS development environments
since 2005. Speech to text is more complex. A speech to text engine
is included part of MS Visual Studio 2008 Success rate on untrained
users is about 70% Great improvements after training. Not suitable
for critical applications. CSCI1412-HW-530
Slide 31
Magnetic Devices Magnetic ink character recognition (MICR)
specially shaped letters in magnetic ink the funny looking numbers
on the bottom of cheques read directly by a special purpose scanner
Magnetic strip readers these are pervading all aspects of everyday
life credit / bank / store cards, ID cards bits are encoded as
polarities on the magnetic strip on the back of the card
CSCI1412-HW-531
Slide 32
32CSCI1412-HW-5
Slide 33
Output Devices In general output devices are conveying
information (in usable form) to the user Monitor : the screen our
main view of the computer: moving images printer Laser or ink-jet
are the dominant technologies plotter specialised type of printer,
usually for large size printing e.g. Architectural drawings
loudspeakers providing sound, e.g. speech, games
CSCI1412-HW-533
Slide 34
Sound There are two main components concerned with producing
sound from a computer sound card the sound card is the device which
turns bits of information into electrical signals to drive speakers
speakers convert electrical signals into sound (vibrations of air)
stereo: different sound out of each speaker tweeters:
high-frequency, woofers: low-frequency Unlike audio CDs there are
many different standards used for encoding sound in bits wav, midi,
mpeg, mp3 CSCI1412-HW-534
Slide 35
Summary Interface mechanisms buses: ISA / PCI, PCI Express, USB
interface cards, PCMCIA Input devices keyboards, mice, joysticks,
light pens, bar codes, magnetic card reader, OCR, scanner,
microphone Output devices VDU, printers, plotter speakers
CSCI1412-HW-535