Development of Portable Computers
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Development of Portable Computers
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Objectives:
To introduce the history and development of portable computers
Discuss the development of portable computers
Discuss PC cards and power management
Lesson:
Soon after PCs became widely used in the late 1970s, computer users recognized a
need for mobile computing to reduce duplication of work and to avoid compatibility
problems.The earliest portables were known as "suitcase luggables" because they were large,
heavy, and unwieldy.They consisted of a fairly large cabinet with a small screen, 5.25-inch floppy disk
drives, and a keyboard that doubled as a cover when the computer was stored or
carried.The luggables were powered through the mains, so they could not operate away from
a power source.The development of portables focused on reducing size and weight and advancing both
display and battery technologies.Portables were made possible by the development of nickel cadmium batteries that
supplied continuous, steady voltage and by the development of the larger and lighter
liquid crystal display (LCD) screens.The first portables weighed approximately 15 pounds.
Nowadays, portables typically weigh about 6 pounds and are approximately 2 inches
thick.Some manufacturers refer to portables as "laptops" or "notebooks".
And other manufacturers reserve the term "notebook" for portable computers of between
one and two inches and weighing less than five pounds.Generally speaking, the terms "portable", "laptop", and "notebook" are interchangeable.
Portables are often more expensive than their desktop equivalents because they are
more difficult to design and manufacture.A portable can act as desktop workstation by using a docking station.
The portable is connected to the docking station, which is connected to peripheral
devices, such as monitors, printers, and network cards.Portable design has advanced to the point that the mouse is integrated as a trackball
in the keyboard, or a touchpad, and CD-ROM and digital versatile disk (DVD) drives
can be built in.Even smaller than a portable, a personal digital assistant (PDA) - or palmtop
is an organizer for personal information, such as a name-and-address database,
a to-do list, an electronic diary, and a note taker.Data is synchronized between the PDA and a desktop computer via cable or wireless
transmission.Hardware features of a PDA include backlighting, modem, infrared serial communications,
screen size, and voice recording.And software features available for PDAs include synchronization support, personal
information management (PIM), word processors, spreadsheets, presentation software,
e-mail, web browsing, and database technology.Many PDAs run on Windows CE, which has a similar look and feel to Windows 98.
Unlike desktop PCs that use a power point, portables require batteries so that they
can be used away from accessible mains power supplies.And, because computers require a steady voltage to function, special batteries needed
to be developed for use with mobile PCs.The three types of battery used with laptops today are
nickel-cadmium (Ni-Cd)
nickel-metal hydride (Ni-MH)
lithium-ion (Li-ion)
Ni-Cds were the first batteries developed for use with laptops.
Although they work well, they have distinct disadvantages, such as requiring special
disposal treatment because they are highly toxic to the environment.Also, Ni-Cds need to be completely discharged before being recharged and can be
damaged by overcharging.Each time that a Ni-Cd is recharged before being completely discharged, it loses
rechargeability, which means that it provides less computing time with each recharge.This characteristic is known as the memory effect.
Also, Ni-Cd batteries are heat-sensitive and discharge themselves when not in use.
Improved Ni-Cd batteries Ni-MH batteries have fewer problems than the original
Ni-Cd battery in that they last longer and function well on shallowrecharges
operate for longer intervals betweenrecharging
can handle overcharging
dont have battery memory problems
Although Ni-MH batteries are less toxic to the environment than Ni-Cd batteries,
they should be disposed of safely.And they are relatively heat sensitive in that they lose power when exposed to heat.
The most recent development in battery technology is the Li-Ion battery, which is
in widespread use today.It has no memory problems, lasts twice as long as Ni-MH batteries on one charge,
and cannot be overcharged because it has an inbuilt circuit breaker.However, Li-Ion batteries have a shorter lifespan than Ni-MH batteries because they
cannot handle as much recharging.The early portables used Cathode Ray Tubes (CRT), which is the same technology used
for desktop monitors and television sets today.The CRTs used in portables proved to be too small and too heavy, so they were replaced
by neon gas plasma screens that glowed when electrically charged.However, gas plasma screens use a great deal of power and are very slow.
Liquid crystal displays (LCDs) have been in use since the 1970s in watches and calculators
and, more recently, in portable computers.Unlike CRT or gas plasma screens, they do not radiate light when charged.
Instead, they prevent light from passing through by using a system of light filters
known as polarizing filters.In the first LCDs, the fields for display were filled with liquid crystal, which
were then charged to darken them and make them visible.However, this static charging technology was limited when used with computers, so
a matrix of wires was developed in which only the specified coordinates lit up
when electrically charged.By painting tiny red, green, and blue dots above each intersection on the screen,
this passive matrix LCD technology used different voltage levels to produce different
colors of differing tones.Passive matrix LCDs are slow because they refresh one line at a time.
They were later replaced by dual-scan passive matrix LCDs, which refreshes two lines
at a time and could produce 256 colors.Then active matrix technology was developed, in which each intersection has its
own thin film transistor (TFT), which refreshes the intersection the moment the
electrical charge changes.Active matrix (TFT) screens have distinct advantages over passive matrix screens.
They are much faster and can produce 16.7 million colors.
They are also brighter, generate better contrast, and have a wider viewing area.
The processors used in mobile computing have been developed to the point that they
now equal the processing power of high-performance desktop computer processors.Examples of the high-performance processors developed specifically for notebooks
are Intel's Mobile Pentium III and Mobile Celeron processors.The Mobile Pentium III is based on SpeedStep Technology, which allows the user to
customize high-performance computing.When powered by battery, the processing frequency of a Mobile Pentium III automatically
reduces to conserve battery life.The user can increase the speed manually if needs be.
Mobile Pentium III processors incorporate 0.18 micron technology, which helped reduce
the space needed by these processors over their predecessors by a factor of 20
percent.For instance, the Mobile Pentium III is able to accommodate up to 28.1 million transistors.
Also, while earlier processors have 512K external caches, the Mobile Pentium III
256K cache is integrated with the CPU to increase access times.In the Mobile Pentium III, the Ball Grid Array (BGA), Pin Grid Array (PGA), and
module packaging contribute to notebooks being lighter and thinner.And the modular design allows for variations in size, weight, and price.
The streaming extensions supplied with the Mobile Pentium III allow for high-speed
multimedia processing over the Internet and on the hard drive.And the quality of the multimedia delivery is improved in terms of color, sound,
resolution, and smoothness of frame rates.A Mobile Celeron processor has the same microarchitecture core as a Pentium II and
includes a 128K integrated cache that accommodates over 18 million transistors.Celeron processors are based on 0.18 micron CMOS process technology.
The Celeron processors can be packaged as modules or BGA.
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