The major laptop design paradigm,
The major subsystems of laptops,
The technical details of the subcomponents,
Know the terminology and differences between desktops and laptops
The student will become familiar with the various technologies that are employed in laptops including those that have influenced desktop design. The student will be able to describe these technologies and be able to approach a mobile PC with a basic general understanding of how they work.
There is some confusion over what machine was the first laptop/notebook computer because some of the contenders are not IBM PC compatible including IBM’s PC Jr. Compaq’s first machine was a portable but it was a heavy piece of luggage that did not resemble the laptop/notebook at all.
As soon as truly portable PC technologies emerged like the new 3 ½” 720KB floppy disk drives and the new 3 ½” hard drive technologies much smaller portables followed them into the market. The Compaq Portable III and Portable 386 are notably smaller and use plasma panel displays but they are still PC’s in a suitcase style units. The IBM PC Convertible appears to be the first fully compatible portable that any user would refer to as a laptop on sight:
This PC took full advantage of the available portable technologies including the aforementioned 3 ½” drives and featured a large Liquid Crystal Display panel which could fold down over the keyboard. The entire unit weighed 13 pounds which was less than the first hard drive alone.
This laptop also featured an internal rechargeable battery on which it could function for a short session (by today’s standards) before having to recharge it. There are four types of laptop battery:
|NiCad – Nickel – Cadmium rechargeable battery technology was used in the first laptops. These are the batteries that suffer from “memory.” They must be fully discharged before they are recharged or they will not fully recharge. Also NiCads can be recharged up to 1500 times and have an excellent shelf life while charged.|
|NiMH – Nickel Metal – Hydride rechargeable batteries last 30% longer than NiCads but can only be recharged about 500 times. They are much less sensitive to “memory” effects so they do not have to be fully discharged in order to be recharged. NiMH batteries take about twice as long to recharge. NiMH batteries are now found mostly on low end systems.|
|Li-ion – Lithium Ion batteries. Older Lithium Ion batteries had experienced explosions. The new design as greatly reduced this danger. Li-ion batteries have longer lives than either NiCad or NiMH batteries and can be recharged up to 1000 times. They hold their charge better than the other types as well. Li-ion batteries can not overcharge. Li-ion batteries require special recharger circuitry and cannot be used in systems designed for NiCad or NiMH batteries which are interchangeable. Putting Li-ion batteries into these systems can result in a fire. Li-ion batteries are now the industry standard for laptops except the very low end systems.|
|LIP – LiPoly – Lithium Ion Polymer. LiPoly batteries are formed into a polymer plastic sheet that can be as thin as 1mm and assume any shape. They have 4 times the energy density of NiCads at 1/5 of the weight. They are virtually immune to “memory” effects that plague NiCads and can adversely affect the performance of the other types to some degree and Li-Polys have a life expectancy as much as 40% greater than Li-ion batteries. Since they can assume any shape and are so light they are ideal for laptops and will continue emerging as the battery of choice for these systems. They can form a sheet behind the LCD display or even sections of the case which is ideal for laptop designers, LiPolys are still somewhat expensive and are only seen in high end laptops.|
While the IBM PC Convertible used the 8088 processor and featured 512KB RAM standard, Toshiba would introduce the T1000 the following year featuring a 286 processor. Compaq already released the Portable 386 which was a small briefcase style portable. The 386SL however would be the first processor inspired by these machines to incorporate features specifically aimed at the manufacture of laptop PCs including the SMM or System Management Mode interrupt though this is formally a part of the 486SL it began in the 386SL. All 386s were manufactured from Bipolar CMOS (BiCMOS) which has a dramatically lower power consumption than previous processor manufacturing materials. The 386SL takes full advantage of this in its design. The SMM features an implementation which will trigger the System Management Interrupt. In the BIOS this can then be used to power down peripherals such as the hard drive to further save battery power. The 386SL also features a cache manager for 16-64KB of high speed external cache on the motherboard.
The 386SL would be the first in a long series of processors designed specifically for mobile computers including but certainly not limited to the 486SL, Mobile Pentium (P5x generation), and beyond. Pentium packages include the Tape Carrier Package – very small and the leads to the die are a thin plastic film mated to a thin metal film and the die itself, micro FC-PGA (a small Flip-Chip), BGA – Ball Grid Array where the connectors are little balls instead of pins, micro FC-BGA – a small Flip chip with a ball grid array on the bottom. Here is a Processor module (left) and a Mini-cartridge processor package (both mobile Pentium II’s:
The processor module contains the north bridge chipset and L2 cache as well as the processor itself. The Mini-cartridge Package is a smaller unit that contains fewer components and is also easily exchanged with another one so upgrades are possible. With the module upgrades are more difficult because part of the motherboard circuitry is built in to the processor module.
One of the main issues in the design of laptops is that most systems abound with proprietary components. This simply means that the system will not accept a standard generic component but only one made specifically for that system by the OEM – Original Equipment Manufacturer. Components can be made proprietary by making them physically different so that generic units will not fit, or they can be made logically proprietary meaning that a generic component will fit but will not function.
Motherboard manufacturing strategies are much different in mobile PCs than they are in desktops from the beginning. All components are soldered directly to the motherboard and the printed circuit etchings have been reworked to conserve space. As a result of this the expandability of a laptop left much to be desired. Even the RAM chips were directly soldered to the motherboard in many systems and the cases simply do not have the room to accommodate SIMM or later DIMM modules.
This led to the development of the SODIMM or Small Outline Dual Inline Memory Module which has the capacity and circuitry of a normal DIMM but in a smaller module:
This by the way is a 256MB DDR SODIMM module. The standard SODIMM slot is 144-pin as opposed to the 168-pin DIMM and the pins are much finer than in the DIMM. However, this standard is not strictly adhered to and many systems use proprietary slots and modules that are only available from the original manufacturer and cost much more than standard components. Many systems do use the SPD (Serial Presence Detect) pins of the module and if the module does not identify itself with a specific ID then the motherboard will refuse to recognize the module.
Quite often BIOS batteries are not included in the design of the laptop motherboard because the entire system is usually running off of a battery or at least has one available any way. So the main battery is often used as the BIOS battery. In some cases the BIOS battery consists of a large capacitor that can provide for perhaps a week of reserve energy to power the CMOS RAM chip. In order to clear up a problem that requires clearing the CMOS RAM it might be necessary to remove the main battery and then boot the system. But no work should be attempted on any laptop without sufficient experience in working on desktop systems and sufficient technical manuals for the unit being serviced.
The laptop expansion bus was originally called PCMCIA – Personal Computer Memory Card International Association. The bus was developed because of the fact that laptops memory could not be upgraded at all or very poorly and at very high prices. As a result of this the PCMCIA bus allowed for the attachment of a small credit card sized module that could increase the total system memory. This bus evolved into a powerful universal expansion bus that can accommodate any peripheral component. The 1997 PCMCIA standards allow for:
|DMA support – A peripheral can claim this system resource if available and utilitize the 8237 DMA controller(s) or their equivalents to manage large block transfers of data to and from memory.|
|3.3v operation – the bus carries this voltage to the cards so they can run at the lower voltage and reduce heat as well as power consumption.|
|APM support – APM is the BIOS elaboration on the CPU’s SMM design. As a published standard and made available on the PCMCIA bus, any card can “hook” this protocol and respond to requests to go idle, shutdown and resume activity.|
|Plug-n-Play support – This means that the bus cooperates with the system BIOS and the OS (if PnP) to notify the OS that a new device has been installed and to begin the driver installation process or it can notify the OS that it has been removed and to deactivate the drivers.|
|PCMCIA was incorporated by the ATA-2 standard. The bus supports ATA which means that hard drives can be attached directly to the bus with very little interfacing modifications and function.|
|Multifunction card support – With the 1997 standard any PCMCIA card can have more than one peripheral component built into it such as a NIC and a modem.|
|Zoomed Video Interface – a high speed pathway was built in between the PCMCIA bus and the (S)VGA bus path so that high speed video peripherals could be attached to the PCMCIA bus.|
|Thermal detection system – can warn the system if cards are reaching dangerous temperature levels.|
|CardBus – a 32 bit, 33Mhz card slot was defined to expand on the peripheral capabilities of the original bus slots. The slot and card designs are such that CardBus cards will not fit into standard PCMCIA slots.|
PCMCIA was also formally renamed PC Card, the two names refer to the same bus. CardBus refers to the new and now standard 32 bit/33Mhz version of the standard. PCMCIA was originally an 8 bit technology running on an 8.33Mhz clock cycle (the PCMCIA controller was a peripheral of the ISA bus). PC Card-16 is the 16 bit version of the bus. CardBus is a redesign that makes available to laptop expansion cards the same performance as PCI cards.
PC Cards come in three formally defined types: Type I, Type II, Type III. The dimensions are the same except for the thickness: Type I – 3.3mm, Type II – 5.0mm and Type III – 10.5mm. Type I’s are used mainly for solid state devices with no external connections (since they are so thin) such as memory expansion cards. Type II’s are used for solid state peripherals that do have external connectors such as modems and NIC’s. Type III’s are most often used for small hard drives.
Liquid Crystal Display technology was what made the true laptop possible. Cathode Ray Tube displays are far too large and heavy to be practical in portable computers even though small ones were used on the first portable PC’s which made them heavy and they had to be carried like a suitcase. LCD’s depend on an interesting physical property. The LCD consists of a cell in which specifically designed large molecules (called super twist nematics) float in a liquid. When an electrical current is applied to the cell so that the current flows through the liquid, the molecules change their form:
The key to how this works is the use of polarized light. Light is polarized if it passes through a filter that only allows light waves traveling in a certain orientation to pass through it.
The wave that passes through the polarization filter is aligned with the vertical slit. The red wave is aligned with the red line and not with the slit and so does not pass through the filter and on into the LCD cell. Once the light source has been polarized, the waves then pass through the LCD. They pass unimpeded if there is no current and the molecules are floating about randomly. In the LCD cell, the molecules arrange themselves so that the polarized light can either pass through unimpeded or gets blocked when the cell is charged.
The first LCDs were monochrome and depended on this simple physical phenomenon of LCD technology. Obviously an LCD is dim because all light waves that are not oriented with the polarizing filter get blocked completely out of the effect (only a small percentage of light waves will be aligned with the slit). Furthermore the LCD is slow. It takes time for all of the molecules to flow into new shapes and positions when the current is applied, and only the molecular vibrations of the ambient temperature force them back to randomness when the current is dropped. With color designs the cells are arranged in triplets each with a color filter as well as a polarizing filter each triplet has a red cell a green cell and a blue cell. The intensity of each color is controlled by the amount of polarization or alignment of the liquid crystal.
The two major categories of LCD are passive and active matrix displays. In passive matrix displays there is a row transistor and a column transistor. When a particular row transistor turns on and a particular column transistor turns on then current arrives at a particular cell within the matrix. Since liquid crystals have a reaction time, they can be strobed or sent a short pulse of current repeatedly rather than a continuous specific voltage in order to establish a certain amount of crystalline orientation. The row and column transistors switch in order strobing each cell with the current needed for it to assume the desired opacity (opaque – blocks light, opposite of transparent). Passive matrix cells have a low reactivity because they depend on this property for the strobing to work. They are usually very dim and have a limited viewing angle as well. Animation is extremely difficult to view on them because of the low reactivity of the cells. Passive matrix displays in two major varieties: normal and dual scan. In dual scan the screen is divided in half each with a separate set of strobing transistors. This allows each half to be more reactive and somewhat brighter as well.
The main technologies employed in passive matrix displays are then CSTN – Color Super Twist Nematic. The original passive matrix display with row and column transistors controlling the brightness of color filtered liquid crystal triplets. DSTN – Dual scan Super Twist Nematics which divide the screen in half (vertically or horizontally) improving performance, and HPA – High Performance Addressing in which cells are no longer strobed in blind order across the rows and columns but in order as needed based on changes in intensity or brightness levels. This does improve the performance of the screen in terms of reactivity and brightness but they are still inferior.
Active matrix displays have a transistor dedicated to each cell and therefore have a much higher manufacturing cost, but the cells can have very short reaction times since they do not have to be strobed which in effect reminds them periodically of their opacity level and each cell must “remember” this level between strobes. It remembers the level simply by being sluggish to change. In active matrix displays this sluggishness can be eliminated making each cell as responsive to the current level applied to it as possible. Active matrices are now capable of responses measured in milliseconds meaning that they can support full graphics animation. They are much brighter and have better viewing angles than any of the passive matrix displays. When shopping for laptops you will find that all of the low end systems have a form of passive matrix display, these days they are all HPA displays. You will find all of the high end systems have active matrix displays and it is difficult to find a unit that has a low end processor and features but with an active matrix display which is the only component worth serious upgrading (versus amount of RAM or HDD size).
The most common active matrix technology is called TFT – Thin Film Transistor referring to the fact that the entire display is manufactured as a dense array of thin film transistors up to three per cell (one for each of the triplet colors). Each transistor is designed to function like an LED – Light Emitting Diode. Each transistor is strobed from a row and column selector transistor like the passive matrix, the difference is that the transistor set for each pixel is turned on or off by the selector and stays on or off at the desired level. Only changes are sent to each pixel, otherwise they will stay activated by the dedicated transistors at the desired level. This is why the STN molecules can be designed to have the highest reactivity possible.
Hard drives for the laptop have also developed separately of those intended for desktops. There is an extension to the ATA standard that covers these drives. The standard laptop HDD is in a 2 ½” form factor with the following thicknesses: 8.4mm, 9.5mm, 12.5mm, 12.7mm, and 17.0mm. Especially large differences it may not be possible to exchange one size for the other due to the design of the HDD bay within the laptop’s frame. The drives are IDE but they have a different connector arrangement:
Pins 1 to 40 are identical to the desktop IDE interface. Pin 20 is unused as it is in the desktop IDE interface which also omits it sometimes. Pin 41 provides the +5VDC of the standard power connector of a desktop drive to the circuitry, Pin 42 provides +5VDC to the motors, Pins 43 provides power ground and Pin 44 is also unused. Pins “A” to “D” are wired in the connector to provide the jumper setting for the drive.
What single component really separated the laptop from other early portables?
What are the two main categories of LCD used for laptops?
List and describe are the three types of passive matrix LCD?
What is the form of active matrix display found on most low-end systems? Most High-end systems?
Give the first name for the laptop’s expansion bus (acronym - spelled out):
What is the primary feature of all laptops that makes them much more difficult to work on than desktop PC's?
Give the later name of this same bus, and the new laptop bus. Give their speed/width/throughput:
Explain the difference between a physically proprietary component and a logically proprietary component? Can a device be either without being the other? Can a device be both?
On a separate sheet describe the various LCD technologies. List the various mobile processor packages and their primary features. List the differences between a normal memory module and a laptop memory module. List the differences between the standard IDE interface to an HDD and the standard IDE interface for laptop HDDs. List the major battery technologies and their main features and differences.
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