Hard Disk Drives

Except for its size and packaging, portable hard disk drive technology is similar to desktops. EIDE (Enhanced Integrated Drive Electronics) drives are standard in portable computers with the exception of the Macintosh computer, which uses SCSI. Internal hard drives, depending on the size of the system, are typically 12.5 mm or 19 mm tall, and use 2.5-inch platters. As with memory modules, hard drives are also mounted in the system a little differently by manufacturers; this can cause upgrade compatibility problems.

Some manufacturers use a caddy to hold the drive and make connections to the system. This makes upgrading as simple as inserting a new hard disk drive into the caddy and then mounting it in the system. Other systems require purchase of a specifically designed drive, complete with the proper connections built into it. Replacing the hard drive can be much easier in many portable systems than in their desktop counterparts.

The result is that multiple users can share a single machine by simply snapping in their own hard drives. However, because laptops are specialized equipment, any servicing beyond batteries, hard drives, and memory is usually left to specialists or the manufacturer.

The support provided by the system's BIOS (basic input/output system) determines the upgradability of a system. Older systems, particularly those manufactured before 1995, might offer only limited drive-size options. BIOS chips made before EIDE hard disk drives became the standard can support a maximum hard drive size of 528 MB. A flash BIOS upgrade might be available for your system to provide additional drives. Another option for expanding hard drive space is the PC Card hard drive. This device fits into a Type III PC Card slot and can provide as much as 1-2 GB of additional space. External drives are also available and can be connected using a PC Card SCSI host or specialized parallel port drive interfaces—you can use any size SCSI drive you choose without being limited by your system's BIOS.

Memory

As with desktop systems, adding memory is one of the most common upgrades to portable computers. Unlike desktop computers, which offer only three basic types of slots for additional RAM (random access memory), there are dozens of different memory-chip configurations designed to squeeze memory upgrades into the small cases of portable systems.

Some portables use memory cartridges that look a lot like PC Cards, but they plug into a dedicated IC memory socket. Others use extender boards like SIMMs (single inline memory modules) and DIMMs (dual inline memory modules). In any case, it is strongly recommended that you only install memory modules that have been designed for your system, and only in the configurations recommended by the manufacturer. This does not necessarily limit you to products made by your system's manufacturer, however, because a number of companies manufacture upgrade modules for dozens of systems.

Portable computers use the same types of dynamic RAM (DRAM) and static RAM (SRAM) as desktops and, thanks to advances in thermal management, today's high-end portable systems usually include SRAM cache memory.

Processors

Computer CPU (central processing unit) manufacturers spend a great deal of time and effort on designing chips specifically for the portable market. In desktop systems, cooling fans housed inside the case dissipate CPU heat. There is no room for this solution in a portable system, so manufacturers have addressed this problem in the packaging of the chip itself.

Chip manufacturer Intel's solution to the size and heat problems is the Tape Carrier Package. This method of packaging reduces the size, power consumption, and heat generated by the chip. A Pentium mounted on a motherboard using Tape Carrier Packaging is much smaller and lighter than the pin grid array (PGA) used in desktop systems. The 49-mm square of the PGA is reduced to 29 mm, the thickness to approximately 1 mm, and the weight from 55 grams to less than 1 gram.

The Tape Carrier Packaging processor is bonded to a piece of polyamide film, which is like photographic film, using tape automated bonding (TAB). This is the same process used to attach electrical connections to LCD panels. The film (called tape) is laminated with copper foil etched to form the leads that connect the processor to the motherboard. When the leads are formed, they are gold-plated to protect them against corrosion, bonded to the processor chip itself, and then the entire assembly is coated with a protective resin.

After being tested, the tape is cut to the proper size and the ends are folded into a "gull wing" shape that allows the leads to be soldered to the motherboard while the processor is suspended slightly above it. A thermally conductive paste is inserted between the processor chip and the motherboard, allowing heat to be dissipated through a sink on the underside of the motherboard, keeping it away from the soldered connections. Of course, because Tape Carrier Packaging processors are soldered to the motherboard, they usually cannot be upgraded.

Some manufacturers use standard PGA processors, sometimes accompanied by fans. In addition to having a greatly reduced battery life, these systems can be too hot to touch comfortably. Always check the exact model of processor that is used in a system you intend to purchase, not just the processing speed. You might not want to purchase a non-Tape Carrier Packaging processor for the aforementioned reasons.

Screen Resolution

An LCD display's resolution is determined as much by the screen hardware as by the drivers and amount of installed video memory. Some machines with less robust screens achieve resolutions of 1024 × 600 (and even more) by using a virtual screen. This is a memory-swapping technique whereby a larger display is held in video memory while the actual screen displays the portion that fits into a 640 × 480 window. The cursor can be used to "pan" the image so that the viewable desktop is within the physical limits of the actual display.

As in regular desktop systems, color depth is affected by video memory. To operate any LCD display in 16-bit or 24-bit color mode, you must have sufficient video memory available. Portables usually have video adapter hardware permanently installed on the motherboard, which makes an upgrade of the display features virtually impossible. Most portables allow connection to an external monitor to increase video capabilities.

Active-Matrix Displays

Active-matrix displays are also known as TFTs (thin film transistors). They differ from dual-scan screens because they have a transistor for every pixel on the screen rather than just at the edges. Electrodes apply voltages at the perimeter of the grid to address each pixel individually.

Because each pixel is powered individually, generating its own light and the appropriate color, a much brighter and more vivid picture results. Creating light instead of altering reflection provides a wider viewing angle, which allows more than one viewer to see the screen at a time. The refreshes are faster and the display lacks the fuzziness associated with the dual-scan systems.

Naturally, the cost of having 480,000 transistors instead of merely 1400 (on an 800 × 600 screen) makes the active-matrix screen more expensive. It also requires a lot more power and drains batteries faster. Failure of a transistor causes individual "dead pixels," but this is far less noticeable than the black line caused by a transistor failure of the dual-scan screen.

Larger screens and higher resolutions mimicking that of desktop models have become the standard on high-end laptops. Many portable systems today also include PCI (Peripheral Component Interconnect) bus video adapters. These screens come very close to the quality of a desktop display, but lack some of the fine controls available on fixed units.

Dual-Scan Displays

The dual-scan display (also known as a passive-matrix display) consists of transistors running down the x- and y-axis of the screen. The number of transistors determines the screen's resolution. The two transistors that intersect on the x- and y-axis control each pixel on the screen.

If a transistor fails, the entire line of pixels is disabled, leaving a black line across the screen. There is no way to repair this problem except to replace the display. The term dual-scan is derived from the fact that the processor redraws half of the screen at a time, which speeds up the refresh rate a little.

Dual-scan displays are considered inferior to active-matrix screens because they tend to be dimmer. For this reason, portable computers with this technology are becoming rare. They work by modifying the properties of reflected light rather than generating their own light. They are also more prone to ghost images, and it is difficult for two people to see the screen at the same time, because these displays can't be viewed well from an angle. The standard size for this type of screen is 10.5 inches (measured diagonally) with a resolution of 640 × 480. New systems are available with 12.1-inch and larger displays that have a resolution of 800 × 600.

Portable Computer Hardware

Although many components in a portable computer are similar to those of a desktop system, some components are very different. The major difference between a portable system and desktop system is the display screen.

Displays

Portable computers have a flat LCD screen that is about .5 inch thick. The display is typically the most expensive component in a portable system. Often it is more economical to replace the entire computer than to replace the screen. An LCD display is designed to operate at a specific resolution because the size of the pixels on an LCD panel cannot be changed. On a desktop system, by contrast, the signal output from the video adapter can change the resolution on the monitor, thereby changing the number of pixels on the screen. An LCD panel should be thought of as a grid ruled to a specific resolution. Transistors control the color that is displayed by each pixel. The two major types of LCD displays used in portable systems today (dual-scan and active-matrix) are defined by their arrangement of transistors.

Computer Cards

To provide laptop and notebook computers with the same expandability associated with desktop computers, the PCMCIA (Personal Computer Memory Card International Association) established several standards for credit-card-sized expansion boards that fit into small slots on these smaller machines. These expansion boards are now commonly referred to as PC Cards. The PCMCIA standards have revolutionized mobile personal computers, providing them with the ability to add memory expansion cards, network interface cards (NICs), SCSI (Small Computer System Interface) devices, communication hardware (for instance, modems and faxes), and many other devices that were previously unavailable to laptop and notebook computer users.

Compatibility problems surfaced along with the development of the PC Card for portable computers. To overcome these incompatibilities, PCMCIA standards were created. The following table outlines the four PCMCIA types and their guidelines.

Type	Standard Description
Type I	This original computer-card standard is now referred to as the Type I standard. These slots work only with memory expansion cards. Type I cards are 3.3 mm thick.
Type II	Type II cards support most types of expansion devices (like communication hardware) or network adapters. Type II can accommodate cards that are 5 mm thick.
Type III	Type III slots are primarily for computers with removable hard disk drives. This standard was introduced in 1992. They are 10.5 mm thick; however, they are compatible with Type I and Type II cards.
Type IV	Type IV slots are intended to be used with hard disk drives that are thicker than the 10.5 mm Type III slot.

The PC Card itself is usually sealed in a thin metal case. One end contains the interface to the PC Card adapter (68 tiny pinholes); the other end might contain a connector for a telephone line, a network, or another external device.

PC Card is part of the Plug and Play standard, which means it allows you to add components without first shutting off or rebooting the computer. In short, PC Cards are not configured with jumper settings (because they don't have any) but with software.

Subnotebook (Palmtop) Computers

Even smaller than the notebook computers are subnotebook computers, also known as palmtops or handhelds. These tiny systems are 7 inches wide × 4 inches deep × 1 inch high. Due to their size, they are rather limited in function. Keyboards, for example, are too small to permit touch-typing. With notebooks decreasing in cost and weight, palmtops have been losing market share and popularity.

Docking Ports

Docking ports (also known as docking stations) are specialized cases into which an entire notebook computer can be inserted. This allows the notebook to be connected to desktop I/O devices such as full-sized keyboards, CRT monitors, and network connections. At minimum, a docking station provides an alternating current (AC) power source for the notebook. Docking stations are highly proprietary items designed for use with specific computer models. They are handy for the user who wants to maintain only one computer system and avoid the necessity of transferring information between two systems. With a docking port and a well-equipped notebook computer, it is possible to have the best of both worlds.

It is not necessary to have a docking port to use a portable computer with a full-sized keyboard, pointing device, and monitor. Most portables have standard connectors for these peripherals. However, be aware that you might have to connect the devices before booting up the computer.

Notebook Computers

Advances in integrated circuit (IC) technology allowed the size of computer components to be reduced even further, and, in the early to mid-1980s, the notebook computer was born.

Notebooks are roughly 8.75 inches deep × 11 inches wide × 2.25 inches thick, and designers are working to decrease the size and power consumption of these units even further. The reduction in size comes at a cost, however, and notebooks typically have smaller and less capable displays and keyboards than laptops. A wide variety of specialty items have appeared on the market designed to overcome some of the notebook's shortcomings. Docking ports are one such item.

Laptop Computers

With advancements in battery technology and the advent of functional, large-screen, liquid crystal displays (LCDs), the first truly portable computers, referred to as laptops, were produced in the late 1980s. These units featured integrated AT-compatible computer boards, including I/O (input/output) and video controller functions. Laptops, as mentioned, usually feature a folding LCD display and a built-in keyboard and pointing device. They also use an external power supply and a removable, rechargeable battery. Today's laptops have fairly large (2 GB or more) hard drives, a CD-ROM drive (or DVD drive), and a floppy disk drive (often the latter two are interchangeable plug-ins).

When laptops originally appeared on the market, they were the smallest portable computers made. Today, they are high-end machines that offer features and performance comparable to a desktop system.

Types of Portables

Portable computers are classified according to size and function. Today there are three basic types of portable computers: laptops, notebooks, and subnotebooks.

The first "portable" computers were often called "luggables." The size of a portable sewing machine, they tipped the scales at 30 pounds. Equipped with a small CRT (cathode-ray tube) display, they were actually a traditional PC in a slightly smaller case.

The real change in portable computers came with the advent of the flat-panel display, allowing the portable to take on the now-familiar slim design. Laptop is the term used for the heavier version, usually offering most of the features of a full-fledged PC but with a folding flat-panel display and integrated keyboard. Notebooks are slender devices that often lack the full range of storage as part of the normal configuration. PDAs, a special group of products offering a subset of features including e-mail, schedule tracking, contact records, and limited note taking and Web browsing, are beyond the scope of this chapter.

Portable Computers

Portable computers are a growing part of everyday life, both for users and technicians. you must understand how to deal with minor problems and answer user questions about proper operation and care.

The category of portable computers includes

laptop,
notebook, and
subnotebook (palmtop) computers,


as well as the newest categories,

PDA (personal digital assistant) and
handheld computers.