PDA Hardware
PDAs are essentially very small computers, and as such they require the same type of hardware as a computer: a processor, memory, and interfaces to connect to the outside world. All this has to be designed to consume as little power as possible so that the device's battery doesn't run out.
Processor
The processor is far less important in a mobile device than in a PC. While desktop PCs are frequently marketed with a large number of MHz (or, increasingly, GHz) as their main selling point, it can be very difficult to discover the speed and even the make of the processor inside a PDA or phone.
The reason is that there is no single common hardware or software platform, so it is harder to make comparisons. The Palm and the PocketPC devices offer comparable performance, but the extra complexity of the Windows CE operating system means that the PocketPC demands far more computing power. Even for users who have settled on an operating system, Windows CE alone has been ported to more than ten different types of processor. Each has its own unique characteristics, making it hard to compare them using only one measure. Nevertheless, clock rate can serve as a rough guide to the power of a system.
All PalmOS devices so far use Motorola's DragonBall chip, a variant of the M68000 used in the original Apple Macintosh. The DragonBall runs at only 16 MHz. This would be too slow for Windows CE, which most users agree feels rather sluggish at anything below 100 MHz.
The EPOC system is more modular, so its processor requirements vary depending on which components are installed—Psion's product range alone spans 8 MHz to 133 MHz. The most powerful processor inside PDAs at present is the StrongARM, originally designed by DEC (Digital Equipment Corporation) but now built by Intel. It can run at up to 200 MHz and uses far less electricity than the x86 chips inside PCs.
The predicted boom in mobile computing has led many companies to develop small chips with a low electrical appetite. The most well known is Transmeta, a Silicon Valley startup that counts Linux father Linus Torvalds among its founders, and has several heavyweight backers, including PC giant Gateway. Its Crusoe processors are able to run a variety of operating systems by emulating the x86.
Memory
Memory has a greater impact than processing power on most computer users. Even in the PC domain, nearly every computer would see greater benefit from a memory expansion than from a processor upgrade. Memory is even more crucial for PDAs, as they have no disk drives. A PC can store most of its data on hard disk, and even use part of the drive as virtual memory if its real memory does run low. A PDA has to keep literally everything within memory, including its store of contacts and appointments, every spreadsheet or word processor file, and even programs that the user decides to install.
As with the processor, different types of PDA require different amounts of memory, though in every case, more is obviously better. The Palm can get by with only 4 MB, while Windows CE machines need at least 32 MB. Again as with the processor, EPOC's requirements vary between these two extremes. The memory and processor requirements of each operating system are summarized in Table 10.2.
Like all computers, PDAs have two types of memory.
ROM (Read Only Memory) stores the operating system and any other programs that the manufacturer has preinstalled. This differs from the architecture of a PC, which has only a very basic ROM telling the computer to load (boot) an operating system from a disk drive. The advantage is that a PDA can be used almost immediately after it is switched on, while a PC can take a minute or more to start up. The disadvantage is that upgrading the software is difficult or impossible.
RAM (Random Access Memory) is for everything specific to the user. Most RAM is volatile, meaning it loses all data when switched off. To avoid such a disaster, PDAs and phones are never switched off completely. Though they may look inactive to the user, there is still a tiny current flowing through the memory. Many even contain a small backup battery to keep the memory active while the main battery is being replaced. This often fails to work or has a very short life, so PDA data should always be backed up on a PC.
There are several different types of RAM available, though exactly which kind is installed only really makes a difference with a fast processor and a memory-hungry operating system, such as Windows CE. Three have found their way into phones and PDAs.
DRAM (Dynamic RAM) is the cheapest, and so used in most mobile devices.
EDO (Enhanced Data Output) is more expensive, but offers a speed increase of about 30 percent over DRAM. It is used by some Windows CE handhelds, such as Compaq's Aero.
SDRAM (Synchronous Dynamic RAM) offers a further 50 percent speed increase and is the standard on PCs. It's still rare in PDAs, but has been built into a few, such as Compaq's iPAQ.
| Operating System | Typical Processor Speed | ROM | Minimum RAM |
|---|---|---|---|
| EPOC 16 | 7.7 MHz | 2 MB | 2 MB |
| EPOC 32 | 36 MHz | 6 MB | 6 MB |
| Palm OS 3.x | 16 MHz | 2 MB | 2 MB |
| Windows CE 2.x or 3.x | 133 MHz | 16 MB | 16 MB |
Interfaces
Despite the ideal of a wireless world, mobile devices still require physical interfaces for cables and expansion modules. In particular, most need some way to connect to a computer so that data can be backed up. Many PDAs still don't have a built-in cellular terminal or even a modem, so linking to a computer can also be the only way to install new software, whether from CD-ROM or the Internet.
Most phones still have only one proprietary expansion plug, used to connect it to accessories such as a hands-free kit, or to a computer for wireless data. PDAs tend to offer a greater choice of options. Many have a USB (Universal Serial Bus) port, a small jack on the back that can be used to connect to most computers built after about 1998. Some also have an infrared port, and interfaces for other equipment, such as a standard keyboard or mouse.
Palm pioneered the idea of a sync cradle, which other manufacturers are now copying. This is a small box that can be left connected to a PC, with the device simply dropped into it for automatic updating. Such things should be unnecessary once Bluetooth is ubiquitous, but manufacturers are already finding other uses for them. Well-designed sync cradles act as battery chargers too, providing a permanent home for the Palm when it isn't in the user's pocket.
The latest trend among tablets is for the manufacturer to sell a variety of proprietary plug-in cartridges, which offer extra functions or expansion ports. They say that this keeps the basic specification light, but it also locks customers into that particular manufacturer's equipment. Such a system was first tried by Psion for its original Organizer, released back in 1984. It was abandoned, but resurrected fifteen years later by Handspring and then Compaq. Known as Springboards, Handspring's expansion modules include a modem, a pager, and even a golf game.
There are also two industry-standard expansion systems found in many PDAs and some phones. Both consist of small slots into which the user can insert one or more cards. Each card can be a complete device in itself, such as a hard disk drive or RAM pack, but they usually involve connecting to something else and so have either a wire or an antenna sticking out.
PC cards were developed in 1990 by the PCMCIA (Personal Computer Memory Card International Association), under whose name they were known until 1995. They can be used in almost all notebook computers, some PDAs, and occasionally in other devices, such as digital cameras. As the name suggests, they were originally intended as an easy way to expand a computer's memory, but are now used for all types of interface. The most common PC cards are modems, network interfaces, and interfaces for mobile phones.
All PC cards are the same shape as credit cards and several millimeters thick. There are three different thicknesses, but all use the same kind of interface. The only difference is how much space is needed to accommodate them. Many PDAs do not have room for the thickest, known as Type III, but this is rarely used except by high-capacity hard disk drives.
CF+ cards are a miniaturized version of the PC card. They are slightly thinner and about half the size in other respects (think of a credit card broken in two). CF+ (Compact Flash) slots are found in many PDAs and some cellphones, and are used for much the same applications as its larger ancestor. The first commercially available Bluetooth products were CF+ cards.
It's possible to use a CF+ card in a PC card slot by putting it inside a simple adapter. This allows people to use the same cards in all their mobile devices and makes it easier for manufacturers to support both.
Power Consumption
For laptop computer users, battery life is the single greatest limitation. Despite advances in battery technology, faster processors and extra features such as CD-ROM drives mean that most still need a recharge after two hours or less. Mobile phones and PDAs last longer, but the increased power consumption of high-speed data services and the planned convergence of phones with computers threaten to change this.
Phone manufacturers quote highly exaggerated battery lives, based on how long the phone can remain on standby. Users need to look instead at the length of talk time, unless they intend never to make or receive calls. Most modern phone batteries have several hours' talk time, enough to last for a full calendar day, provided they are not in constant use. Power consumption also depends on signal strength; the further a digital phone is from its base-station, the louder the broadcast must be.
Battery capacities are measured in watt-hours, which means the number of hours for which the battery could supply a power of 1 watt. This is a very small unit by the standards of electricity. A typical light bulb requires 60 watts, so a watt-hour is enough to keep it going for only a minute. In human metabolic terms, it's less than the nutritional energy contained within a can of diet soft drink. Most mobile phone batteries have a capacity of less than 10 watt-hours, barely enough to heat the water for a lukewarm cup of espresso.
Table 10.3 shows the typical battery capacity needed for some applications. It is only a rough guide. Different brands of battery have different capacities, and many are available in several sizes. Some phone manufacturers give users a choice: a slimline battery that has to be recharged frequently or a large bulging one that can last for many days. But in every case, higher capacities mean a bulkier and heavier battery.
Because battery life is so important, mobile devices are typically very energy-efficient. Though this may seem to be a good thing from a cost or environmental point of view, the amounts of energy concerned are too small to be significant. It may be more important when considering the health effects of mobile phones, as the human body could be sensitive to smaller changes.
A typical phone operates at a power of less than 1 watt, while a microwave oven uses 650 watts or more. This means that it would take at least 650 mobile phones to emit as much radiation as a microwave oven, prompting industry groups to suggest that phones are relatively safe. On the other side of the debate, health advocates warn that many people talk on their mobile phones for at least 650 times as long as a microwave oven takes to cook a piece of meat. However, the effects of heating are not cumulative over long periods of time—the brain has time to cool down in between doses of radiation.
| Device | Battery Capacity | Lifetime | Usual Type |
|---|---|---|---|
| Electric Car | 1000 watt-hours | 1 hour | Lead-Acid |
| Laptop PC | 50 watt-hours | 2 hours | LiON |
| Mobile Phone | 10 watt-hours | 10 hours talk | NiMH |
| PDA (AA battery) | 2 watt-hours | 20 hours | NiCAD or Alkaline |
| Digital watch | 0.1 watt-hours | 2 years | Zinc Carbon |
normal: Why Are Microwaves DangerousAs explained in Chapter 2, "Radio Spectrum," microwave frequencies are too low to ionize atoms, so they can't directly cause cancer in the same way as ultraviolet or nuclear radiation. But they do produce a heating effect, and unlike other types of heat, we may not feel microwaves until it is too late. This is how they were first discovered: in 1946, a researcher noticed that a chocolate bar in his pocket had melted during an experiment, even though he hadn't been aware of any heat. Microwaves are not alone in their heating effects. All types of electromagnetic waves carry energy, and so can increase the temperature of anything or anyone they strike. The type of electromagnetic wave we are most familiar with is infrared radiation, which is given off by all hot objects. A radiator works by emitting infrared radiation, which we can feel. As the temperature of the hot object increases, the atoms within it vibrate faster, so the frequency of radiation also increases. "Red hot" objects emit red light (the lowest frequency in the visible band), and "white hot" objects (such as lightbulbs) radiate all colors. If we stand next to a radiator or underneath a spotlight, we feel hot. This is because the radiation is absorbed mainly by our skin, which contains lots of nerve endings. Unfortunately, the same isn't necessarily true for microwave radiation. It is so low in frequency that much of it passes straight through our skin. The microwaves are instead absorbed by internal organs and bones, which don't contain many nerve endings. This effect is used by some medical equipment to produce heat deep inside the body without hurting the skin. It can also cause health problems. A microwave transmitter can burn us just as much as a lightbulb or a radiator can, but since we don't feel the heat, we aren't aware of damage being done. A mobile phone could cook our brains or boil our blood before we realize it. Other radio waves use even lower frequencies than microwaves, so in theory these could have similar effects. However, their frequencies are so low that they carry very little energy and often pass straight through the human body. Microwaves are close to the resonant frequency of water, meaning that they cause water molecules to vibrate rapidly. Microwaves may also have some nonthermal effects, meaning they could produce damage in other ways. For example, all radio receivers can also act as transmitters, and vice versa. Just as objects are heated by radiation, hot objects radiate. Anything that has been exposed to microwaves may emit them for a short time afterwards. This is why some people like to leave food to wait for a minute or two after it has come out of a microwave oven. More controversially, some scientists have suggested that radio waves are actually used within the brain, and that some effects could be due to interference. It's known that powerful magnets can affect the brain, producing an effect similar to hallucinogenic drugs, but the fields associated with microwave radiation are thought to be too weak for this. Extensive research has been carried out on the effects of low-power fields, mainly related to the safety of electrical wires, and they have been shown to cause no increase in cancer or any other illness. |
Batteries
Almost all batteries built into mobile equipment are known as secondary power cells, which means that they can be recharged. There are four main types.
Lead-Acid batteries were used in some very early mobile phones, but are now reserved mainly for vehicles and industrial applications. They are relatively cheap and can be recharged an indefinite number of times, but the ingredients are quite dangerous.
NiCAD (Nickel Cadmium) batteries are the cheapest type of rechargeable battery. They can be recharged up to 1,000 times, but need to be completely discharged each time. If not, they can suffer from a memory effect. At its most extreme, this memory effect means that devices can only access the electricity put into the battery during its last charge, not any left from previous charges.NiCAD batteries used to be very common in all kinds of devices, but thanks to the memory effect are now rarely fitted as standard in computing or communications equipment. Their main use is as a replacement for disposable batteries, and they are usually the type supplied with home battery chargers. Environmentalists have criticized NiCAD batteries because they contain the pollutant cadmium, though they are still considered far more environmentally friendly, and cheaper, than disposables.
NiMH (Nickel Metal Hydride) batteries are slightly more expensive than NiCAD batteries, but have up to 25 percent more capacity for the same size and weight. Their main advantage is that they don't suffer from the memory effect. A user can top up the battery whenever convenient, even if it has just been charged a few minutes ago. They are found in most mobile phones and some laptop PCs.
LiON (Lithium Ion) batteries also resist the memory effect and provide higher capacities than other types. They are also more expensive, so many manufacturers of phones and laptops give their customers a choice: if long battery life is important, they can pay about $50 extra to have a LiON battery.
Smart Batteries can be based on either LiON or NiMH technology and include a built-in power meter. This is used by power management features in mobile devices and by chargers so that they know when to stop.
Alkaline and Zinc-Carbon are ordinary nonrechargeable batteries, known in the jargon as primary powercells. Of the two, alkalines offer the highest capacity, and are more expensive. The most common are the AA size, used by many Palm and Psion PDAs.
Nonrechargeable batteries are not normally used in mobile phones, though kits are available that enable them to act as an emergency power source. The theory is that if a user is stranded away from a power source, she will be able to buy a relatively cheap disposable battery that gives the phone a few minutes of talk time. Another emergency power option is the Zinc-Air booster, a small device kept in a sealed foil pack that reacts with oxygen to provide a full power charge.