In this section, we will describe the I/O devices, I/O interface, and modes of transfer.
（1）Keyboards.
Computer keyboards were originally designed to imitate electric typewrites so that typists could learn to use computers more easily. The demands of computer technology, however, have led to keys and keyboard layouts never before seen on a typewriter. While a typewriter has only about 50 keys, a computer keyboard may have 100 or more. A computer's keys are generally divided into four clusters: alphanumeric keys, function keys, cursor keys, and the numeric keypad. Alphanumeric keys include letters, numbers, and punctuation marks. They are arranged much like the keys on a typewriter. Function keys are labeled F1, F2, and so on up to F12 or F15. They can be used for giving common commands such as “Print” or “Quit program”. The precise purpose of any function key varies from one program to another. Cursor keys are used to move the cursor around on the screen. The cursor is the little blinking symbol that indicates where things will happen next on the screen. When you are typing, the cursor always blinks just to the right of the last character you typed. Cursor keys include the arrow keys for moving up, down, left, and right, as well as the PageDown, PageUp, Home, and End keys. The numeric keypad includes the mathematical keys found on a standard calculator.
（2）Mouse.
Mice are popular because it is easier to point than to type, and because the arrow keys don't work very well for drawing pictures or moving things on the screen. A mouse consists of a ball mounted under a plastic housing with one or more buttons on top. As you move the mouse around the tabletop, sensors inside register the rolling of the ball and move the cursor around the screen to match. There are three basic ways of giving commands with the mouse. First, you can click the button to identify something—perhaps to indicate which part of a drawing you want to change. Second, you can drag the mouse; that is, you can hold the button down while you move the mouse. Dragging can be used to move a drawing across the screen. The third way to give a command is to double-click the mouse's button by pressing it twice within about a half second. Double-clicking is used to select things on the screen.
The simplest pointing tool of all, of course, is the finger. In fact, touch screens are widely used in department—store advertising displays, information kiosks, lottery game machines, and other places where users are not expected to have much familiarity with computers. On these machines you simply touch the part of the display screen you want to select, just as you might push a vending machine's button. Depending on the sensing method used by the touch screen, your finger might interrupt a network of infrared rays protected across the screen's surface. This would tell the computer where you pointed.
（3）Monitor.
A monitor, or display screen, provides a convenient but temporary way to view information. The earliest computer monitors were simply converted television sets. While ordinary TVs are still used for some video games, most computer programs today demand higher-quality monitors. The quest for better monitors has taken two paths: the improvement of TV-like screens and the development of flat screens.
（4）Printers.
Different kinds of computer printers use surprisingly different technologies. Some printers squirt ink, some apply heat to sensitive paper, others hammer inked ribbons, and still others create images with lasers. Laser printers work by reflecting a laser beam from a rapidly rotating octagonal mirror onto a light-sensitive roller. Ink-jet printers work by squirting tiny droplets of liquid ink at the paper. Dot-matrix printer features a movable print head containing a row of tiny pins. The pins push an inked ribbon against the paper, producing a matrix (or pattern) of dots. As the print head moves back and forth across the page, the dots can form either letters or graphics.
（5）Modem.
A modem, short for modulator-demodulator, is used for communicating between computers. The modem converts a computer's electronic impulses to a form that can be transmitted over a telephone line. When the signal reaches the destination computer, another modem reconverts the signal to computer understandable form. Some modems are book-sized boxes that plug into the back of a computer; others fit inside the computer's housing.
Input-output interface provides a method for transferring information between internal storage and external I/O devices. Peripherals connected to a computer need special comm-
unication links for interfacing them with the central processing unit. The purpose of the communication link is to resolve the differences that exist between the central computer and each peripheral. The major differences are:
· Peripheral are electromechanical and electromagnetic devices and their manner of operation is different from the operation of the CPU and memory, which are electronic devices. Therefore, a conversion of signa1 values may be required.
· The data transfer rate of peripherals is usually slower than the transfer rate of the CPU, and consequently, a synchronization mechanism may be needed.
· Data codes and formats in peripherals differ from the word format in the CPU and memory.
· The operating modes of peripherals are different from each other and each must be controlled so as not to disturb the operation of other peripherals connected to the CPU.
To resolve these differences, computer systems include special hardware components between the CPU and peripherals to supervise and synchronize all input and output transfers. These components are called interface units because they interface between the processor bus and the peripheral device. In addition, each device may have its own controller that supervises the operations of the particular mechanism in the peripheral. Each peripheral device has associated with an interface unit. Each interface decodes the address and control received from the I/O bus, interprets them for the peripheral, and provides signals for the peripheral controller. It also synchronizes the data f1ow and supervises the transfer between peripheral and processor.
Binary information received from an external device is usually stored in memory for later processing. Information transferred from the central computer into an external device originates in the memory unit. The CPU merely executes the I/O instructions and may accept the data temporarily, but the ultimate source or destination is the memory unit. Data transfer between the central computer and I/O devices may be handled in a variety of modes. Some modes use the CPU as an intermediate path; the others transfer the data directly to and from the memory unit. Data transfer to and from peripherals may be handled in one of three possible modes:
· Programmed I/O.
· Interrupts.
· Direct memory access (DMA).
（1）Programmed I/O.
Programmed I/O operations are the result of I/O instructions written in the computer program. Each data item transfer is initiated by an instruction in the program. Usually, the transfer is to and from a CPU register and peripheral. Other instructions are needed to transfer the data to and from CPU and memory. Transferring data under program control requires constant monitoring of the peripheral by the CPU. Once a data transfer is initiated, the CPU is required to monitor the interface to see when a transfer can again be made, It is up to the programmed instructions executed in the CPU to keep close tabs on everything that is taking place in the interface unit and the I/O device.
In the programmed I/O method, the CPU stays in a program loop until the I/O unit indicates that it is ready for data transfer. This is a time-consuming process since it keeps the processor busy needlessly. It can be avoided by using an interrupt facility and special commands to inform the interface to issue an interrupt request signal when the data are available from the device. In the meantime the CPU can proceed to execute another program. The interface meanwhile keeps monitoring the device. When the interface determines that the device is ready for data transfer, it generates an interrupt request to the computer. Upon detecting the external interrupt signal, the CPU momentarily stops the task it is processing, branches to a service program to process the I/O transfer, and then returns to the task it was originally performing.
（2）Interrupts.
An alternative to the CPU constantly monitoring the flag is to let the interface inform the computer when it is ready to transfer data. This mode of transfer uses the interrupt facility. While the CPU is running a program, it does not check the flag. However, when the flag is set, the computer is momentarily interrupted from proceeding with the current program and is informed of the fact that the flag has been set. The CPU deviates from what it is doing to take care of the input or output transfer. After the transfer is completed, the computer returns to the previous program to continue what it was doing before the interrupt.
The CPU responds to the interrupt signal by storing the return address from the program counter into a memory stack and then controls branches to a service routine that processes the required I/O transfer. After the transfer is completed, the way that the processor chooses the branch address of the service routine varies from one unit to another. In principle, there are two methods for accomplishing this. One is called vectored interrupt and the other, nonvectored interrupt. In a nonvectored interrupt, the branch address is assigned to a fixed location in memory. In a vectored interrupt, the source that interrupts supplies the branch information to the computer. This information is called the interrupt vector. In some computers the interrupt vector is an address that points to a location in memory where the beginning address of the I/O service routine is stored.
（3）Direct memory access (DMA).
Another aspect of computer system performance that can be improved is the transfer of data between memory and I/O devices. This is a common operation in computer systems. Loading programs or data files from disk into memory, saving files on disk, and accessing virtual memory pages on my secondary storage medium all fall into this category of operations.
Consider a typical system consisting of a CPU, memory, and one or more input/output devices. Assume one of the I/O devices is a disk drive and that the computer must load a program from this drive into memory. The CPU would read the first byte of the program and then write that byte to memory. Then it would do the same for the second byte and each succeeding byte, until it had loaded the entire program into memory.
This is, at best, inefficient. Loading data into, and then writing data out of, the CPU significantly slows down the transfer. The CPU does not modify the data at al1, so it only serves as an additional stop for data on the way to its final destination. The process would be much quicker if we could bypass the CPU and transfer data directly from the I/O device to memory. Direct Memory Access, or DMA does exactly that.
A DMA controller implements direct memory access in a computer system. It connects directly to the I/O device at one end and to the system buses at the other end. It also interacts with the CPU, both via the system buses and two new direct connections.
To transfer data from an I/O device to memory, the DMA controller first sends a bus request to the CPU by setting BR to1. When it is ready to grant this request, the CPU sets its bus grant signal, BG, to 1. The CPU also tri-states its address, data, and control lines, thus truly granting control of the system buses to the DMA controller. The CPU will continue to tri-state its outputs as long as BR is asserted.
Now that the DMA controller has control of the system buses, it can perform the desired data transfers. To load data from an I/O device into memory, it asserts the appropriate I/O control signals and loads data from the I/O device into its internal DMA data register. Next, it writes this data to memory. To do this, it outputs the memory address onto the system's address bus and the data onto the data bus. The DMA controller also asserts the appropriate signals on the system's control bus to cause memory to read the data. DMA coddler then writes the second data value to the following memory location, continuing until it has transferred the entire block of data.
To understand how the DMA controller performs this transfer, we must examine its internal architecture. The DMA controller includes several registers. The DMA address register contains the memory address to be used in the data transfer. The CPU treats this register as one or more output ports. The DMA count register, sometimes called the word count register, contains the number of bytes of data to be transferred. Like the DMA address register, it is also treated as an output port by the CPU. The DMA control register accepts commands from the CPU. Most DMA controllers also have a status register. This register supplies information to the CPU, which accesses it as an input port. DMA controllers also usually include circuitry to abort the transfer if the I/O device is not ready in some predetermined amount of time. This is called timeout.
|
I/O subsystem |
输入/输出子系统 |
PCI bus |
PCI总线 |
|
DMA |
直接存储器存取 |
alphanumeric keys |
字母数字键 |
|
address bus |
地址总线 |
numeric keypad |
数字键 |
|
data bus |
数据总线 |
infrared rays |
红外线 |
|
control bus |
控制总线 |
dot-matrix printer |
点阵式打印机 |
|
local bus |
局部总线 |
|
|
（1）DMA（直接存储器存取）。它是一种完全由硬件执行I/O变换的工作方式。在这种方式中，DMA控制器从CPU中完全接管对总线的控制，数据交换不经过CPU，而直接在内存储器和I/O设备之间进行。
（2）Local bus（局部总线）。一种PC总线结构，为提高系统性能而设计，使某些扩展板可直接与微处理器通信，而不必经过通常使用的系统总线。
（3）PCI bus（PCI总线）。它是由Intel 提出的一种局部总线系统的规范，该规范允许在计算机上安装至多10个PCI兼容的扩展卡。PCI总线系统需要在某个PCI兼容插槽中安装一块PCI控制卡。根据实现情况的不同，PCI控制卡可以按每次32位或64位的速度与系统CPU进行数据交换，而且通过使用总线控制技术，PCI控制卡还允许智能化的PCI兼容适配卡与CPU并发地执行任务。PCI规范还考虑到了多路复用的情况。
1. Fill in the blanks with appropriate words or phrases.
（1）I/O control can be classified into two broad categories: .
（2）I/O system needs a buffer when of source and destination differ.
（3）The tasks of I/O system can be performed by .
（4）Programmed I/O is also known as .
（5）Memory-Mapped I/O maps the device connections to in memory address space.
（6）If there is only one processor in a computer system, the processor efficiency should be .
（7）Memory coherency is one of problems with using .
（8）In Memory-Mapped I/O any instruction of referencing memory can address .
（9）When a device is ready to transfer data, it sends an to the processor.
（10）A major function of the I/O system is to match their latencies and bandwidth to that of .
A．hardware and software F．bandwidths and latencies
B．lower G．bits
C．programmed I/O and coprocessor I/O H．interrupt signal
D．the memory system I．coprocessor I/O
E．memory-mapped I/O locations J．direct I/O
2. Match the following terms to the appropriate definition.
（1） interactive inputs.
（2） nonimpact printers.
（3） source data automation.
（4） display outputs.
（5） sensor input.
（6） impact printer.
（7） liquid-crystal display (LCD).
（8） digitizer.
（9） speech-recognition devices.
（10） optical scanner.
A．CRT is basically a television tube adapted to present text, data, or images generated by computers.
B．A number of methods have been developed to increase speed, accuracy, and reliability of input.
C．Screen-dependent inputs.
D．A device reads printed material so that it can be put in computer-readable form.
E．Dot-matrix printer.
F．A device accepts voice information through a microphone.
G．Ink-jet printer and laser printer.
H．Home computer links to thermometer, light detector and motion detector.
I．A tool of technical applications especially used for engineering.
J．A common electronic imaging technique used in flat-panel displays.
JUST WHAT IS THE UNIVERSAL SERIAL BUS?
The Universal Serial Bus is one of the fastest-growing and most widely accepted expansions to the personal computer in recent memory. It is impossible to buy an Intel-based PC (which makes up 94 percent of the personal-computer market)without a Universal Serial Port Bus. This is not to say that the USB is limited to the PC world, not by any stretch. Every computer, hardware manufacturer is now acting to implement the Universal Serial Bus on its own platform.
Why the sudden interest in something as seemingly trivial as an serial port? The answer is that the Universal Serial Bus is much more than a serial port—it's a serial bus. This means that a single port on the back of your computer can be the window (no pun intended) into a myriad of devices. Devices can be daisy-chained together. Groups of devices can be separated by concentration hardware called a hub. When you think of the Universal Serial Bus, it's best to think of it as a “network” of device, much as you would think of the Ethernet network.
Chaining a bunch of devices together might not seem like such a good thing at first glance. In fact, it might seem like a downright bad idea for a lot of devices to share what little bit of bandwidth serial devices have traditionally had to work with. After all, there is barely enough bandwidth on an RS-232 port to get a decent connection to a printer. There certainly isn't enough to talk to a digital camera to download images.
The answer lies in providing a fast bus. We have to be careful with our terminology, though, because the Universal Serial Bus is considered in the computer industry to be a “mid- and low- speed” bus.
The Universal Serial Bus operates at over 10 million bits per second, this is the speed of the computer network in most businesses.
The Universal Serial Bus is not considered “fast” when compared to things such as the Fiber Channel serial bus, which clocks in at about 300million bits per second, or to upcoming bus technologies such as the IEEE 1394 “Firewire” bus to control audio and video sources that are “broadcast quality”. So we will accept that the USB is a “mid-speed” bus and move on.
The Universal Serial Bus was designed with the thought of providing pure digital audio, video, and telecommunications to the modern computer user. The speed of the bus is more than sufficient to support these types of devices.
A big problem with personal computers has always been connecting to the peripherals that you want to use. Everything always seems to need its own adapter card plugged into the bus. There are video cards for high-resolution video. There are game cards to drive your joysticks. There are sound cards to drive speakers and there are video-input cards to bring video into the computer. The list goes on and on.
Computers are shrinking. Every year there are fewer slots for adapter cards. The goal of the personal computer industry truly is to make the computer as ubiquitous and unobtrusive as possible. At the same time, the computer now contains sufficient technology and raw “horsepower” to run the types of applications and drive the types of tasks that are requiring precision digital input and bandwidth intensive peripherals. Video conferencing on personal computers is today a reality. Surround sound stereo from your persona1 computer is a standard function.
The computers industry is striving to enclose a technology that is expanding to the point that mid-and high-speed digital peripheral devices are required into an ever shrinking footprint. This is where the Universal Serial Bus comes into play. Just put all of the input and output to peripherals outside “the box” and don't use any slots. Put the intelligence into the devices, rather than into the computer.
Peripherals designers are now freed up to implement solutions that are in “one piece” they don 't have to split the functionality of a peripheral between a device and an interface card. This is a win for them. As this happens, the internal bus on your computer ceases to be saturated with traffic and information flowing between these interface cards. This is a win for you; you'll find that you achieve better overall system performance with this type of configuration.
Speaker designers are incorporating the functions previously performed by your sound card directly into the speaker. Video-input folks are building video digitizers to plug into the Universal Serial Bus. Even monitor manufacturers are putting Universal Serial Bus interfaces into the backs of their monitors, making the video card obsolete. There are digital joysticks that offer super high resolution.
The Personal Printers
Cost-conscious families, students and home-office users often buy sub-$100 inkjets as an economical way to get basic printing capabilities. These super cheap machines traditionally sacrifice a lot of features to keep their prices low, but the three models in this text offered at least a few surprises: some impressive output; print speeds that were, in certain cases, astonishing; and useful features from novice-friendly setup tutorials to sophisticated photo-enhancement controls. Just keep an eye out for hidden long-tem tradeoffs, such as having to buy an interface cable (none of the machines we tested came with one), shelling out for pricey inks, or fiddling with flimsy paper trays that won't stand up to rough family use.
The Epson Stylus C60's trade-offs are tolerable ones. The inkjet prints text quickly but not perfectly, and it produces breathtaking photos—but very slowly. Add to this tricky balance some very novice-friendly documentation and inexpensive inks, however, and the C60 becomes a solid choice for home users or students, as well as for digital shutterbugs on a budget.
New users will appreciate the $79 Epson Stylus C60's user-friendly approach. The printer comes with a big colorful Start Here card that walks you through connecting the printer, installing the ink and the paper and setting up the drivers. A Printer Basics booklet gives you more detailed advice on troubleshooting and even packing the printer for transport. The included CD-ROM has a more detailed Reference Guide, Epson Print Show movies (animated movies that demonstrate basic printing and usage) and drivers (for parallel connection: Windows 95, 98, Me, 2000 and XP; for USB: Windows 98, Me, 2000 and XP plus Mac OS 8.5.1 to 9.1; OS X drivers are available online). You also get Epson Film Factory Lite, a program that lets you collect, edit and store all kinds of digital images. The only thing not included is a USB or parallel cable, so you may need to buy one.
The Stylus C60's compact design should fit configurally on most desktops. The input tray, which holds 100 sheets of plain paper, is vertically attached to the top back of the printer, adding about one foot in height. The output tray extends from the front base and adds about six inches in depth. Still, the printer supports various paper types including envelopes, photo paper, cards, transparencies, and stickers.
The Stylus C60 drivers are sophisticated but still approachable, even for new users. In addition to basic functions such as Paper Type and Orientation, a plethora of preset and customizable image, color-management settings, such as Photo Enhance, let you adjust the printer's palette for people, nature images and more.
But these perks would be nothing without fast, good-quality output, and the C60 meets you at least halfway. In our labs' test, the Stylus C60 printed text at 5.9 pages per minute—faster than many more-expensive inkjets. Letters looked good on both plain paper and Epson's Photo Quality Inkjet paper. We noticed some jaggedness and fine horizontal striping, but overall, the type was dense and well saturated. Photo printing was quite a bit slower, at 62 minutes per 8×10 photo, but the results were worth the wait; skin tones on our test photo looked smooth and natural, and colors were rich and accurately rendered. Graphics on plain paper had good color matching and smooth shading. On Epson's inkjet paper, colors were accurate—if a little bright—and photo elements looked smooth.
Many inkjets look cheap until you have to buy replacement inks—but not the Stylus C60. Prints will cost you a reasonable 6 cents per page of text and 26 cents per color page.
Epson backs the Stylus C60 with a typical service and support plan. You can extend the one-year warranty to two years for $14.95; a three-year plan costs $24.95. Free phone support is available for the life of the product; Monday through Friday from 6 a.m. to 8 p.m. and Saturday from 7 a.m. to 4 p.m. PT. The Epson Web site offers useful resources such as the latest drivers (including one for Mac OS X), FAQs, and manuals.
No sub-$100 printer is going to be perfect, but the Epson Stylus C60 balances its good and not-so-good points skillfully. Students will like the inkjet's fast-printing, decent-looking text; amateur photographers will love the beautiful prints, even though they emerge slowly; and pretty much anyone will appreciate the affordable price.
（1）Printer type.
Three technologies dominate personal printers: inkjet, laser, and to a lesser extent, LED (light-emitting diode). Using replaceable cartridges that spray fine droplets of ink, personal inkjet printers cost the least, print slowly, and often produce impressive color output. Laser and LED printers use a process similar to that of a photocopier, where a light-sensitive drum rolls charged black toner particles onto paper—producing crisp, fast printouts. Almost all workgroup models employ laser or LED technology due to higher print speeds and easier maintenance.
（2）Output type.
Want to print lots of monochrome pages? Buy a laser or LED printer for its speed and low cost of consumables. Need affordable color? Get an inkjet printer. Photo-quality inkjets generally produce the best homemade color photos, but be forewarned that they usually print slower than your average inkjets (which are slow to begin with). Don't buy an inkjet just to save money: the price up front will be lower than that of a laser, but the cost of an inkjet's color cartridges and coated paper add up quickly. Businesses that need color output quick and in high volume tend to choose color lasers or LEDs, which are reasonably fast and quite expensive. Graphics pros should also explore special-purpose color printers, which employ such alternative technologies as solid ink, dye sublimation, thermal auto chrome, thermal wax, and more.
（3）Maximum resolution.
Personal laser printers produce 600 dots per inch (dpi) —sufficient resolution to create crisp monochrome output. Some expensive workgroup lasers deliver 1200 dpi or even 2400 dpi inkjet printers typically claim output resolutions of 1200 dpi or 2400 dpi, but the sharpness isn't comparable to that of lasers because inkjet print heads lay down tiny splotches of liquid ink line by line, a far less precise process. Generally, you should ignore inkjet dpi claims and compare actual printouts (or the image quality results in our reviews) when possible.
（4）Installed memory.
Personal printers typically need little memory. Inkjets require a tiny amount; just enough to hold the row of dots being printed and maybe a little more. Laser and LED printers are page printers, which means that they must render an entire page in memory before printing. However some personal models are host-based printers and cut costs by using the processing power and memory of your PC to manage print jobs. Top-of-the-line workgroup printers that plug directly into a local network may hold multiple pages, letterhead graphics, forms, special fonts, and more, so expect between 32 MB and 128 MB of memory out of the box (expandable to 256 MB or 384 MB).
（5）Maximum speed.
Measured in pages per minute (ppm), this specification is always exaggerated. Laser printers generally print text pages only slightly slower than the manufacturers' claims. But the claims for inkjet are typically at low-quality settings using very simple text pages—in other words, a speed you'll never see in real life. Reality check: Printing a single 8×10 color photo on an inkjet may take anywhere from 2 to 15 minutes.
（6）Monthly duty cycle.
A manufacturer specification that suggests the maximum number of pages a printer should handle per month. This is primarily a concern for small-office and workgroup printers, not personal printers. Here's a rule of thumb often used by IT departments: To avoid breakdowns, buy a printer with a monthly duty cycle approximately four times the number of pages you think that you'll actually print per month.
（7）Interface.
Almost all personal printers now come with a Universal Serial Bus (USB) port, which is much faster than the old-fashioned parallel port. Only antiquated computers lack USB support. For larger workgroups, you’ll want a printer that hooks directly to the network via Ethernet port.
（8）OS support.
A bigger issue than you might imagine. A few printers lack Mac support entirely, and a number of manufacturers take their time before offering drivers that are fully compatible with the latest version of Windows. Companies that shy away from producing new drivers in a timely fashion may arbitrarily shorten the useful life of your printer.
（9）Warranty and support.
Printers typically come with warranties of one or, at most, two years. Some manufacturers also offer extra-cost, extended warranties for workgroup models.
The pda
If you're wondering why the Maestro PDA-1032 looks a lot like Toshiba’s Pocket PC e570, it's because this PDA is basically Toshiba's device—minus 32 MB of RAM—with Audiovox's name slapped on it. The Toshiba is one of our favorite Pocket PCs, so it's not surprising that we're also quite fond of this one. Its slim size and dual card slots make it very appealing, but because it has less RAM, it's not the right choice for everyone.
The $499 Maestro looks identical to Toshiba's $570 e570 except for the logo. At 4.9×3.0×0.7 inches, it's slightly smaller than Compaq's iPaq H3760. However, you’ll find both CompactFlash type II and Secure Digital (SD) card slots crammed into that compact case. That means that you can add a big SD card for storing media files and applications as well as plug an Ethernet, a Wi-Fi, or a Bluetooth card into the CompactFlash slot to keep your device connected.
Inside, the Maestro has the same 206 MHz Intel Strong ARM processor and 32 MB of ROM as other Pocket PC 2002 devices we've tested. Since MultiMedia Memory cards (MMC) also work in the SD slot, we added a 32 MB MMC (purchased online for $24) to get a PDA with essentially the same abilities as the e570. We tried it with music, Word documents, Excel files, and a number of games, finding no significant difference in the user experience, whether we put the files on the storage card or in the system RAM. However, with the graphically intense game Chopper Alley, loading times were noticeably longer when using the storage card than when using the system memory.
No matter what sort of applications you run, they look good on the Maestro's 3.5-inch reflective LCD. The screen is 0.25 inches smaller than that of the iPaq, but that helps keep size and weight down. We found the 320×240-pixel, 65000-color display to be bright, sharp, and readable in all lighting conditions. Below the screen are the de rigueur four application buttons and a small but exceptionally finger-friendly directional pad. A Record button for taking voice notes rests on the Maestro's side, but it's well recessed so that you don't start recording accidentally. The whole package feels nice and solid in your hand. Fashion-conscious souls can opt for replacement rubber grips, which are available in assorted colors. To protect the Maestro, Audiovox includes only a faux-leather case.
The Maestro is better connected than the Toshiba. Even though it comes with the same USB cradle to sync with your PC, it also has a cable and a preinstalled modem driver to link it to the Audiovox CDM-9100. You can then surf the Internet wirelessly via the phone. Sprint and Verizon also sell a $649 package that includes both the Maestro and the aforementioned phone. However, be forewarned: The cable is awkward, and the connection is pretty slow (14.4Kbps maximum).
A built-in lithium-polymer battery powers the Maestro. While rated for eight hours of use, the battery ran for just more than two hours in our tests. That's about the same as other Pocket PCs that we've tested.
Audiovox backs the Maestro with a one-year Warranty. We weren't able to find much helpful support information for the PDA on the company's Web site, but you can check Toshiba's site if you run into trouble. If you need to speak to real person, you can call Audiovox at 800/229-1235 Monday through Friday during East Coast business hours. But if you're really concerned about the quality of the support, we had a better experience dealing with Toshiba on the phone. We waited for a shorter length of time, and the person who answered was capable of helping us through our simple problem.
Many users will find the $499 Maestro to be an excellent value, especially since you can pick up a 128 MB SD card for less than $70. Such a purchase will allow you to store lots of music, games, and business files, all at the same price you'd pay for the e570 alone. However, if you plan to run very sophisticated applications on your Pocket PC, having more system RAM will be advantageous.
· Backlight display: A source of light behind the LCD display that makes it easier to read.
· Batteries rechargeable: Certain types of batteries can be recharged using the docking cradle or directly with an AC adapter.
· Battery amount: The physical number of batteries required to operate the unit.
· Battery type: Some handheld PCs use standard alkaline batteries; others have built-in rechargeable batteries. The most common type of rechargeable battery is lithium-ion which is ideal for portable devices because of its lightness and high energy density. Lithium-polymer is a newer battery type that theoretically delivers longer battery life ounce-for-ounce.
· Computer interface: All handheld PCs offer one of two types of interfaces for making a physical connection with a host PC to synchronize data and upload programs: serial or USB (Universal Serial Bus). An older standard, the serial interface transmits only 1 bit at a time. Nearly all PCs with the exception of some of the newest “legacy-free” models, include serial ports. USB is a more recent standard that is significantly faster. It supports data transfer rates of 12 Mbps (12 million bits per second). A single USB port can be used to sting together multiple devices, and USB is generally plug-and-play making installation easier.
· Display: Short for display screen. Handheld PCs use a thin display screen known as an LCD (Liquid Crystal Display). There are several types of LCD displays.
· Display size (diagonal): Refers to the length of display in inches form one comer to the opposite comer.
· Dimensions: This refers to the physical dimensions of the unit—the height, width, and depth as held in your hand—measured in inches.
· Docking cradle included: Some handheld PCs include a cradle into which you can insert the device to synchronize data and upload programs from a host PC and/or recharge the batteries. Less-costly models only include a data cable, not a full cradle.
· Expansion slots: Refers to the physical slots found on some handheld PCs that can accept certain types of media such as Compact Flash, MMC (MultiMedia Card), Sony's MemoryStick, and Handspring's Springboard modules. Depending on the type, these cards may be used for additional storage, peripherals such as modems and network adapters, or third-party programs such as games.
· Flash memory (ROM): In contrast to RAM, ROM (acronym for read-only memory) is a type of memory on which data has been prerecorded. Generally, once data has been written onto a ROM chip, it cannot be removed and can only be read. Unlike main memory (RAM), ROM is non-volatile, meaning it retains its contents even when the computer is turned off. All handheld PCs include a small amount of ROM where critical programs such as the operating system are stored. The amount of ROM on a handheld PC is also measured in megabytes—typically anywhere from 2MB to 16 MB depending on the operating system. Some handheld PCs, but not all, have upgradeable ROM, which means that you can upgrade to new versions of the operating system as they become available.
· Handwriting recognition software: An application that understands your handwriting and transforms it into digital data. Different handheld PCs take different approaches. Palm-based organizers use Graffiti, a shorthand alphabet that is relatively easy to use but takes time to learn. Other handheld PCs attempt to recognize your natural handwriting.
· Host PC platform: The host PC is the desktop or notebook PC that you attach to your handheld PC via a cable cradle, or infrared to synchronize data and upload programs. The term platform refers to the operating system on the host PC with which the handheld PC is compatible.
· Infrared port: Often referred to as IrDA after the organization that runs the specification (Infrared Data Association), infrared is a standard for transmitting data via infrared light waves. Most handheld PCs come with an infrared port that can be used to synchronize data with a host PC or to exchange data such as electronic business cards with other handheld PC. IrDA ports support roughly the same transmission rates as traditional parallel ports, and the two devices must be with in a few feet of each other and there must be a clear line of sight between them.
· Internal memory (RAM): All PCs including handhelds have internal storage in the form of computer chips. The main memory is known as RAM, an abbreviation for RAM (random-access memory). The term RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. Known as volatile memory, RAM requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost. RAM is measured in megabytes and the amount of handheld PCs varies widely (currently anywhere from 2MB to 32MB) depending on the operating system and applications.
· LCD type: There are two basic types of color LCD displays. Thin film transistor (TFT) or active-matrix displays produce color images that are as sharp as traditional CRT displays (your desktop PCs monitor), but the technology is expensive. Passive matrix is less expensive, but images are not as crisp and bright. Newer passive matrix technologies such CSTN and DSTN are closing the gap with active matrix displays.
· MP3 player: It derives from the file extension for audio files that use MPEG, audio layer 3 compression. Since this is the most common format, it has become shorthand for distal audio. Some handheld PCs, specifically Pocket PC, include a player program that can play both MP3 and Windows Media audio files.
· Number of colors displayed: Technically, the color display capability of a display is measured by the number of bits used to represent each dot on the screen. To simplify things, this can be converted into the total number of colors that can be reproduced: a 1-bit image is monochrome; an 8-bit image supports 256 colors or grayscales; a 12-bit image supports 4096 colors, and a 16-bit image has 65536. True color (24- or 32-bit graphics) is currently not supported by any of the major handheld PCs.
· Number of gay shades displayed: The terms monochrome and gray-scale are now used interchangeably to refer to screen displays that can only display shades of gray, not color. Most Palm-based organizers are gray scale and typically display anywhere from 4 to16 shades of gray depending on the model.
· Operating system: The most important program that runs on a handheld PC, the operating system (OS) performs basic tasks such as recognizing data input, sending output to the display, keeping track of files and directories on the disk, and controlling peripheral devices expansion cards. The operating system also runs all of the other programs on your handheld. The two most common handheld operating systems are Palm OS and Pocket PC.
· Operating system manufacturer: Refers to the company that develops the operating system.
· Operating system version: Refers to the version number of the operating system. Generally, the higher the number, the more recent the operating system was released. You can upgrade the operating system on some, but not all, handheld PCs.
· Processor: Short for microprocessor or CPU, the silicon chip that is at the core of all personal computers including handheld. Processors are classifled based on several features including the set of instructions that the microprocessor can execute, the number of bits of data that they can process at one time, and most commonly the clock speed.
· Processor speed: Also called the clock speed, this refers to the speed at which the processor executes instructions. The processor requires a fixed number of clock ticks (or clock cycles) to execute each instruction. The faster the clock, the more instructions the processor can execute per second. Clock speeds are expressed in megahertz (MHz), 1 MHz being equal to 1 million cycles per second. The clock speeds of processors in handheld PCs vary widely depending on the operating system. In general, the higher the value, the more powerful the processor. However, the internal architecture of the processor also affects performance.
· Rated battery life: Refers to the manufacturer's estimated battery life under normal usage conditions.
· Resolution: Refers to the sharpness and clarity of an image. For screen displays, the resolution signifies the number of dots (pixels) on the entire screen. For example, a 640-by-480 pixel screen is capable of displaying 640 distinct dots on each of 480 lines, or about 300 000 pixels.
· Touch screen: Refers to display screens that have a clear overlay that is pressure-sensitive so that you can enter instructions and data by touching the screen. Though these are less common on notebook PCs, they are virtually a requirement on handheld PCs where you use a stylus, rather than a keyboard, to enter data.
· Weight: This refers to the manufacturer's reported weight including batteries measured in ounces.
· Wireless Internet Access: Support some type of wireless access, ranging from a full-blown Internet experience, to the ability to view handheld-optimized content, such as Web clippings.