Electronic books present information to the reader. Somehow that information gets presented. There is software, and this term can include the information itself, as well as the supporting control program that presents. But the software does no good without hardware.

The hardware system can range from the tiny personal digital assistant to the networked server/LAN/desktop -- with and without the Internet. It is convenient to define several classes of hardware, starting with the biggest.

1. Information retrieval system (database, port onto the Web, file server). For this class the electronic book usage of the hardware almost incidental to its other possible applications. Examples of such hardware are on-line documentation for applications, web file servers such as the MOA Journals project, the Internet Library of Early Journals, and the Gutenberg Project. Display hardware is essentially decoupled from source software, and it is the user's choice to determine how much of the source display information (resolution, color depth, layout) is represented on his monitor.

2. Local desktop machine. On-disk (hard disk, CD-ROM, DVD) documentation for application software already installed on the machine is a prime example of this case. You almost certainly have PDF versions of user manuals, text "Read Me" files, and Microsoft Help files on the machine you are reading these pages on. The quality of your display depends on the amount of money you are willing to spend on the graphics engine.

3. Laptop computer. This is a special case of the desktop machine; but, now, things are beginning to get interesting. You can carry your documents with you and examine them in remote locations. See above (2) comments on exemplars and quality of display.

4. Palmtops and Personal Digital Assistants. Here we have to trade off cost and power and weight, for speed and amount of memory and quality of display. And here there is a real gamut of hardware, from beepers with multiline displays, to Palm Pilots and Palm-sized PC's, to miniature laptops with almost full capability. Beginning in this category, we can expect specialized hardware and software tools and devices to help with the tradeoffs and make them as pleasant as possible. Examples of such external or add-on devices include external or plug-in storage devices (with or without the information already loaded, possibly for point-of-sale purchase); external displays (larger; or smaller and intended for direct-eye viewing); and external networks and network connections.

5. Specially designed and built electronic book reading devices. There are several companies selling, or working on, custom hardware for ebook reading machines. The typical such product includes

a. CPU (embedded processor)

b. RAM and ROM (and often Flash ROM)

c. control logic

d. display

e. display drive circuitry

f. user interface such as keyboard or pointing device

g. power supply

h. input/output (I/O) communication ports (optional)

i. a means of putting in new electronic texts (not optional, but it may be by use of communication ports or by plug-in module ports)

j. package and skins

k. operating system

l. application software (including user interface, text (and possibly image) rendering, display drivers, I/O drivers, and program task threads)

It's only with case 5 that we have the liberty of designing an optimal product: that ebook reader which is the most functional, the most attractive, the most easily used -- the most desirable. As designers we can trade off cost for performance; CPU processor cycle times versus power drain and battery life; cost versus display quality versus power; product size versus cost versus functionality. Throw out everything not needed in a machine that will be a book; then, whatever is left, that is your product. And just as there are many kinds of books, there are many kinds of ebooks and many kinds of ebook readers.

As discussed on the software pages, an electronic text can be as simple as a text file with standard punctuation, and as complex as an SGML-encoded art book. A monochrome display with 480 x 200 pixel resolution can handle the first case, and the second case with strain the capabilities of the biggest graphics machine in your Fortune 500 corporation. We imagine the user needs will fit a bell curve and design for the area within one or two standard deviations.

The back-of-the-envelope spec:

a. CPU with 10 to 200 MIPS (this range covers monochrome text to color PDF).

b. 4 to 16 MB of RAM and 2 to 8 MB of ROM.

c. 4 to 32 MB of allowable etext storage.

d. 4" x 6" to 8.5" x 11" display; monochrome to 24-bit color depth; illuminated or reflective or light-transmissive; active or passive pixel addressing/selection/control. One display page, or two set opposite each other (like a "real" book).

e. mechanism for inputting etext, such as serial, parallel, ethernet, scsi, USB, 1394, or IrDA port; or socket for PCMCIA card or compact-memory-module.

f. user interface controls, such as keys (or keyboard); pointing device (such as a trackball or joystick); switches.

g. power supply, preferably battery (or solar cell), but with provisions for plugging into the power grid when necessary.

h. a package that is as indestructible and environment-proof as possible, with special care taken for item (e) above.

The alert reader will have noted that the number of possibile product designs has become exceedingly large. This most likely means that several different ebook reader products can coexist in the marketplace. It's certainly going to be the case that many different products will be introduced; some much smaller number will survive and prosper. Let a thousand flowers bloom, but think of it as evolution in action.

A postscript: I originally wrote the above in September of 1998. I had expected it would have to change every few months. I was wrong. It hasn't had to change at all. I'm still waiting for the e-book reading hardware that -I- want.