Microcontrollers

Microcontrollers, also called embedded computers, are the tiny, specialized microprocessors installed in "smart" appliances and automobiles. These microcontrollers enable, for example, microwave ovens to store data about how long to cook your potatoes and at what temperature.

Microcomputers: Personal Computers

Microcomputers are small computers that can fit on or beside a desk or are portable. Microcomputers are considered to be of two types: personal com­puters and workstations.

Personal computers (PCs) are desktop, tower, or portable computers that can run easy-to-use programs such as word processing or spreadsheets. PCs come in several sizes, as follows.

Even though many personal computers today are portable, buyers of new PCs often opt for nonportable systems, for rea­sons of price, power, or flexibility. For example, the television-tube-like (CRT, or cathode-ray tube) monitors that come with desktops have display screens that are easier to read than those of many portables. Moreover, you can stuff a desktop's roomy system cabinet with add-on circuit boards and other extras, which is not possible with portables.

Desktop PCs are those in which the system cabinet sits on a desk, with keyboard in front and monitor often on top. A difficulty with this arrange­ment is that the system cabinet's "footprint" can deprive you of a fair amount of desk space. Tower PCs are those in which the system cabinet sits as a "tower" on the desk or on the floor next to the desk, giving you more usable desk space.

· A laptop computer is a portable computer equipped with a flat display screen and weighing 8-20 pounds. The top of the computer opens up like a clamshell to reveal the screen.

We describe the differences between display screens elsewhere. Here we will simply say that flat screens don't provide the quality of the monitors found with desktop computers (although that is changing). However, most laptops can be hooked up to standard desktop-type monitors so that you don't lose display quality.

* Notebooks: A notebook computer is a portable computer that weighs 4-7.5 pounds and is roughly the size of a thick notebook, perhaps SVz by 11 inches. Notebook PCs can easily be tucked into a briefcase or back­pack or simply under your arm.

Notebook computers can be just as powerful as some desktop machines. However, because they are smaller, the keys on the keyboards are closer together and harder to use. Also, as with laptops, the display screens are more difficult to read.

* A subnotebook computer weighs 2.5-4 pounds. Clearly, subnotebooks have more of both the advantages and the disadvantages of notebooks

· Pocket personal computers, or handhelds, weigh about 1 pound or less. These PCs are useful in specific situations, as when a driv­er of a package-delivery truck must feed hourly status reports to company headquarters. Another use allows police officers to check out suspicious car license numbers against a database in a central computer. Other pocket PCs have more general applications as electronic diaries and pocket orga­nizers.

Pocket PCs may be classified into three types:

(1) Electronic organizers are specialized pocket computers that mainly store appointments, addresses, and "to do" lists. Recent versions feature wireless links to other computers for data transfer.

(2) Palmtop computers are PCs that are small enough to hold in one hand and operate with the other.

(3) Pen computers lack a keyboard or a mouse but allow you to input data by writing directly on the screen with a stylus, or pen. Pen computers are useful for inventory control, as when a store clerk has to count merchandise,- for package-delivery drivers who must get electronic signatures as proof of delivery; and for more general purposes, like those of elec­tronic organizers and PDAs.

Personal digital assistants (PDAs), or personal communicators, are small, pen-controlled, handheld computers that, in their most developed form, can do two-way wireless messaging.

We explain more about notebooks, subnotebooks, and pocket PCs, and their usefulness, in the Experience Box at the end of this chapter.

What is the one thing besides their light weight that makes portable com­puters truly portable? The answer: batteries. A typical notebook's batteries will keep it running about 3-5 hours, a subnotebook's about 3 hours. The record holder seems to be 8 hours and 45 minutes on a standard nickel metal hydride battery.⁸ Then the PC must be plugged into an AC outlet and charged up again. Some travelers carry spare battery packs.

In the works is a zinc-air battery that can run a laptop for up to 12 hours without a recharge. However, refinements are still being made.

Microcomputers: Workstations

Workstations look like desktop PCs but are far more powerful. Traditionally, workstations were sophisticated machines that fit on a desk, cost $10,000-$150,000, and were used mainly by engineers and scientists for tech­nical purposes. However, workstations have long been used for computer-aided design and manufacturing (CAD/CAM,), software development, and scientific modeling. Workstations have caught the eye of the public mainly for their graphics capabilities, such as those used to breathe three-dimensional life into toys for the movie Toy Story.

Two recent developments have altered the differences between worksta­tions and PCs:

* Decline in workstation prices. A workstation that not long ago cost $15,000 or more is now available for under $5000, which puts it within range of many PC buyers.

* In 1993 Intel introduced the Pentium chip - in 1994 Motorola (with IBM and Apple) introduced its PowerPC chip. Both of these very powerful microprocessors are now found in PCs. In addition, Microsoft introduced Windows NT, the first operating system designed to take advantage of more powerful microprocessors.

You might deduce from this that, if PCs are becoming more powerful, then workstations are becoming more powerful still—and indeed they are. Over the past 15 years the fastest workstations have increased in speed a thou­sand fold. They have been cutting into the sales not only of minicomput­ers and mainframes but even of supercomputers. These large machines have become vulnerable particularly since workstations can now be harnessed in "clusters" to attack a problem simultaneously

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