As satellite-based navigation systems take over tedious steering chores, multitasking farmers are adding computers to their tractor and combine cabs, allowing them to e-mail, text and surf their way across the field. While it’s possible to fit a full-size laptop computer into a crowded cab, sub-sized netbooks and tablet computers can be easier to handle. Smartphones are an even more popular alternative, but their small screens can be limiting.

Since coming on the market in 2007, netbooks (so-named because they were marketed primarily for accessing the Internet) have become more powerful and larger compared to early 7-in. models. While still slow by laptop computer standards, the latest netbooks pack more processing power and come with screen-size options ranging from the single to low double digits.

Tablet computers have existed in various forms for two decades or more, but Apple’s iPad touch-screen tablet is the first to take off in a big way commercially. In the first 80 days after the iPad’s April 2010 release, Apple boasted it had sold 3 million of the tablets.

One analyst estimates that iPad sales could reach 16 million in its first year, roughly double the netbook sales record in that category’s first 12 months. But Apple won’t have the market to itself for long. Additional tablets using Google’s Android and Microsoft’s Windows 7 operating systems are expected to be on the market by year’s end, or early 2011.

Netbooks are available from myriad manufacturers. Recent introductions featured here are from Asus, an early netbook innovator, and industry stalwart Hewlett Packard. Both are powered by 1.66-gigahertz (GHz) Intel Atom N450 processors typical of the latest generation of netbooks, and use the Windows 7 Starter operating system

Asus Eee PC 1018PB

The Asus Eee PC 1018PB features a 10.1-in. LED screen housed in a metal clamshell chassis that measures 10.3 x 7.1 x .9 in. and weighs 2.5 lbs. Unlike smaller Asus netbooks, which have solid-state storage drives, this larger model has a 250-gigabyte (GB), 5,400-rpm hard drive with 1 GB of random access memory (RAM). The keyboard is slightly undersized, typical of netbooks. The list price for a base model is $349. For more information, visit usa.asus.com.

HP Mini 210

The HP Mini 210 also features a 10.1-in. LED screen and an island-style keyboard that’s 92% the size of a standard laptop keyboard. A brighter wide-screen display is optional. The case, which comes in black, silver, blue or red, measures 10.55 x 6.9 in. x 0.9 to 1.11 in. and weighs 2.69 lbs. It supports up to 1 GB of RAM and hard drives as large as 320 GB. A base model lists for $329. For more information, visit www.hp.com

Apple iPad

The Apple iPad uses Apple’s custom 1-GHz A4 processor and Apple’s iOS 4
operating system, also used on the iPhone and iTouch. It boasts thousands of free and low-cost applications — 14,000 and counting for the iPad, plus more than 140,000 iPhone applications. If you want Windows compatibility, it’s not for you, but it’s ready to surf the Web, serve as a pdf reader for electronic parts manuals, and more.

The iPad features a multi-touch 9.7-in. LED backlit display housed in a 7.5- x 9.5 x .5-in. chassis that weighs just over 1.5 lbs. Since the screen takes up all the real estate, an on-screen virtual keyboard is used for writing e-mails and notes. Prices range from $499 for a wireless-only model with 16-GB solid-state drive, to $829 for a 64-GB wireless/3G model. Like the iPhone, the iPad is available for use only through the ATT cellular network. For more information, visit www.apple.com.