Mobile Computing

4. Usability

4.1 Physical features can be as important as processing ability.

• For a PDA, size can be a critical factor. For example, if you want something genuinely pocket-sized rather than needing to carry it in a handbag or briefcase.
• The weight of a laptop can be important if you will be regularly carrying it around. Thinner, lighter laptops tend to be more expensive.
• Smaller notebook computers can weigh less, but the reduced size of the keyboard and screen may be less convenient.
• Depending on your working environment, you may need a device which is relatively durable. More rugged portables and weatherproof PDAs are available for people who work outside, for example.
• Portable computers can generate significant amounts of heat. Ensure that this is dispersed effectively (not through your lap).

4.2 The capabilities of a laptop are governed by the same specifications as a desktop computer.

For example, processor speed, amount of RAM, and size of hard disk.

• The capabilities of a PDA will depend on similar specifications, though the storage method is different. Most PDAs store everything in RAM or on memory cards, rather than having a hard disk.
• Speed, and particularly the time it takes to boot up (from switching on to being able to use the device) can be important.
• Upgrade options can be relatively restricted, particularly for PDAs. You can usually install extra memory, but only to a limited extent.

4.3 Battery life is important if you plan to use the device for a long time.

Most devices use rechargeable batteries.

• You should need to recharge a PDA at most once a day provided you switch if off when not in use.
• To use a laptop for long periods of time, you will need to connect it to the mains. Applications such as using sound and video tend to run down the batteries faster.

4.4 The size and quality of built-in displays varies.

• For laptops, high resolution screens using 'TFT' technology give the best image. A high-quality display can be the most expensive part of a portable.
• If you plan to use your laptop to show information to others, ensure that the screen provides a good image when seen at an angle.
• The small screens on PDAs can be difficult to read unless they are of good quality.

4.5 Input devices can have a significant effect on usability.

• The built-in keyboards of portable computers vary in size and quality. Even the largest, high quality keyboards are rarely as easy to use as the keyboard for a desktop computer.
• Most PDAs use a stylus, and a form of handwriting recognition, to input data. This should be easy to use, but may require some practice and will not be quick for large amounts of text.
• Some PDAs offer miniaturised built-in keyboards, or larger keyboard attachments as an option. These generally only allow you to type slowly, with one finger.
• Tablet PCs are similar to laptops, but use a handwriting recognition system like a PDA. Other input devices which work in a similar way, but for use with standard laptops, are becoming more widely available.
• Portables use devices such as touch pads and rollerballs rather than a mouse. Some users find these less easy to control.

4.6 The only way to get a realistic assessment of usability is to try it. Bear in mind that weaknesses which may be acceptable in a quick test can become major irritants or problems later on. For example:

• A laptop which is easy to pick up will seem much heavier if you have to carry it for a mile.
• Waiting for a machine to boot up will be more frustrating if you have a client waiting with you.