What is the difference between a laptop computer, a portable computer and a notebook computer? My definition is that a laptop can be used comfortably on the user's lap or knees for extended periods of time. A portable computer is one that can be carried from A to B without too much trouble. A notebook is a computer that has a lid, with keyboard in the base of the casing and enclosed when shut by a hinged top that carries the LCD screen. A decade ago, portable computers were rugged PCs with sturdy metal handles used by people who needed to compute in strange places. They came in beige-coloured, fibreglass or metal casings. The shapes were designed not for easy usage but for easy storage. Portable does not always mean light. I have seen a technology company use one for sales demonstrations only recently. They simply update the motherboard inside and plug in an external keyboard and monitor. The casing was chipped and marked but two of them fit nicely inside the cabin baggage restrictions adopted by most airlines, so it is easy to transport them. They are also tough enough to be put through the mangler of the international check-on baggage system in most airports. They weigh up to eight kilograms each, certainly not in the lightweight category. There are few true laptop computers still available. The Tandy TRS and Sinclair ZX-80, two of the best laptops ever built, are more than a decade old. Models of these are still in use. They are mainly used to transfer pure text from one point to another via a telephone line, using one of those telephone handset coupler modems that depended upon a round ear-piece and round mouthpiece, so the suction cups on the modem could clamp on to both ends of the telephone handset. The chip that controls the data flow in the modem port cannot cope with throughput beyond 300bps (bits per second). It was frustrating to watch the words dribble through at a speed comparable with typing pace. They ran with AA batteries for weeks and weeks. The screens were early monochrome with very little distinction between different shades of grey. The computers were flat, like an elongated version of a pocket calculator, had a qwerty keyboard and a shallow screen showing a few lines of text at a time. The Sinclair has rubber keys, which make for silent typing. They were great for rattling out lots of words when you were away from the office. I know of one eccentric journalist who liked the Sinclair so much that two years ago he made moves to take over the company that produced them, even though turnover was quite modest. A modern-day Pentium or 486 notebook computer, which has the screen encased in the flip-up lid, is not a laptop in my book. The true test is whether it is comfortable to use on your lap. Laptop computing is what people do in short bursts on trains and aircraft and in taxis, in waiting rooms and lounges. The early 386-based notebooks could be used comfortably on the lap. They had monochrome screens, were fairly small and they did not run too hot. The notebook trend has been towards bigger screens and faster chips that run hotter, both in terms of temperature and performance. The bigger screens mean that often the computer over-balances when you have it on your knees. That has happened to me several times and it is quite nerve-wracking in that moment when you pick up the computer from the floor to find out if it still works. The higher-powered chips mean that the batteries work hard to supply the electricity and your knees get very hot. It is just not comfortable to put a colour screen Pentium computer on your knees for more than 15 minutes at a time. Even a thick magazine or newspaper does not insulate adequately. A laptop also has to have the capability of instant on and instant off. If you are working on an aircraft and the stewardess approaches menacingly with a cup of coffee, you feel obliged to shut up the PC for a few moments to accept the terrible beverage. I was working on a story with my new PC recently in exactly that situation and I lost all my work. It did not save. It did not send the computer into sleep mode. I was rather annoyed. Sometimes it is handy to be able to type or read urgent messages while you are in a traffic jam. Instant on is a must in a laptop, or else you waste too much time booting up to make it worthwhile.