With personal computers, the most obvious difference is in the number of pieces that you need to have a working computer.
Mobile computers can travel; although some ultralarge laptops are not very portable, they are still self contained- a single unit.They range in size from smart phones and PDAs to 18 to 21 inch screen ultralarge portables. The ubiquitous 14 to 15 inch laptop, which actually fits on a lap, is still going strong. And all of them travel around as a one piece complete computer.
Desktop computers are typically composed of several pieces; although all in one systems generally are almost completely self contained, they are still considered desktop computers. Desktops have been appearing in ever smaller cases, and now some are available in unusual shapes or with eye-catching features as well. (Alienware has a line of cases with the classic alien features on the case, outlined in glowing blue.)
An unusual sort of small computer most people are not familiar with is the embedded computer, or single function computer.
Desktops were the first type of personal computer generally available to the consumer, aside from a few kits made by Altair and other electronic kit makers. In the early 70s a model came out which was pre-assembled, and before the end of the 70s, the Commodore PET was released.
They generally now consist of a case containing most of the computer components, a keyboard, a display, and usually a mouse or similar device. These began to be used by the public at the beginning of the 80s, and many well known companies started producing them.
Desktops developed over the years, gaining memory, speed and more and more complex operating systems (OS) which, paradoxically, tried to make it easier for the user to use the computers. This succeeded in varying degrees over the next couple decades, with many OS failing widespread adoption. Gradually, Windows came out on top, with the MAC OS trailing along- and a new OS emerging. This was Linux, a free open source OS created by volunteers. Desktops are still the most versatile of personal computers developed, because components inside the case can be changed as more powerful or different ones become available, without the need to purchase an entire new computer. Most desktop cases also come with a number of empty expansion slots where new hard drives, DVD read/write devices and other new elements can be added to augment or customize the computer.
Desktop All in Ones
One unusual exception to this is the all in one computer, such as the early MACs. They had the display built into the front of a case, with the rest of the computer parts contained in a shell behind the display. Theoretically, these could be portable, but they are considered desktops, not mobile computers. They need to be plugged into a power supply to be used. They do have another element in common with notebooks, in that they are very difficult to customize or change.
Notebooks, or Portable Computers
Notebook-like computers were available in the early 80s, but were very different from what we now consider portable computers. Some of them had no battery at all, and had to be constantly plugged into work. More commercially usable models proliferated in the early 90s, but were extremely expensive in comparison to the equivalent desktop.
Notebooks in general continue to be more expensive, because of the distinguishing feature of a notebook, or mobile computer- it comes as one unit. All of the different components that make up a computer need to be fit into a very small space- which requires specialized components sized to fit notebooks. The inside of a notebook resembles a three dimensional puzzle. Notebooks remain more difficult to assemble, despite technological advances, and they still have higher prices than desktops with the same features. Notebook prices have come down significantly, but they will probably always remain somewhat more expensive than the desktop equivalent. Notebooks are portable because they can be run off of a battery, although they come with AC converter power cords to recharge the battery and power the computer if the user is going to be in a single spot for a period of time.
Notebooks have another attribute which separates them from desktops. Except for a few items such as RAM and the size of the hard drive in the notebook, basic components can not be changed. This problem is also found in the all in one computer models. What is built into the notebook is permanently there, often with components glued to the motherboard; to get faster computers with newer features, you need to get a new notebook. Notebooks usually do have one mini PC expansion slot, so if your computer did not come with wireless capability, or you want to have Bluetooth reception, you can purchase a card to fit in the notebook and give you that capability. Your other option to provide your notebook with additional features is through your ports. Several USB ports are built into most notebooks, and you can use them to attach various augmentations or features which are not included in your notebook. For instance, if you do not have a camera in your notebook, you can get a web cam and attach it with a USB cable. This is not an ideal solution, however, because when you have three or four different attachments coming out from your notebook, it is not a mobile computer anymore. To be portable, you generally must remove your USB port attachments.
Notebooks, like desktops, can be part of a wireless network. They can do this via an Ethernet cable going to a router, or wirelessly. If your connection to the network is through a cable, you lose it every time you unplug the Ethernet cable and move your notebook.
On the next page we look at more about notebooks and other small computers.
The Amazing Expanding and Contracting Notebook
Notebooks received their name from their size and shape. They were the size of a large school notebook, and most of them folded over, covering the display, just as a notebook shut.
They have changed forms, and mutated. There are ultralarges, with 18 inch or larger screens, which can barely be described as portable. When it weighs well over 12 – 14 pounds, it no longer is very mobile. When they need to be moved, many people invest in a rolling bag to carry their ultralarge notebook around. There are sub notebooks, or mini notebooks, weighing less than the classic 14 or 15 inch screen notebooks, generally with 12-13 inch screens and often with somewhat less power or capability. Then there are sub sub notebooks, often called netbooks, whose screens range from about 7 to 10 inches and are often used just for surfing the net, sending email, or in a student’s hands, taking notes in classes. Many of these can be found weighing under a couple pounds, or a kilogram. There are tablet PCs, which often have touch screens and a complex hinge that allows the top of the tablet to turn and be folded shut like an ordinary notebook. There are PDAs, which have come from very primitive electronic calendars to multi-use devices which are emailers, calendars, smartphones and more. (Can you say BlackBerry?)
Embedded computers are meant to do a single or a few very specific tasks. However, the tasks are not always extremely simple. Multiple embedded computers can be a very cost effective way of accomplishing a complex task, by breaking down the steps into very discrete units. This can be seen as similar to the function of a CPU, which executes programs through very basic steps. However, general purpose CPUs can execute a variety of different programs, while the embedded computer is executing a single function.
Netrino.com, which call themselves the embedded system experts, provide a quote which points out both the ubiquity and importance of embedded computers:
Of the nine billion processors manufactured in 2005, less than 2% became the brains of new PCs, Macs, and Unix workstations. The other 8.8 billion went into embedded systems. The essence of every modern electronic device, from toys to traffic lights to nuclear power plant controllers, these processors help run factories, manage weapon systems, and enable the worldwide flow of information, products, and people.
Embedded processors span the range from simple 4-bit microcontrollers like those at the heart of a greeting card or children’s toy, to powerful custom 128-bit microprocessors and specialized DSPs and network processors.
Embedded computers can be very simple and in a portable device, very simple and in an immobile device, or have many discrete embedded computers in either portable or stationary devices. For an example of a large portable device; there may be numerous embedded computers in a car, doing a single task, or measuring a specific value. They have no graphical display, and generally are unable to be programmed, but your auto mechanic has a reader which can collect the output from the embedded computers in your vehicle and use the information to diagnose problems with the car. Nuclear Reactors are large and (we hope) stationary devices, and may contain many embedded computers which perform single tasks or evaluate specific measurements of how the reactor is functioning.
Your washing machine may contain several embedded computers, and nowadays repair people remove non functioning embedded units and replace them with a functioning unit to fix many problems, rather than testing various wires running from motors to other parts of the washing machine. Embedded computers even tell the repair technician where the problem unit is.
Your digital watch is another example of a computer- a very limited one with one or a few embedded computers on chips, depending on how many functions your watch has.
Source material and corrections for this article came from Eofn Williams, Henry Scudder, Michael Scudder, Lamar Stonecypher, Michele McDonough and Wikipedia. A wonderful pictorial history of computers from the early 20th century through the 80s can be found at the Computer History Museum. IBM Archives has a pictorial exhibit of the history of the IBM PC. The Commodore Computer Company, maker of the early PC the Commodore PET, is now back after many changes, producing its own line of netbooks. Netrino.com provides a detailed look at the roles of embedded computers.