Physically there exist several types of scanner, each one with his advantages and his disadvantages:

• Of dessert or planes: there are the models most appreciated by his good relation price / service, although also they are of the peripheral most uncomfortable of being located due to his big size; a scanner for DIN-A4 plane can occupy almost 50x35 cm, more than many printers, with added of that almost the whole space over the same debit to stay empty to be able to open the lid.
  Nevertheless, there are the most versatile models, allowing to scan photos, free sheets, newspapers, hardbacks and even transparences, slides or negatives with the suitable adapters. The resolutions are usually raised, 300x600 ppp or more, and the quite exact price. The most common size of maximum scanning is the DIN-A4, although models exist for A3 or even major (although already with prohibitive prices).
• Of hand: there are the "portable" escáners, with everything good and the bad thing that implies this. Until a few years ago there were the only models with accessible prices for the average user, since those of dessert were extremely expensive; this situation to changed so much that at present the hand escáners are almost about to extinction. Rest in peace.
  His extinction owes to the limitations that they present as for size of the original to be scanned (generally it can be so long as love, but of little more than 10 cm wide maximum) and at his low speed, as well as to the color lack in the most economic models. What is more, almost all of them lack engine to drag the sheet, but he is the user the one that must spend the scanner on the surface to scan (to abstain those with bad pulse). All this is very bothersome, but it turns out to be effective to scan quickly photos of hardbacks, journalistic articles, invoices and all kinds of small images without the obstacle that supposes a flat scanner.

• Of roller: a few models of relatively modern appearance, base on a system very similar to that of the devices of fax: a motorized gum roller drags to the sheet, making her happen for a split where the element is placed capturador of image.
  This system implies that the originals are free sheets, what limits very much his use on not having been able to scan hardbacks without realizing earlier a photocopy (or to start the pages, if one is much a beast), except in peculiar models like Logitech FreeScan that allows to separate the reading compress and to use it as if it was a hand scanner. In favor there have the fact of occupying very little space, even exist models that integrate into the top part of the keyboard; in against tenemos that his resolution rarely overcomes them 400x800 points, although this is more than sufficient for the type of work with free sheets to which they are directed.
• Special models: apart from the hybrids of roller and of hand, other escáners destined for concrete applications exist; for example, the destined ones to scan exclusively photos, negatives or slides, devices with real resolutions of the order of 3.000x3.000 ppp that often are alike more a CD - ROM (with salver and quite) than to a classic scanner; or the pens - scanners, tools with form and size of pencil or fluorescent scoreboard that scan the text over which we spend them and sometimes even they translate it into another language to the moment; or printers - scanners similar to copiers or more individuals like the Canon, where the reader of the scanner settles like an ink cartridge.

This is one of the big questions that every future buyer of a scanner must rise to himself. The way of connecting a peripheral one to the computer is always important, so it can affect to the yield of the device, to his facility of use or installation... and fundamentally at his price, skylight.

It is the most common connection method for escáners servants, knowing as such those about intermediate - high resolution (up to 600x1.200 ppp, but more commonly of 300x600 ó 400x800 ppp) with that the speed does not have need to be very high while the price is a very important factor.

The parallel, sometimes so called port LPT1, it is the one that most of the printers uses; since generally the user already has one connected to his computer, the scanner it will have two connectors, one of entry and other of exit, so that I remained connected in the middle of the computer and the printer. As the first problem of this type of connection we have the fact that to arbitrate the use of the parallel port is something almost impossible, therefore in general we will not be able to print and scan simultaneously (although for a domestic user this should not be an excessive problem).

Anyway, we must bear in mind the fact that to obtain a reasonable speed, the port must be formed in the ways ECP or EPP (depending on the scanner in particular), which is selected generally in the BIOS. The problem appears when the computer that we want to connect is something ancient and there cannot form the port any more that in the ancient standard, 10 times slower (as it happens with the first 486 and low), or when conflicts arise with other devices that we have connected to the parallel port, like units Zip or some modern printers.

In these cases there can be worth buying a card new checker who substitutes the current port or who adds the second port (that will be LPT2); these cards checkers of devices, called also of I/O, are cheap but sometimes difficult to find for being at present integrated to the motherboard.

Undoubtedly, it is the professional option. A scanner SCSI (read "escasi") is always more expensive than his equivalent with parallel, and enclosed connector many turn out to be more expensive than models of major resolution but that use another connector. Due to this increase in price there is not made at present escáners SCSI of minor resolution of 300x600 ppp, being the most common thing that the numbers are about them 600x1.200 ppp or more.

The utility of the connection SCSI takes root in two paragraphs: speed and few requisites of microprocessor. The first thing is easy to understand: the interface SCSI can transmit from 5 to 80 MB/s, depending on the standard SCSI in particular, while the parallel port with difficulty overcomes 1 MB/s (and that in the "advanced" ways ECP or EPP). If since we saw earlier an image A4 it can occupy 25 MB or more, it turns out to be clear that a scanner SCSI is the option to be used to scan big images with a certain resolution and quality of color.

Another SCSI quality affects also in the speed, although of another form. It is not a question only of 10 being able to be transmitted ó 20 MB/s, but also the above mentioned transference is realized without the microprocessor realizing scarcely work; this allows to be scanning images while we realize other tasks, improving very much the work. In a parallel scanner it turns out to be very normal that while the scanning is realized the yield of the computer lowers so much that is not worth trying to do anything until it has finished the process.

But since not quite there are going to be advantages in this life, the escáners SCSI (and in general all the devices SCSI) have a load: his high, justifiable price for the increase of services that they suppose and for the need to include a card checker SCSI, since very few computers bring the built-in one (while they all have parallel port). To economize a little, frequently on the above mentioned card it is a model of limited services, capable of controlling only the scanner and not 7 ó 15 devices that can handle the normal cards.

This is the last thing in escáners; so much, that not long ago any more than one year simply no scanner existed on the market with this type of connection. The ports USB are present in most of computers Pentium II, AMD K6-2 or more modern, as well as in some Pentium MMX.

In general we might say that the escáners USB are located in an intermediate quality / price point. The transmission speed is about 1,5 MB/s, something more than the parallel port but enough less than the SCSI; the installation facility is almost unbeatable, since it is based on the famous person Plug and Play (to plug and listed) that almost always works; all the modern computers have the built-in USB (the normal Pentium are already ancient...: what goes to do to him!!); and also they leave the free parallel port to print or to connect other devices.

It is a question, anyway, of a solution clearly focused on the domestic user or clerk, what is evident in his price, only a little over that of the escáners of parallel port. In fact the above mentioned price difference should not exist, since to make a scanner of one or another type costs practically the same, but a recent technology they us receive the innovation from the being; it is of supposing that in a few months they cost the same that those of parallel port, which probably finish with disappearing in a few years.