Towers, Mini-Towers, Desktops
Although it is relatively unimportant, there lie a few distinctions in classifications of PC cases. The case of the PC is the exterior body, or the enclosure, of the motherboard and all connected components. This includes the power supply, cooling equipment, hard drives, optical drives, and any expansion cards. The vast majority of cases today are beige, mid-tower ATX enclosures known as a “beige box” to describe the generic qualities of this case (this is not to be confused with the phone-hacking term “beige box” as I am sure there is an enlightened person reading this with some other connotations in mind concerning the term). There are some general and some more specific classifications regarding all cases. The first classification is by one of three basic types: towers, mini (or mid) towers, and desktops. Most standalone servers come in large towers, which sit upright and are generally very large to accommodate a large number of hard drives, cooling equipment, and dual processors. Some high-end workstations and gaming rigs these days are enclosed by full towers. Mid-Towers are like towers in that they sit upright, but are generally smaller in depth, length, and height. The vast majority of computers these days are mid-towers. The third class is the desktop. This is a computer that lies flat on the desk, usually with the monitor on top of it. Although most consumer PC’s no longer utilize this enclosure, many corporate computers use this space-saving design.
There is also another widely-known means of classification – by motherboard form factor. However, motherboard form factor has much more relevance than just in the physical sense.
Motherboard Form Factors
There are a multitude of motherboard “form factors.” Form factors of a motherboard describe the physical shape and appearance, as well as features and circuitry, of a motherboard. There are newer and older form factors, as there are newer and older computer components.
XT
The XT, or extended technology, form factor was developed for the Intel 8088 CPU. All you need to know about this is that it is very, extremely old. It utilizes a 16-bit internal and 8-bit external bus. The XT form factor also could not be configured electronically – rather, to configure BIOS settings, you would have to manually set jumpers.
AT
Advanced Technology, or AT boards were the next step up from XT motherboards. Though physically (dimensionally) the same as its predecessor, the AT form factor motherboard is distinguished by a number of features. The first of these is a 16-bit (or in some cases, greater) external bus. It is important to understand what is being referred to when a bus is called “16-bit” or “32-bit.” The width of the bus, known as the datapath, is measured in bits. One bit represents a single digit, one or zero, in the binary system. With 8 bits, one can form 8 1’s or 0’s. Correspondingly, those 8 digits can form a number between 0 and 255 in the decimal system. The greater the size of the datapath, the more information can be pushed from one system component to another, including such things as hard drives and expansion cards. A serial bus, for example, transfers information serially, that is, one bit at a time, whereas the parallel bus transfers information at eight bits at a time. Make careful mention that although the datapath of one bus may be larger than another, this does not make the former faster than the other. For example, USB is a serial bus, yet transfers information hundreds of times faster than an eight-bit parallel bus. In addition to the 16-bit external bus, AT utilizes a keyboard connector that has five pins and is larger than the PS/2 keyboard connector that will arise in the future. This five-pin DIN connector would come to be known as the AT connector, synonymous with “old keyboard connector.” This is because the AT form factor is a number of years older than the more modern form factors. The last major advantage of AT over XT was its use of CMOS – Complimentary Metal Oxide Semiconductor – in configuring BIOS – Basic Input Output Settings – in the place of jumpers and switches.
Baby AT
The Baby AT board was a response to those manufacturers and consumers who longed for a smaller yet similarly capable form factor. Thus the Baby AT factor was born.
LPX/Mini-LPX
Although the Baby AT motherboard form factor was very slim, it still was not quite small enough to fit into a slimline desktop unit. To alleviate this, the LPX and Mini-LPX form factors were utilized and although they share many features with the AT design, they also have a few advantages over it. One, of course, is obviously physical shape and size. The AT board was more than twice as big in area! Less obvious is the ability for the LPX and Mini-LPX boards to use a riser card, which allows all of the expansion cards to lie flat, rather than tall. This reduces the height of the desktop by the width of the riser card. In addition, the connectors on these motherboards were in well-fitting, standard placements. Because the AT five-pin DIN connector was too large, a smaller and more versatile six-pin Mini-DIN connector was created. This was to be deemed the PS/2 connector.
ATX/Mini-ATX
The majority of today’s PC’s utilize the ATX form factor. Smaller dimensionally than the AT form factor, and with many more features, the ATX form factor is practical in today’s PC applications. First of all, it is physically smaller and eliminates drive overlap in most cases. Second, all of the I/O connectors are built right into the board. Third, the ATX utilizes the PS/2 keyboard connector. Fourth, the CPU placement and cooling options are designated for a cooler computing experience. Fifth, there is a single 20-pin power connector. Finally, the ATX form factor runs at a lower voltage than before, 3.3V, which is now an accepted computer component standard.
NLX
NLX is basically the update to the LPX and Mini-LPX corresponding to ATX. It is found in newer retail slimline and desktop PC’s.
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