Most cases are designed to let you attach external devices, such as printers, external modems, and mice, via connectors on the back panel of the case. There are three types of connectors commonly used, from the point of view of the case:
• Motherboard-mounted connectors As described in Chapter 2, all x86 motherboards have at least one connector permanently attached: the keyboard connector. Motherboards based on ATX and its variants support additional connectors, typically including serial, parallel, USB, and PS/2 mouse ports. The case includes appropriate openings to allow these connectors through, provided the case is designed for the motherboard type you use.
• Card-mounted connectors Plug-in adapter cards, such as video cards, sound boards, and Ethernet cards, often include external connectors, or ports, as illustrated by the sound card in Figure 4.7. The vast majority of ATX cases have sufficient cutouts on their backs to accommodate all ATX motherboards, but on occasion you'll find an AT-style case with insufficient space for the slots on its motherboard.
in a case, the four connectors in the foreground of this card are accessible from the rear
When inserted puter case.
in a case, the four connectors in the foreground of this card are accessible from the rear of the com-
The rear panel on which connectors mount is the same for all types of cards used in standard x86 cases. Therefore, the case doesn't need to be designed for ISA versus PCI slots, for example. In fact, it's possible to remove an all-ISA motherboard from a case and replace it with an all-PCI motherboard.
• Cable-linked connectors Many cases include regions on their back panels that you can punch out to accommodate external connectors that link to internal connectors via ribbon cable. Such punch-out areas are particularly common on older AT-style cases, because the matching motherboards used ports that linked to external connectors via ribbon cables. Such punch-out openings are sometimes useful even on ATX systems, however. For example, the internal/external SCSI adapter described in Chapter 2 and shown in Figure 2.14 can connect through such a punch-out adapter. If your case lacks such openings, you can use an adapter that fits into an opening intended for an expansion card slot that you're not using.
Most motherboards have adequate back-panel cutouts, although the punch-out areas for cable-linked connectors are most common on larger case sizes. A few cases, particularly custom designs for major computer manufacturers, move one or more adapters to the front panel of the computer. USB and game port adapters are most likely to find their way to the front of such computers.
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