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Slots on the PC main board (below), expansion card with contact surfaces (above)
Mainboard with different slots, left from top to bottom: 1 × COAST , 3 × PCI , 1 × PCI + ASUS Media Bus , 1 × ISA , 4 × EISA ; right: 8 × SIMM

In electronic devices designated slot or slots (engl. For slot , place ) a mechanical and electrical interface , in which further components may be inserted to expand the device or modular to make. A typical example is the personal computer whose motherboard has slots for memory expansions , expansion cards and possibly the processor .

The term slot is used especially for slots with direct connectors (card-edge connector). In this case, the expansion component consists of a printed circuit board , the conductor tracks of which form contact areas on one edge. This side of the circuit board is then plugged into the slot-shaped plug-in coupling ("slot") on the opposite side. Direct plug-in connections are very cost-effective because the expansion card itself does not require a connector. Such a circuit board is also referred to as a plug-in card .

The mechanical and electrical properties of the different slots are defined in a large number of norms , industry standards and proprietary specifications .

Memory expansion

In PCs , the main memory is implemented with memory modules . As technology advances rapidly in this sector, a variety of standards exist for memory and its slots. The most important designs and associated storage technologies are

Due to extreme mass production , these memories are very inexpensive and are therefore also used by many other devices (e.g. printers ).

More compact designs, such as. B. are necessary in notebooks include

  • SO-DIMM with 72 or 144 contacts for SDRAM , 200 contacts for DDR-SDRAM
  • Micro-DIMM with 214 contacts for DDR2-SDRAM
  • SO-RIMM with 160 contacts for RDRAM

Expansion cards

PCs have a modular structure and can be expanded using various bus systems . A distinction can be made between general slots that can be used for different purposes and special slots for dedicated applications (such as graphics cards ). In general, however, the importance of expansion cards is decreasing, since on the one hand more and more functions are integrated on the motherboard (e.g. sound cards , network cards ) and, on the other hand, many expansions are connected as external devices with a cable via USB or FireWire (e.g. modem ).

Current PCs typically have multiple slots in one of the following systems:

  • PCI , the standard bus in today's PCs
  • PCI-X , a more powerful extension of PCI
  • PCI Express (PCIe, PCI-E) in different variants, for example PCI-Express x1 as a planned replacement for PCI and PCIe x16 as a replacement for AGP

Older PCs have standard slots

In addition to the slots mentioned above, there is often

  • AGP , a single slot for a graphics card
  • VESA Local Bus (VLB), an extension (extension) of ISA slots, mainly used for graphics cards and only available on the market for a few years
  • CNR , mainly used by OEM manufacturers for modem cards.

Many PCs have a combination of different slots, for example several PCI slots and an AGP slot.


PC microprocessors are usually interchangeable. For this purpose, a pin grid array that fits into a processor socket on the motherboard is usually used as the IC housing . Some processor models are soldered (together with cache memory) onto a small printed circuit board that fits upright in a dedicated slot. Common slot types and the corresponding processors are