Expansion BUS slots
It would be impossible or expensive to build a
computer that fits every user application. To fix this, PC designers include
standardized connectors that enable users to configure the system to their
particular computing needs.
Most PCs use what is called EXPANSION BUS SLOT connectors to help
connect various types of peripheral devices to the system. Interface adapter
cards are plugged into these slots to connect the devices to the system’s
address, data and control buses (these
are the three basic channels of information contained in the adapter card used
to carry out data transfer between the system and the peripheral device).
This is a means through which the system board communicates with the various
optional I/O and memory systems. The slots are located along the left rear
portion of the system board so that the external devices they serve can access
them through openings at the rear of the case.
The expansion slot supplies the power required
to operate the adapter card circuitry. However, different expansion slot types
employ different connection layouts, timing, speed requirements, and operating
signal levels. Therefore, you should be aware that given adapter cards can only
be used in slots they are designed for. So it is important to know which type
of slot is available when dealing with adapter cards.
Note – A
particular system board may contain only one type of slot, or mixture of the
expansion slot types. The following expansion slot types are commonly found on
Pentium-class system boards.
1. PCI (Peripheral Component Interconnect)
Slots – These 32/64-bit slot have been the most widely used
expansion slots in the Pentium PC environment replacing the 16-bit ISA
(Industry Standard Architecture). They conduct data transfers at rates between
132 and 528MBps.
2. AGP (Accelerated Graphics Port) Slot –
This is a 32-bit derivative of the PCI bus. It was developed to provide
interface for advanced VGA (Video Graphics Adapter). Data pass back and forth
at rates of up to 2.1GBps
3. AMR (Audio Modem Riser) Slot –
This is developed to handle specialized modems and sound cards that interacts
directly with the system.
4. CNR (Communications and Networking Riser)
Slot – This was developed to replace the AMR slot. It is
designed to handle special communication and audio cards.
5. PCI extended (PCI-X) Slots –
These have a high performance version of the original PCI bus specification but
maintained the same connectors. They employed advanced signaling techniques to
provide performance levels of 266 and 533MHz and data transfer rates up to 2.1
and 4.3GBps.
6. PCI express (PCIe) Slots –
These have a collection of high-speed serial versions of the PCI bus standard.
They possess slot specifications that are not compatible with other PCI
devices. They push performance levels to 2.5GHz and data transfer rates to
between 250MBps and 4GBps.
The least expected is the ISA (Industry Standard Architecture) slot also known as the Advanced
Technology (AT) but you may still encounter this 16-bit slot. Unlike
others, it is non-plug and play; it is a legacy slot on older Pentium system
boards. It has served as a standard expansion slot specification for many years
and through several generations of processors. The ISA slot ran at 8.33MHz and
could transfer data at a whopping of 8MBps.
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