Currently, the most common type of expansion slot available is called PCI Express.
In this tutorial, you will learn everything you need to know about this kind of connection: how it works, versions, slots, and more.
Before talking about the PCI Express, we must talk a little bit about the history of PC expansion slots and their main challenges, so you can understand what makes the PCI Express different.
For example, the original ISA slot available on the original IBM PC and on the IBM PC XT and their clones, had a maximum theoretical transfer rate i.
So, the MCA slots were confined to a few PC models from these brands.
First, it maintained compatibility with the original ISA slot, so its what are the bonus in rate was the same as the 16-bit ISA slot.
The first real high-speed slot to be released was the VLB.
The higher speed was achieved by tying the slot to the CPU local what are pci express x4 slots used for, i.
This way, the slot worked at the same speed as the CPU external bus, which is the fastest bus available on the PC.
In the table below, we are listing this slot as using a 33 MHz clock rate, but the actual clock rate will depend on the CPU used.
Most CPUs at the time used a 33 MHz external clock rate, but CPUs with 25 MHz and 40 MHz external clock rates were also available.
The problem with this bus was that it was designed specifically for the local bus of 486-class processors.
When the Pentium processor was released, it was incompatible with it, as it used a local bus with different specifications 66 MHz external clock rate instead of 33 MHz and 64-bit data transfers instead of 32-bit.
Later, other companies joined the alliance, which is known today as PCI-SIG PCI Special Interest Group.
The PCI-SIG is responsible for standardizing the PCI, PCI-X and PCI Express slots.
Even though these names are similar, they refer to completely different technologies.
The PCI is a platform-independent bus that is connected to the system using a bridge chip which is part of the motherboard chipset.
Whenever a new CPU is released, you can still use the same PCI bus by redesigning the bridge chip instead of redesigning the bus, which was the norm before the PCI bus was created.
A bus is a data path where you can attach several devices at the same time, sharing this data path.
The most obvious devices attached to the PCI bus were expansion slots, but integrated components available on the motherboard such as an on-board network chip could be connected to the PCI bus.
The PCI-X bus is a version of the PCI bus working at higher clock rates and with wider data paths for server motherboards, achieving higher bandwidth for devices that demanded more speed, such as high-end network cards and RAID controllers.
This slot was used exclusively for video cards.
Despite its name, PCI Express works radically different from the PCI bus.
PCI is a bus, whereas PCI Express is a point-to-point connection, i.
On a motherboard with PCI Express slots, each PCI What are pci express x4 slots used for slot is connected to the motherboard chipset using a dedicated lane, not sharing this lane data path with other PCI Express slots.
Also, devices integrated on the motherboard, such as network, SATA, and USB controllers, are usually connected to the motherboard chipset using dedicated PCI Express connections.
PCI and all other kinds of expansion slots use parallel communications, while PCI Express is based on high-speed serial communications.
PCI Express is based on individual lanes, which can be grouped to create higher-bandwidth connections.
The PCI Express connection is the subject of this tutorial.
We will go into more detail about how it works in the following pages.
Below is a table comparing the main specifications for the expansion slots that ever existed for the PC.
Slot Clock Number of Bits Data per Clock Cycle Bandwidth ISA 4.
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