What is the difference between PCI and PCIe slots?

PCI is the abbreviation of Peripheral Component Interconnect (standard for connecting peripheral components). It is the most widely used interface in PCs, and is available in almost all motherboard products. PCI slots are also the most frequently used slots on the motherboard. on popular desktop boards, The ATX motherboard generally has 5 ~ Six PCI slots, and a smaller matx motherboard also has 2 ~ The three PCI slots show their wide application.

PCI is a local bus launched by Intel in 1991. In terms of structure, PCI is a level-1 bus inserted between the CPU and the original system bus. A bridge circuit is used to manage this layer, it also implements interfaces between upstream and downstream to coordinate data transmission. The manager provides signal buffering to support 10 peripherals and maintain high performance at high clock frequencies. It provides connection interfaces for devices such as video cards, sound cards, NICS, and modem, it operates at 33 MHz/66 MHz.

The earliest proposal of the PCI bus worked at 33 MHz and the transmission bandwidth reached 133 Mb/s (33 MHz x 32 bit/8), basically meeting the development needs of the processor at that time. With higher performance requirements, 64-bit PCI bus was proposed in 1993, and later the frequency of PCI bus was increased to 66 MHz. Currently, the 32-bit and 33 MHz PCI bus are widely used, and 64bit PCI slots are mostly used in server products.

Because the PCI bus only has 133 Mb/s bandwidth, most input/output devices, such as sound cards, network cards, and video cards, are more than enough. However, the increasingly powerful graphics card cannot meet its needs. Currently, the graphics card of PCI interfaces is rare and only available on older PCs, and vendors seldom launch such interfaces. Of course, many servers do not need good graphics card performance, so they use the old PCI graphics card. PCI graphics cards are generally used only on boards that do not have a dedicated card slot (such as AGP or PCI Express), for example, to upgrade the 845gl motherboard. The performance of the PCI video card is greatly limited, and the quantity is scarce, so the price is not cheap. You can only consider using the PCI video card as a last resort.
PCI-E interfaces vary based on bus bit width, including X1, X4, X8, and x16, while X2 mode will be used for internal interfaces instead of Slot Mode. The PCI-E specification is connected from one channel to 32 channel connections, with very strong scalability to meet different system equipment for different data transmission bandwidth needs. In addition, the shorter PCI-E card can be inserted into the longer PCI-E slots used, PCI-E interface can also support hot plugging, which is not small leap. The 250 Mb/s transmission speed of PCI-E X1 can meet the requirements of mainstream sound effect chips, Nic chips and storage devices for data transmission bandwidth, however, it is far from able to meet the data transmission bandwidth requirements of graphics chips. Therefore, the PCI-E interface used to replace the AGP interface is x16, can provide 5 Gbit/s bandwidth, even if there is a loss in coding, it can still provide about 4 Gbit/s of actual bandwidth, far exceeding the 2.1 Gbit/s bandwidth of the AGP 8x.

Although the PCI-E specifications allow for x1 (250 Mbit/s), X2, X4, X8, X12, x16, and x32 channel specifications, as currently, PCI-E X1 and PCI-E x16 has become the mainstream specification of PCI-E, while many chipset manufacturers in the south bridge chip to add support for PCI-E X1, in the North Bridge Chip to add support for PCI-E x16. In addition to providing extremely high data transmission bandwidth, since PCI-E transmits data in the form of serial packets, each pin of the PCI-E interface can obtain more bandwidth than the traditional I/O standard, this can reduce the production cost and volume of PCI-E equipment. In addition, the PCI-E also supports High-Order Power Management, supports hot swapping, supports synchronous data transmission, bandwidth optimization for priority transmission data.

In terms of compatibility, the PCI-E is compatible with the current PCI technology and equipment at the software level, supporting the initialization of PCI devices and memory modules, that is to say, the past drivers, operating systems do not have to be replayed, to support PCI-E devices. At present, the PCI-E has become the mainstream of the video interface, but some early chipset although provide PCI-E as the video interface, but its speed is 4x, rather than 16x, for example, via pt880 pro and via pt880 ultra are rare.