20 PCI Express Interview Questions and Answers

PCI Express (PCIe) is a computer bus standard that is used to connect various components in a computer. It is a high-speed serial connection that is used to replace the older PCI and AGP bus standards. If you are interviewing for a position that involves PCIe, it is important to be prepared to answer questions about the technology. In this article, we will review some common PCIe interview questions and provide tips on how to answer them.

PCI Express Interview Questions and Answers

Here are 20 commonly asked PCI Express interview questions and answers to prepare you for your interview:

1. What is a PCIE?

A PCIE is a peripheral component interconnect express. It is a high-speed serial computer expansion bus standard.

2. Can you explain the different generations of PCI Express?

The first generation of PCI Express was released in 2004 and operated at 2.5 GT/s. The second generation was released in 2007 and operated at 5 GT/s. The third generation was released in 2010 and operated at 8 GT/s. The fourth generation was released in 2017 and operated at 16 GT/s.

3. What are some typical applications that use PCI Express?

Some typical applications that use PCI Express include:

– Servers
– Workstations
– PCs
– Laptops
– Tablets
– Smartphones
– Embedded systems
– Networking equipment
– Storage devices
– Graphics cards
– Peripherals

4. What’s the difference between PCIe and PCI-X?

The main difference between PCIe and PCI-X is that PCIe is a serial bus while PCI-X is a parallel bus. This means that PCIe can transmit data much faster than PCI-X, but it also uses more power.

5. What do you understand about ACK/NACK signals in PCI Express? How are they used?

ACK/NACK signals are used in PCI Express to indicate whether or not a particular transaction was successful. If the transaction was successful, then the receiver will send an ACK signal. If the transaction was not successful, then the receiver will send a NACK signal.

6. Is it possible to run two devices on the same lane in PCI Express? If yes, how would you go about doing so?

Yes, it is possible to run two devices on the same lane in PCI Express. You would need to configure the devices to use the same lane, and then you would need to configure the PCI Express controller to allow for multiple devices on the same lane.

7. What happens when there is a conflict during the arbitration phase in PCI Express?

When two devices on a PCI Express bus try to initiate a transaction at the same time, they must go through an arbitration process in order to determine which one gets to go first. This process is known as the arbitration phase. If there is a conflict during this phase, then the device with the higher priority will be given priority and will be able to initiate its transaction first.

8. Do all lanes support the same bandwidth in PCI Express? If not, then why not?

No, all lanes in PCI Express do not support the same bandwidth. The reason for this is that the data transfer rate is determined by the number of lanes that are being used. A lane is a pair of differential signaling wires, so a x1 connection uses one lane, a x4 connection uses four lanes, and so on. The more lanes that are used, the higher the data transfer rate will be.

9. Can you explain what PIPE stands for in context with PCI Express?

PIPE is an acronym for PCI Express Interconnect Protocol. It is the specification that defines how data is exchanged between two PCI Express devices.

10. Why are endpoints needed in PCI Express? What role do they play?

Endpoints are needed in PCI Express in order to provide a connection between the root complex and the various devices that are attached to the bus. They act as a go-between, translating requests and commands from the root complex into a format that the attached devices can understand.

11. How does an endpoint respond after receiving a completion TLP from the root port?

After an endpoint receives a completion TLP from the root port, it will first check the TLP’s header to make sure that the TLP is addressed to that endpoint. If the TLP is addressed to the endpoint, then the endpoint will process the TLP and send a response TLP back to the root port. If the TLP is not addressed to the endpoint, then the endpoint will simply ignore the TLP.

12. When should you use x16 instead of x1 in PCI Express?

The short answer is that you should use x16 when you need the full bandwidth that it provides. The long answer is a bit more complicated.

If you are using a PCI Express card that does not need the full bandwidth that x16 provides, then you can save some money by using the x1 version of the card. For example, if you are using a sound card or a network card that does not need the full bandwidth of x16, then you can save some money by using the x1 version of the card.

However, if you are using a PCI Express card that does need the full bandwidth of x16, then you should use the x16 version of the card. For example, if you are using a video card that needs the full bandwidth of x16, then you should use the x16 version of the card.

13. What are some examples of real-world products that use PCI Express?

Many computer motherboards and expansion cards use PCI Express, as do some routers and storage devices.

14. What do you understand about virtual channels in PCI Express?

Virtual channels are a feature of PCI Express that allows multiple logical channels to be multiplexed onto a single physical channel. This allows for increased bandwidth and improved efficiency.

15. What is the usage of split transactions in PCI Express?

Split transactions are used in PCI Express to allow for data to be split up into multiple transactions in order to improve performance. This is especially useful when dealing with large amounts of data that need to be transferred quickly.

16. What are posted transactions in PCI Express?

Posted transactions are transactions that are initiated by the device, rather than the host. They do not require a response from the host, and they are typically used for things like interrupts or other notifications.

17. What is your understanding of atomic operations in PCI Express?

Atomic operations in PCI Express are used to ensure that data is transferred between two devices in a safe and reliable manner. These operations are typically used when data needs to be transferred between two devices that are not connected directly to each other.

18. What is hot plugging? How is it implemented in PCI Express?

Hot plugging is the ability to add or remove devices from a system while it is still running. This is implemented in PCI Express through the use of hot plug controllers (HPCs). These controllers manage the power and configuration settings for devices that are plugged into the system, and they can also perform error checking to make sure that the devices are functioning properly.

19. How can data be transferred over multiple lanes in PCI Express?

Data can be transferred over multiple lanes in PCI Express by using a technique called lane aggregation. This allows for multiple lanes to be combined in order to increase the bandwidth of the connection.

20. What are the main differences between PCI Express and USB 3.0? Which one would you recommend using in certain situations?

The main difference between PCI Express and USB 3.0 is that PCI Express uses a point-to-point topology while USB 3.0 uses a hierarchical topology. This means that each device on a PCI Express bus has its own dedicated connection to the root complex, while USB 3.0 devices are connected in a daisy-chain fashion. In terms of performance, PCI Express is typically faster than USB 3.0, although this will vary depending on the specific implementation. In terms of power consumption, USB 3.0 is typically more power-efficient than PCI Express.

In terms of which one to use in certain situations, it really depends on the specific needs of the application. If speed is the most important factor, then PCI Express is the better choice. If power consumption is more important, then USB 3.0 is the better choice.