Question

Suppose a workstation has an \(\mathrm{I} / \mathrm{O}\) bus speed of \(1 \mathrm{Gbps}\) and memory bandwidth of 2 Gbps. Assuming DMA in and out of main memory, how many interfaces to 45-Mbps T3 links could a switch based on this workstation handle?

Short answer

The workstation can handle up to 22 T3 links.

Step-by-step solution

Understand the Input/Output (I/O) Bus Speed and Memory Bandwidth

The workstation's I/O bus speed is 1 Gbps and the memory bandwidth is 2 Gbps. This means the bandwidth available for data transfer to and from the memory is limited by these values.

Identify the Bandwidth Requirement for Each T3 Link

Each T3 link requires a bandwidth of 45 Mbps for data transfer.

Calculate the Total Available Bandwidth

Since DMA is used for data transfer, the total available bandwidth is determined by the lower of the I/O bus speed and the memory bandwidth. In this case, it's 1 Gbps (since 1 Gbps < 2 Gbps).

Convert Total Available Bandwidth to Mbps

Convert the total available bandwidth from Gbps to Mbps for consistency in units:1 Gbps = 1000 Mbps.

Determine the Number of T3 Links Supported

Next, divide the total available bandwidth by the bandwidth requirement for each T3 link:1000 Mbps / 45 Mbps/link ≈ 22.22.

Understanding the Result

Since the number of T3 links must be an integer, the workstation can support up to 22 T3 links, as we round down to the nearest whole number.

Key concepts

I/O Bus Speed

The Input/Output (I/O) bus speed is a critical measure for any computer system. It refers to the rate at which data is transferred between the main memory and peripheral devices. For instance, if a system has an I/O bus speed of 1 Gbps, it can handle up to 1 gigabit of data per second. This speed determines how quickly data can be read from or written to external devices, such as hard drives or network interfaces. A higher bus speed can improve performance but is often bottlenecked by other system limitations.

Memory Bandwidth

Memory bandwidth is the volume of data that can be read from or written to the memory per unit of time. It’s usually measured in gigabits per second (Gbps). In our exercise, the workstation has a memory bandwidth of 2 Gbps. This means it can transfer up to 2 gigabits of data per second between the memory and other components. Memory bandwidth is crucial for tasks that require fast data processing and transfer, such as video rendering or machine learning. However, the actual data transfer rate will be limited by the slower of either the memory bandwidth or the I/O bus speed.

T3 Link

A T3 link is a type of high-speed network connection known for its data transfer rate of 45 Mbps. It's widely used in telecommunications for digital signal transmission. In the context of our exercise, each T3 link requires a bandwidth of 45 Mbps. Therefore, understanding how many of these links a workstation can handle involves calculating the total bandwidth and dividing it by the bandwidth needed for each T3 link. These links are highly reliable and are commonly used for connecting businesses to the Internet or for interconnecting different network sites.

Data Transfer

Data transfer is the process of moving data between two or more devices or locations. In the context of our exercise, data transfer happens between the workstation's memory, the I/O bus, and the T3 links. The speed of data transfer is vital for the performance of applications that require real-time data processing. This speed is influenced by both the I/O bus speed and the memory bandwidth. When using Direct Memory Access (DMA), the CPU is bypassed, allowing data to move directly between memory and peripherals, increasing the efficiency of data transfer.

DMA (Direct Memory Access)

Direct Memory Access (DMA) is a feature that allows certain hardware subsystems to access main system memory independently of the central processing unit (CPU). This means that peripherals, like network cards or hard drives, can transfer data directly to or from memory without requiring the CPU to be involved. This can significantly speed up data transfer rates. In our workstation example, DMA is assumed, meaning data moves between memory and T3 link interfaces without CPU intervention. This efficient data flow is what enables the workstation to potentially support multiple T3 links simultaneously, up to the point where the total bandwidth is exhausted.