When a new request arrives while the drive is idle, the initial arm/head movement will be in the direction of the cylinder where the data is stored, either in or out.
Although the time of the return seek is wasted, this results in more equal performance for all head positions, as the expected distance from the head is always half the maximum distance, unlike in the standard elevator algorithm where cylinders in the middle will be serviced as much as twice as often as the innermost or outermost cylinders.
Other variations include: The following is an example of how to calculate average disk seek times for both the SCAN and C-SCAN algorithms.
By using the scan algorithm, you efficiently compute these cumulative results in a single pass over the data.
Use Cases Beyond Stock Market Analysis: Image Processing: Cumulative operations (like pixel intensities) for tasks such as convolution or blur filters.
The scan algorithm is essential in scenarios where you need to process or aggregate data in a way that builds on prior computations, and its parallel implementation helps in scaling up for larger datasets.
For both versions of the elevator algorithm, the arm movement is less than twice the number of total cylinders and produces a smaller variance in response time.