Question

what is interleaving?

Answer 1

interleaving is a way to arrange memory in a non-contiguous way to increase performance.

Example
Information is commonly stored on disk storage in very small pieces referred to as sectors or blocks. These are arranged in concentric rings referred to as tracks across the surface of each disk. While it may seem easiest to order these blocks in direct serial order in each track, such as 1 2 3 4 5 6 7 8 9, for early computing devices this ordering was not practical.
Data to be written or read is put into a special region of reusable memory referred to as a buffer. When data needed to be written, it was moved into the buffer, and then written from the buffer to the disk. When data was read, the reverse took place, transferring first into the buffer and then moved to where it was needed. Most early computers were not fast enough to read a sector, move the data from the buffer to somewhere else, and be ready to read the next sector by the time that next sector was appearing under the read head.
When sectors were arranged in direct serial order, after the first sector was read the computer may spend the time it takes for three sectors to pass by before it is ready to receive data again. However with the sectors in direct order, sector two, three, and four have already passed by. The computer doesn't need sectors 4, 5, 6, 7, 8, 9, or 1, and must wait for these to pass by, before reading sector two. This waiting for the disk to spin around to the right spot slows the data transfer rate.