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In computers, interleaving is a method of writing and reading data out of sequence. Data interleaving is used to combine multiple digital data streams, like in files that contain both audio and video. This technique is also used for memory interleave in disk storage and computer memory, used to make data read and write more quickly. A de-interleaver uses mapping to decipher the interleaved data; it is more or less a diagram of the interleaved pattern that the computer uses to decipher the data.
In media files, interleaving allows a player to quickly read audio and video data. This gives the user a single file that contains both audio and video that a properly configured media player can read and play. Reading interleaved media files often requires a codec to play the interleaved file. A codec is a software plug-in that tells a player how to read an interleaved media file. The most common interleaved media file type is Audio Video Interleave, more commonly known as AVI.
Memory interleave is a process of putting more than one data source through the same data stream in an effort to speed up processing. Interleaving is usually used for hard drives or Random Access Memory (RAM). While data is processed at the target location, the next data is being prepared by additional data sources, so more data can be processed while the first data source loads the next data in line.
To understand how memory interleave works, imagine that a ride conductor at an amusement park has two elevators that each hold four ride patrons leading up to the entrance to his ride. He loads riders quickly but doesn't have room for people to line up in the loading area. To get the riders onto the loading platform, the conductor has assistants at the bottom of the elevator accompany groups of four up to the ride, one elevator at a time. In an interleaved system, the conductor would instruct the assistant to time departures in a staggered system designed to keep the flow of riders quick and smooth. Similarly, interleaved data flows from multiple places, staggered to allow time for data sources to re-load while other streams of data process.
One disadvantage to memory interleave in data transfer is that it can cause latency. Latency is a system time delay. When one data source becomes stopped up, it affects all of the data sources using that data transfer stream, causing a slowdown in system response. Likewise, if the amusement park ride conductor has a problem loading one elevator full of riders, it will slow down both lines because he cannot process any more riders until that group has been loaded.
In older hard drives, interleaved memory was used to compensate for the hard drive reading slower than its motor spins. Data was written out of sequence to allow the hard drive time to process data while reading. Newer hard drives are designed fast enough to read data at the spinning speed, eliminating the need for memory interleaving.
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