When the UPL device address is dialed and operator pressed the load button, the system reads in 24 bytes from the device.
The first 8 bytes is a PSW. The second bytes is a CCW which read in a channel program to fetch in the system start up code. The third 8 bytes s a TIC CCW which transfer control to the new channel program read in by the previous CCW.
Once the system start up code is read in, the system will load the PSW with the first 8 bytes to start the bootstrapping.
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