Shutdowns at Latcc (West Drayton), now called something different at Lacc (Swanwick). This is when the engineers turn off the computer that generates all our information, so we have to go 'manual'. All it means is that the estimates to other ACC's and agencies have to be passed by phone as the 'computer link' no longer works. Also, all the radar tools, such as conflict alert, are lost. If it goes on for some time, it can also lead to our flight strips being written by hand, as most of the first 4 hours of traffic have 'skeleton' strips printed where we just fill in Squalk, FL, and times.
The computer has to be shut down to clear out all the files. When pending plans aren't activated, they are still kept in the memory, so eventually it gets full. It happens usually on Wednesday nights between 1030pm and 3am, just as its getting quiet at night, and back on to take the Atlantic fallout around 330am. Sometimes they happen on other nights too, as the engineers also use them to install and update the software.
Hope that helps, and hope I got it all right too!!!!!