More recently introduced terms such as 'annually laminated' are synonymous with varve. Of the many rhythmites in the geological record, varves are one of the most important and illuminating in studies of past climate change. Varves are amongst the smallest-scale events recognised in stratigraphy.
PCs are designed to shut down automatically when heat endangers the hardware. To find out if this is your problem, download and install Speedfan. It's small and free. Although Speedfan's basic job is controlling the speed of your PC's fans (you probably guessed that by the name), it also provides the CPU temperature.
If the memory is more on the RAM, then the computer does not need to use much of the hard drive. When the computer is on and active, then the information stored on the RAM is running, once the machine is shut down, then it disappears. If your RAM is not working well, you will get signs that will tell you so.