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.
Record A is appended to the log, but the log is not forced. The ILog implementation copies the record to a buffer in memory and returns a success code. Record B is appended to the log, and the ILog implementation decides to force the log to disk. This is either because the caller asked the log to be forced or because the memory buffer is full. However, the write operation fails, for example because of low disk space.