While the computer is running, the RAM contains OS data, running programs, as well as input, output and intermediate data processed by the processor. If there are problems with RAM, everything will work badly.
MemTest86 is a free program that allows you to check the RAM of a computer or laptop for errors and problems in operation. The peculiarity of the utility is that it does not run in the operating system, but in the form of a separate image, which must be written to a USB flash drive and run from the BIOS.
This method of launching has its advantages: the program can test all the RAM, and the operating system will not interfere with it. If the operating system does not start or fails, then you can find out if everything is fine with memory.
The program first writes the entire memory with repetitions of the prepared data block, then reads and compares what is written with what is read in two passes: starting from the lowest addresses to the highest and vice versa. The procedure is repeated for many different data samples to identify all possible errors.
It is best if you check the memory one module at a time. That is, we open the computer, extract all the RAM modules except one, and check it. After the end, the next one and so on. This way it will be possible to accurately identify the faulty module.