I have a 15" MacBook Pro mid-2010, running Sierra 10.12.1. I use Safari and Mail. Processor: 2.53 GHz Intel Core i5 Memory: 4 GB 1067 MHz DDR3 Graphics: Intel HD Graphics 288 MB Recently I've experienced more and more beach ball spinning, sluggish behavior (slow to open programs, windows, etc.), and lagging in typing when other apps are running. For instance, in typing an email, it takes a while to "catch up" with my typing. I've done a bit of web research, and ran the Disk Utility to check the system for errors. It told me I had errors, and needed to run the Repair using Command/R at startup, I believe. I backed everything up to my external hard drive using Time Machine last night, but I am a big chicken, and don't want to run into problems doing this repair. I've read things on various forums about partitions, drives, etc., and I am so confused. I am a basic user, and don't talk the talk like some know how to do, so excuse my basic questions: Is running the repair safe? Is there a chance it will wipe everything from my computer? If it were to wipe data, is running a restore from Time Machine difficult to do? Is anything going to happen during this repair that I need to be aware of? (prompts/choices?) Any advice is much appreciated!