I've considered ram an extremely important entity for many years (it's often underestimated.) Many computers are sold with just a minimum amount of ram. Yes iMacs can have more ram added to them (mac techs [/should I say salespeople] often don't tell you that.) (I was lucky when I bought my g4 b/c the same store was offering a special discount for ram at less than half the price than everywhere else - too much of a temptation to fill its stomach full!) Yes external HDD's can become corrupted / infected with virus, but in my experience, cd's can be affected with both things also & I've also had corrupted/poorly reading dvd's. I love dvd-rw's! But for me personally, for my particular needs, they're lacking just a touch. Plus it's slow to copy back to the comp. But I'm at the high-end of needs. For the average user, dvd's are more than satisfactory!!! Even those who dwn'd massive amounts! I have a massive amount of cd-rw's I rarely use nowadays b/c it doesn't suit me for video backup. Video is at the very high-end of needs for backup, rendering, ram, cpu, graphics card, etc. But for everybody else, I'd suggest dvd burners are multi-functional whereas an ext.HDD has only 1 purpose.