In the past most people were not familiar with computer world, but now it is one of the causes of the improvement in our quality of life. Most of the people were not so familiar with computer working in the past, yet nowadays many and more people are becoming more knowledgeable about computer working which is one of the leading causes to improve our life quality.

Well, the part you inquired about is correct. However, there is an ambiguity regarding the pronoun 'it' in ' ... now it is one of the causes ...". What is one of the causes? Familiarity with computer world, computer world, or computer?

In the first sentence you left the "s" out of "computers." It should be "computers, not "computer." The second sentence is missing the "the" in "the computer world." And I would not say "causes of improvement" but "reasons for " instead. "Causes of" just sounds odd to me.

Hi Yes both correct. However the first sounds a little more general and the second sounds more specific if followed up by a statistic or figure. I'd say you can use either for an essay, but if you have some statistics to back up this statement use the second option.