The most common form of blog is a journal blog. They were the first blogs to hit the Internet a decade ago. Read this from Blogs- A Short History:
In the early days of the Internet, each new page was a cause for celebration. The early pioneers watched in excitement as the network grew, and they wanted to keep people informed about this growth. In 1992, Internet pioneer Tim Berners-Lee created the first What's New page; (or "diary blog") later, another pioneer, Marc Andreesen, put up a similar page. Each had hotlinks to the new pages springing up on the Net. As the Internet grew and the World Wide Web came about, other programmers created hand-coded pages with their recommendations for surfing the Net - they "filtered" the Net . Justin Hall started his filter log in 1994. In 1998, Jorn Barger coined the term "weblog." Soon, says weblogger and author Rebecca Blood, these "link-driven sites" were very popular, and webloggers became a community.
Each weblog included a list of similar filter sites. In 1999, websites Blogger and Pitas began to offer a simpler way to create a weblog. These hosted services allowed any person to easily sign up, create a blog, and write numerous postings. All without having to know HTML . Since then, millions of weblogs have been created. The term is now pronounced web-log or we-blog, or shortened to blog. And these blogs evolved into personal diaries or journals . Many journal-blogs still do include a list of other similar sites. This is a called a blogroll.
Read this condensed version of an article from Apophenia.
Before there were blogs the only sort of regularly-updated personal website out there was the journal. The journal was a personal account of the writer's life, generally very personal, and referring to daily/weekly events. Each entry tended to be a long journal 'page' and it tended to have at least some amount of thought put into it.
When the blog first came on the scene, it was a daily pile of links, with a bit of commentary. The links were to interesting news bits such as articles, photos, etc. and one blog would link to another blog. Soon, some of these 'bloggers' started writing more and more interesting content, and linking less. The other 'bloggers' liked what they say and would link to that interesting content, turning linkers into content providers.
These illustrates the difference, in some people's mind, between journal bloggers and bloggers in general. The journal blogger will have personal accounts as their primary focus whereas the blogger might need to write about a particular item of public consciousness. Of course there is overlapping and co-mingling of pure journal blogs and content driven blogs. So it could be said that blogs are written globally for a further reach and discussion of community driven topics and journal blogs are written for sharing personal insights and events.