Differences between SSDI & SSI-
[The main difference between Social Security Disability (SSD, or SSDI) and Supplemental Security Income (SSI) is the fact that SSD is available to workers who have accumulated a sufficient number of work credits, while SSI disability benefits are available to low-income individuals who have either never worked or who haven't earned enough work credits to qualify for SSD. ]
http://www.disabilitysecrets.com/page5-13.html

If you are considering an SSDI claim, I really suggest exploring the useful stickies on our SSDI forum page before hand and to make sure you qualify-
http://neurotalk.psychcentral.com/forum28.html
Don't start your claim unprepared!!-
http://neurotalk.psychcentral.com/thread148967.html