College admissions.
There isn't a conversion between the two. The SAT I is the standard math, reading, writing test, which is required for most colleges. The SAT II, know as SAT Subject Tests, are one hour tests in one subject only. These tests allow you to show your strengths in particular subjects - especially the sciences and foreign languages as these are not tested on the SAT I - but most students take them because some colleges require them. SAT II scores have varying curves depending on the test, so conversion to SAT I scores is impossible.
Your SAT scores come in about 3-4 weeks after your test date.
I'm guessing that 900 is a combination of two of the scores because the highest you can get on one of the SAT section is 800 So getting 900 is NOT good.
ACT: SAT
You can choose which test scores you want to send. You are required to send one of the two tests.
Colleges may take up to two weeks to receive the test scores. Although the sending of scores is done electronically, it takes a surprisingly long amount of time for CollegeBoard to actually send out your scores, depending on the amount of requests.
Your SAT score is out of 2400. Each section is scored out of 800 points. SAT Essays are graded by two essay-graders on a scale from 1 to 6. The two scores are added together to give you your essays core. The essay score is out of 12 and is factored into your writing score.
I'm not sure who 'they" is in your question, but most colleges consider all three parts of your SAT score. However, colleges often place more significance on your scores on the math and critical reading parts of the SAT, as those parts of the SAT have been in existence for decades, whereas the writing part is new. If you see an SAT score on which only two parts of the SAT have been reported, it is almost always the math and critical reading parts.
Many highly selective schools require that you take at least one or two SAT II tests in order to look at your scores in specific areas. If you are looking at colleges that require these tests, you should take them. They are shorter than the normal SAT, and you can choose which subjects you want to take. For example, I took Math II, Chemistry, and Biology - E. But there are many different tests, including two levels of math, two biology tests, modern Hebrew, languages, etc. You can take one, two, or three in a given day. I would recommend taking three tests and then sending the scores for your best two. It only takes a morning and can boost your college admittance chances.
"A minimum score of 1540 on the new SAT I exam or 23 on the ACT (writing scores are required by OSU); AND an average of 470 or above and a minimum total of 940 on two SAT II Subject Tests:(Math Level I or IIC is required) plus a second test of the students choice."
how are rulers used
I have been looking for the same definition myself (and I cannot find it on collegeboard.org). The answer isn't as obvious as it seems. It appears to be the verbal and math scores, and does not include the writing. I only found this in writing one place, an article in the DailyAdvance.com, but it confirmed my suspicions about using only the two scores when looking at merit scholarship requirements. I recommend, however, if you are submitting scores for a scholarship or a college application, to check with the organization as to exactly what they want.