Why are the terms SCSI 1, 2, and 3 so hard to understand?
What is SCSI-1, 2, and 3?
What is a good way to make sure I'm getting what I want?

Why are the terms SCSI 1, 2, and 3 so hard to understand?

The terms SCSI-1, SCSI-2, and SCSI-3 are commonly used to describe connectors, not standards. This is incorrect, but the whole industry does it, so here is a breakdown.

SCSI-1 :

1. DB-25
2. IDC 50
3. CX 50

SCSI-2:

1. HD-50
2. IDC 50

SCSI-3:

1. HD-68
2. MCX-80(SCA)

SCSI-5:

1. VHDCI-68 (.8mm) (Ultra)

What is SCSI-1, 2, and 3?

These are actually standards for SCSI devices. If you would like to know the exact definitions, then you can purchase the standards from ANSI. The ANSI SCSI standard is a multi-thousand page document with far more information than you need. Most likely, it will make SCSI even more confusing for you. See the next section for more information.

What is a good way to make sure I'm getting what I want?

There are alternate terms that let you know which interfaces your devices are using. I would recommend checking this link for exact info. I use this page as a reference, and it has never led me astray. http://www.scsita.org/terms/scsiterms.html