SCSI-1

SCSI-1 is what started it all. As you probably guessed, this standard is already obsolete. SCSI-1 basically involved the specs for the basic SCSI bus, which used an 8-bit bus, with about 5 MB/s max transfer rate. Data is transferred in parallel using multiple data lines. That's not really much, but you have to understand that back then, floppies were still in common use. It was very limited and only had the most basic features and transfer modes. The data transmission was very simple and used single ended transmission with passive termination. Single ended transmission or SE, involves sending positive and zero voltages to represent 1s and 0s. To understand what termination is, think back to high school physics class.

When you have a wave traveling along a piece of string, it will keep going until it reaches the end then reflect back but with a reduced amplitude. This is caused by interference between the reflected wave and the wave still traveling towards the end. Electrical signals behave in a similar way. So, when a data signal is sent along a SCSI bus and it reaches one end of it, the reflected signal will cause interference with other data signals on the bus. To eliminate this the signals are effectively terminated once they reach the end of the bus. Passive termination uses simple resistors to do this. It's not really used for any modern SCSI speeds.