SCSI 1 supports up to 8 devises including the SCSI card. The devices in a SCSI chain must have unique SCSI IDs. SCSI card typically have ID7. SCSI 2 is a more popular adapter and supports up to 16 devices, also has higher transfer speed. The SCSI chain must have terminators at both ends.
Terminators are resistors.
SCSI card usually has a built in terminator. SCSI hard drives are more expensive than EIDE hard drives but offer higher access speed. The first 1024Kb of ram represents DOS memory model. Memory above the first 1024K is called Extended memory. The first 64K of extended memory is called high memory.