SCSI FAQ of frequently asked questions and answers, includes information on LVD/MSE, HVD and SE. Also see our SCSI Glossary

SCSI FAQ Part 1

• Q. 1. What does the term "SCSI" mean?
• Q. 2. What is SCSI?
• Q. 3. What can I do with SCSI?
• Q. 4. I seem to remember hearing the term SASI in the past. What is it?
• Q. 5. Does SCSI work in both directions?
• Q. 6. What are the differences between SCSI-1 and SCSI-2?
• Q. 7. What are the differences between SCSI-2 and SCSI-3?
• Q. 8. What is the difference between single-ended and differential SCSI?
• Q. 9. What is meant by "narrow" SCSI?

• Q. 10. What is meant by "wide" SCSI?
• Q. 11. What is HVD SCSI?
• Q. 12. What is Wide Ultra SCSI?
• Q. 13. What is LVD SCSI?
• Q. 14. What is "multimode LVD" or LVD/MSE?
• Q. 15. What are the benefits of LVD SCSI?
• Q. 16. Is LVD SCSI backward compatible?
• Q. 17. What is Ultra160 or U160 SCSI?
• Q. 18. I have heard of U160/m SCSI. What is it?

• Q. 19. Is Ultra160 SCSI backward compatible?
• Q. 20. Is Ultra 160 SCSI better than fibre channel?
• Q. 21. Is Ultra 160 SCSI better than EIDE?
• Q. 22. What is Fast-20 [or Fast-40 or Fast-80] SCSI?
• Q. 23. Can I connect an Ultra 2 Wide (LVD) disk to an Ultra Wide adapter?
• Q. 24. What is Double Transition clocking?
• Q. 25. What is "Domain Validation"?
• Q. 26. What is CRC?

• Q. 27. I recently purchased a new SCSI drive with an SCA (or SCA-2) connector. How do I connect this to my cabled SCSI system?
• Q. 28. What is QAS?
• Q. 29. What is SCSI "packetization" (also called information units)?
• Q. 30. What are the five optional features of Ultra 160 (Ultra 3) SCSI?
• Q. 31. All the new drives have the LVD/MSE interface. Can I use them on a narrow single-ended SCSI bus?
• Q. 32. I know I can place a LVD/MSE peripheral on a single-ended bus, but the LVD interface is wide (34 pair cables) and the single-ended bus is narrow (25 pair cables). Any problems here?
• Q. 33. Can I attach narrow devices to a wide SCSI bus?
• Q. 34. I have heard the term "idc" applied to internal SCSI ribbon cables. What does it mean?
• Q. 35. Can I attach wide peripherals to a narrow SCSI bus?
• Q. 36. I note that in several of your FAQs you recommend the use of 68 pin to 50 pin adapters. Aren't they "impedance lumps" in the SCSI transmission line that can cause reflections and associated problems?

• Q. 37. I had a problem with my SCSI bus. It was much slower than I thought it should be. When I used a new SCSI cable that was six feet longer than the one it replaced, the system performance returned to what I think it should be. Why?
• Q. 38. How can I connect a HVD device to my single-ended bus? [or vice versa]
• Q. 39. How can I connect a HVD device to my LVD bus?
• Q. 40. I have a LVD/MSE bus with several multimode peripherals, and I want to add a single-ended peripheral to it. I know that LVD/MSE is backward compatible through the single-ended interface, but when I add the single-ended peripheral, the LVD peripherals really slow down. Help!
• Q. 41. How can I connect a LVD peripheral to my single-ended SCSI bus?
• Q. 42. Why does my LVD/MSE bus slow down when I connect even one single-ended peripheral?
• Q. 43. I connected what I believed to be a single-ended peripheral to my multimode (LVD/MSE) bus, thinking it would switch to the single-ended mode and operate, although at a slower speed. The bus simply shut down. What happened?
• Q. 44. How can I connect a LVD peripheral to an HVD SCSI bus?

• Q. 45. What are LUNs?
• Q. 46. Can I have more than one computer on my SCSI bus?
• Q. 47. What is the difference between SCSI and IDE (or EIDE or ATAPI)?
• Q. 48. Is SCSI or IDE better for me?
• Q. 49. Will my single-ended to differential converter also do differential to single-ended conversion?
• Q. 50. What is termination?
• Q. 51. SCSI requires terminators. Where should they be placed?
• Q. 52. What is the difference between passive and active terminators?
• Q. 53. Should I use passive or active terminators?