by Wayne M. Krakau - Chicago Computer Guide, July 1993

It's pronounced "Scuzzy Too", written "SCSI-II", and means Small Computer Systems Interface, Version Two. It was designed as the successor to the original SCSI standard to be a common connection method for many different computer peripherals.

These peripherals include: hard disk drives; removable cartridge disk drives, read-write, WORM (Write Once-Read Many or Mostly), and CD-ROM (Compact Disc Read-Only Memory) optical disk drives; scanners; and even printers.

Though the SCSI circuit board placed inside the PC is usually called a controller, it really is a host bus adapter (HBA). The controlling circuitry is normally inside of or attached to each peripheral. The HBA just provides a means for the SCSI devices to communicate with the rest of the computer system.

Each HBA can handle up to seven peripherals, daisy-chained from each one's output port (connector) to the next one's input port with each port arbitrarily designated as input or output. On each end of the bus (the chain of devices) a terminating resistor (the original Terminator) is required. The HBA is equipped with ports to accommodate both internal and external devices.

The SCSI II standard was written to allow dissimilar devices from different (and often competing) manufacturers to coexist happily without unduly complicating the setup of the total computer system. That's the theory. Try to implement it, however, and reality smacks you in the face.

First, there are multiple types of HBAs. There are 8-bit HBAs, for XT class machines that also can be used in ISA (AT-class, known formally as Industry Standard Architecture) machines for low-performance applications such as with slower CD-ROM drives. There are standard 16-bit ISA HBAs. There are pseudo-busmastering 16-bit ISA HBAs for higher performance. Both also can be used in EISA (Extended Industry Standard Architecture) machines though the use of the pseudo-busmastering type will force a restriction to 16MB (megabytes) of random-access memory in the computer.

Then there are the specialty HBAs. These include EISA and Microchannel (IBM's proprietary bus structure used in some of their PS/2 machines) computers. Here are even more choices. While both busses have a 32-bit interface, not all cards with a 32-bit physical interface fully utilize it. (This warning holds true for other EISA and Microchannel boards, not just SCSI HBAs.) They may have only 16-bit internal circuitry. Remember, most computer performance calculations are based on the weakest link principle - one low-performance part (the 16-bit portion) working in conjunction with high performance parts (the 32-bit physical connector) effectively restricts overall performance of the system to its own limits. Occasionally the same effect is also seen with 16-bit boards (both SCSI and others) that contain chips that can only handle eight bits of information. VGA cards and sound boards have historically been notorious for this trick.

For these specialty busses, one other issue appears - busmastering. Both EISA and Microchannel allow for several true busmasters, as opposed to the single pseudo-busmaster (also called a DMA or Direct Memory Addressing busmaster) supported by ISA machines. Some boards for these machines (again including both SCSI and others) are not busmastering, thereby lacking the characteristics needed to take full advantage of the performance enhancing features of the specialty busses.

Besides the previously mentioned generic (my own term for being usable for theoretically any brand or type of SCSI device) SCSI HBAs there are many variations on the SCSI theme. There are still devices (HBAs and peripherals) available that follow the original SCSI standard, or to make matters even more confusing many that only partially support SCSI-II! Luckily, SCSI-II was designed to accept the older standard and the hybrids, but comparing performance can be ridiculously convoluted.

And now for the really fun part - proprietary and limited SCSI HBAs. Sound boards with built-in SCSI, scanners, older removable cartridge drives, and CD-ROM drives bundled with HBAs are all notorious for having half-baked SCSI implementations, often without making their limitations apparent. Many of them only handle their own devices. Some of them only work with a limited selection of peripherals. Most have non-standard software so they cannot be easily updated to support new devices.

Once you are past the basic hardware issues involved in installing a SCSI-II HBA, the software games begin. If you have a SCSI-II HBA and a SCSI-II peripheral, you cannot necessarily get them to communicate. Corel has some interesting driver software that alleges to work with almost anything within DOS or Netware, but I really don't care for its Netware version. Micro Design International's SCSI Express is the best I've seen in a Netware environment and does fairly well in a DOS environment. Adaptec's ASPI software has become the major defacto standard for everyday use, but their recent modification that keeps their software from working with any non-Adaptec HBA may kill their inertia. Their software now stops dead in its tracks and complains about a "foreign adapter" if it sees other manufacturers' cards. This xenophobic attitude is not going to do much for Adaptec's public image.

This list of the potential hazards of SCSI is not meant to dissuade you from purchasing SCSI. SCSI is the best way to go for file servers or for individual computers needing optical drives or scanners. It's just to warn you to be careful.

As I write this, I am in the process of completing the integration of a single-user document and image management system using a SCSI-II HBA to access a 1GB (a gigabyte is 1024 megabytes) internal hard disk, an external 650MB multifunction (using both read/write and worm cartridges) optical drive, a 2GB internal tape drive, and a ten page per minute scanner.

This nightmare project has been plagued with a combination of factually incorrect documentation, ambiguous documentation, physically unreadable documentation, missing documentation, mismarked jumpers (on the circuit board), memory management conflicts, disk-compression utility problems, cache problems, print spooler problems, keyboard accelerator conflicts, video accelerator problems, bad advice from multiple technical support personnel, factually incorrect advice from multiple support personnel, multiple occurrences of SCSI driver software problems, and, finally, an unusual applications software bug that has been unreproduceable elsewhere. This integration time was non-billable.

All this after checking with all the manufacturers involved to get their confirmation the proposed system would work. Their answer was uniformly - "No problem" - riiiiiiiight. Systems integration is not always fun.


As a follow-up to my comments on the upcoming merger of NOMBDA, the National Office Machine Dealers Association, and LANDA, the Local Area Network Dealers Association (now awkwardly referred to as NOMBDA/LANDA), I found the following quote in a NOMBDA publication as part of an article promoting the merger:

"...and this merger of NOMBDA's copier industry expertise with the LANDA networking know-how represents a cross-pollination of dealers, customers, and vendors that will surely lead to the long term growth of both industries."

I think I can remember overhearing a conversation amongst other dedicated LAN resellers in which they were commiserating on how unsuccessful their businesses were due to their lack of in-house copier technology expertise. Hmmmm. I guess I must have wasted the last ten years working with LANs and spending many thousands of dollars and hundreds of hours on LAN classes while I was falling behind in that critical high-tech copier stuff. I wonder if there is a CCE (Certified Copier Engineer) rating that I could study for?

                                       1993, Wayne M. Krakau