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SCSI Ethernet

Introduction

In the dawn of PS/2 history, a number of manufacturers developed external SCSI to Ethernet converters, or "SCSI Modems". Unfortunately, there were no PS/2 SCSI to Ethernet devices. The available 10 Mbit ethernet adapters kept up with things until AFTER the PS/2s were no longer made (1996-ish).

These SCSI to Ethernet devices made sense in the Mac world, due to limited slots AND the availability of SCSI, either cards or system boards. LocalTalk was part of the Mac system, but it was limited (how so, I'm not a Mac Fanboy). -LFO

Articles

Are You Ready For Ethernet? MacUser Vol. 6, No. 6, Jun 1990
   HTML version (selected parts only)
Networks That Sing MacWorld Sep 1988
   HTML version (selected parts only)
Instant Ethernet: 10BASE-T MacUser Vol. 7 No. 9, Sep 1991
Personal Computer Local Networks Report 5th Ed., Sep 1991 (pages 65-70)
   HTML version of Adaptec Nodem

SCSI Ethernet Products

• NODEM invented by Adaptec @1988, sold to LRU Systems @1993.
• Ether+ by Compatible Systems
• NuvoLink SC by NuvoTech, but actually made by Compatible Systems
• FastNet SCSI by Dove Computer Corporation

Are You Ready For Ethernet?

Source: Are You Ready For Ethernet? MacUser Vol. 6, No. 6, Jun 1990

A SCSI Ethernet device must share the SCSI bus with other devices such as hard-disk drives. Because the Mac's SCSI bus is slower than either the NuBus or PDS and because SCSI gives priority to disk access commands, SCSI Ethernet performance pays a penalty. This slowdown is especially noticeable with file transfers in which the hard-disk drive is being heavily worked at the same time as the Ethernet interface. If you're after brute performance, our tests show that SCSI adapters are not your best choice (see Figure 2 in the original article).

But don't dismiss SCSI adapters entirely, They're conveniently transportable among machines and easy to install. All four SCSI adapters have easily accessible switches for setting the SCSI identification number. The Adaptec Nodem is the most versatile, with two 50-pin SCSI ports and an external terminator plug that lets you place the Nodem anywhere on the SCSI chain.

The Compatible Systems Ether+ and Nuvotech NuvoLink SC arc internally terminated and have just one 25-pin SCSI port, so you must place them at the end of the chain — a real problem if you already have an internally terminated SCSI device. That the Ether+ and NuvoLink SC should share these and other features is not surprising, because Compatible Systems manufactures the hardware contained in both. The internally terminated Dove FastNet SCSI has one of the most unusual SCSI connection schemes we've ever seen: An 18-inch cable sticks out of the back, with a 25-pin plug on the end to connect to the Mac. A 25-pin port receives a SCSI cable from the next device in the chain.

Dove's FastNet SCSI is a unique device. It contains its own CPU, intended to lighten the Mac's network-processing load. Unfortunately, no AppleTalk software currently exists to take advantage of the FastNet SCSI, and it performed poorly in all our tests. We look forward to learning whether the on-board CPU can make a difference if performance-enhancing software is ever developed for it.

Networks That Sing

Source: Networks That Sing MacWorld Sep 1988

Many of the estimated nearly one million LocalTalk users have run into this popular network's major limitations: a maximum of 32 nodes on a network and greatly degraded performance when even as few as 16 users are online. Until now, it's been expensive to get to the solution — Ethernet — which easily handles 254 nodes at 40 times the data transfer rate of LocalTalk (Ethernet is so fast, a file server can perform like a resident hard disk).

Now Adaptec is offering Nodem, which it claims is the first cost-effective Ethernet connection for all SCSI-capable MS-DOS computers and Macs (all Macs except the 128K and 512K have SCSI ports). Nodem is a 2-inch-thick, modem-size box that's external to any computer — meaning that it doesn't take up an internal slot.

Nodem connects a computer's SCSI port to Ethernet's standard coaxial, or twisted pair, cabling. When you turn on the computer, Nodem's software automatically configures the computer for transparent communications using AppleTalk, NETBIOS, and OS/2 protocols — there's no need to modify any application software or any procedures.

The implications? Not only could Nodem overcome many of LocalTalk's limitations, it could provide Apple with the low-cost connectivity capability it needs to become fully integrated into business, industry, and education. It could also offer the opening that developers need to introduce the next generation of productivity software software focused not on individual users, but on groups sharing and exchanging resources and information.

An increasing number of IBM-compatible computers have SCSI interfaces. For those that don't, Adaptec provides host adapters. Nodem for the Mac is expected to be available in September for $545 for standard Ethernet cabling, or for $595 for Ethernet twisted-pair or Cheapernet. IBM versions are projected to be available in the first quarter of 1989. (Other Ethernet connection devices range in price from $699 to $1250 and are produced by Apple, Dove Computer, Kinetics, AST Research, and 3Com.)