Adaptec Nodem

Personal Computer Local Networks Report 5th Ed., Sep 1991 (pages 65-70)


Adaptec is a leading supplier of high-performance input/output solutions. 1/O is a critical function of every microcomputer, allowing data to be transferred between a computer and its peripherals. Adaptec products include proprietary VLSI circuits, a broad line of personal computer- and SCSI-based controller and host adapter boards, and a family of SCSI test and development systems. These products are designed for a variety of applications, from single-user computer systems to network file servers. Adaptec also supplies integrated circuits to peripheral manufacturers for use in intelligent, high-performance peripherals.

It is Adaptec's belief that today's workplace is thirsty for connectivity. While a variety of networking products exists, Adaptec says there are conspicuous paps in the “universe” of microcomputer connections. To help meet this need, Adaptec has introduced Nodem, a LAN interface unit said to take full advantage of the device-independent Small Computer System Interface (SCSI). Nodem is a small, external box that will connect SCSI based microcomputers and peripherals to any
Ethernet network without the need for an internal card in the micro. Adaptec designed Nodem as an inexpensive networking solution whose modularity enables it to be easily adapted for various systems and functions. In most cases, Nodem hardware remains the same; only software changes.

Initially, Adaptec is offering Nodem with a system diskette for Macintosh computers that use SCSI] (the Plus, SE, Il, and future Macintosh computers), Adaptec boasts that its Nodem is the only low-cost networking product that links all these popular Apple Computer machines via high-speed Ethernet without taking up a valuable expansion slot. (This is important, since the Macintosh Plus has no extra slots and the Macintosh SE has just one.) With Nodem, all AppleTalk applications can run unmodified, but the raw data communication rate is 40 times faster than on LocalTalk. Nodem connects Macintosh computers to Ethernet through the machine's SCSI port.

In the near future, Adaptec will introduce IBM PC and PS/2 system diskettes for Nodem that will allow existing hardware to be used with IBM PCs and compatibles. Since Nodem is inexpensive and needs no slot for computers with an SCSI port, it will also provide tomorrow's SCSI laptop computer with a simple method of LAN connectivity.

Networking through SCSI is a new concept. Nodem is a logical outgrowth of Adaptec's SCSI product line and taps its expertise in improving high-speed serial I/O, whether the product is a drive controller or a LAN interface unit.

Until now, Ethernet products have relied on costly chip sets made by a few leading IC manufacturers. However, Adaptec took a different approach for Nodem by using several of its own high-volume, low-cost SCSI drive controller and protocol chips to implement Ethernet, expenses were lowered. By connecting through an SCSI port, Nodem also saves an expansion slot and simplifies installation.

To support its entry into the networking market, Adaptec has assembled a team of LAN experts headed by Phil Belanger, well known in the industry as the father of Omninet, a pioneer network for personal computers. Belanger has spent 10 years in product development and management, designing a wide range of protocols and networking products.

The Role Of SCSI

SCSI was invented by Adaptec's founders as a standard I/O interface that would allow the connection of different devices. The only intelligent I/O interface, SCSI actually functions like a host bus, offloading tasks normally performed by the CPU and thereby increasing performance. SCSI makes a system more flexible, because it can be expanded and changed without affecting existing device driver software or interface hardware. The intelligence of the interface masks the nature of peripherals from the host system, supporting truce mix-and-match peripheral subsystems and simplifying system and upgrades. In this way, time-to-market is also reduced.

By summer of 1987, there were almost 500 SCSI products being sold by 167 manufacturers, and about 30% of the small magnetic disk drives now being shipped use SCSI. All major OEM suppliers have at least one SCSI product offering. According to research firm Dataquest, SCSI will dominate the market, being used on 55% of small disk drives by 1992.

Presently, the Macintosh is the primary micro employing SCSI. Later-model Macintosh computers are equipped with an SCSI port (SCSI upgrade kits are available for earlier machines), which has encouraged the development of many SCSI peripherals. However, an increasing number of peripheral manufacturers outside the Macintosh market are also choosing SCSI because of its performance and ease of integration, as well as the fact it shortens development lime.

While IBM has not yet included SCSI on its microcomputers, it has said it will introduce an SCSI drive. This statement of direction could be a confirmation of IBM's imminent migration to intelligent 14 on its micros — which means SCSI. Some IBM compatibles — such as those from Tandy Corporation — already implement SCSI.

SCSI is a widely accepted interface for connecting peripherals, such as hard disk and tape drives. But using SCSI is also a simple solution for connecting a device to a network, because it treats the LAN as another peripheral. In addition, SCSI's multitasking capabilities make it well-suited to networking applications.

Adaptec's founders originally built into SCSI a set of commands for communication devices that are only now being utilized in Nodem. SCSI features like disconnect/reselect and the target/initiator capability have been included in Nodem to facilitate the smooth, fast flow of information to and from the host machine.

Since SCSI, in a sense, allows computers and peripherals to speak a common language, it potentially solves the biggest problem in LANs today: communication between unlike devices, Through SCSI's large initiator mode, Nodem allows simple, low-cost, peer-lo-peer communication. In designing Nodem, Adaptec's goal was to exploit the “universal” nature of SCSI by employing the Common Command Set, as well as to provide upward compatibility with SCSI II. One of the benefits of SCSI II is accommodation of either fast synchronous of asynchronous communications.

The Nodem Product

Highly modular, Nodem is designed for flexibility by being easy to configure for various host environments and Ethernet media. (The design of Nodem is such that other types of media could be accommodated with minimal alterations.) Basic Nodem hardware consists of the interface unit, a modem-sized box that can stand upright and is equipped with a snap-in media card for standard Ethernet, thin Ethernet (Cheapernet), or twisted-pair Ethernet. (Adaptec has licensed its twisted-pair implementation from Synoptics.) Nodem comes with its own wall-mounted power supply.

From this flexible hardware base, Nodem can be adapted through software on system diskettes for a variety of environments and applications. For example, the system diskette now being offered for Macintosh machines will be supplemented later by IBM versions (for IBM PC and PS/2 microcomputers and compatibles) that use the same hardware as that for the Macintosh. At that time, Adaptec feels it will have an industry first: a single, low-cost, external hardware product that connects IBM and Macintosh micros to Ethernet.

Nodem can be easily installed by users. An SCSI cable on the host end and an Ethernet cable on the network end are plugged into Nodem. The system diskette can be copied onto a hard disk, automatically loading each time the host system is turned on. Adaptec will introduce additional LAN products based on the Nodem hardware architecture in the future (See "Other Nodem Networking Products” section below).

Nodem For The Macintosh - The Macintosh version of Nodem replaces the physical (called LocalTalk) and data link layers of the AppleTalk protocol architecture. This means that all AppleTalk applications — such as AppleShare and TOPS-will run unmodified through Nodem, whose presence is transparent to the user, Besides giving Macintosh LANs the speed and network size of Ethernet, Nodem is inexpensive enough to make it practical for every Macintosh in a network.

Nodem-attached Macintosh computers can perform Macintosh-to-Macintosh communication functions as well as communicating with other systems (including IBM, DEC, and Sun) through Ethernet. This capability is becoming increasingly important as the use of Macintosh computers grows in business, where sharing information with other systems is often needed. The increasing complexity of AppleTalk applications and the enlargement of Macintosh workgroups are other factors indicating the need for Ethernet.

Ethernet operates at a fast 10 Mbps compared to 230 Kbps for LocalTalk. This Apple LAN product links a maximum of only 32 Macintosh computers, while 254 AppleTalk nodes can be connected via Ethernet. In fact, the practical number of Macintosh computers that can be added to LocalTalk is significantly lower, because performance increasingly degrades as the user population grows.

Given the fact that close to one million AppleTalk nodes are now installed, Nodem makes possible a pragmatic solution: users can gel the speed of Ethernet while retaining all their existing application software.

Nodem For IBM Microcomputers - Many LAN options exist for IBM microcomputers. IBM has offered networking products employing broadband and token ring, with Ethernet products also available from third-party vendors. However, Nodem is said to be the first interchangeable Ethernet product for both IBM and Macintosh microcomputers. By supporting NETBIOS (the most widely utilized standard interface in the DOS environment), Nodem for the IBM will offer application software compatibility with the large installed base of PC networking software.

Nodem will also support OS/2. As a true multitasking operating system, O5/2 and its LAN Manager will simplify the development of distributed applications, which should increasingly appear in the near future. Adaptec has plans to introduce additional Nodem software supporting LAN Manager and OS/2 networking applications.

OS/2 and SCSI are an appropriate match when it comes to connectivity. As a multitasking interface, SCSI will utilize the power of OS/2. Another advantage of SCSI could have a more global effect: in the scramble to keep up with the new marketplace that is being created by the PS/2 with its Micro Channel, vendors will want lo speed up development — and the flexibility made possible with SCSI would help this become the interface of choice for many of tomorrow's 32-bit microcomputers and peripherals, increasing the market for SCSI LAN products such as Nodem.

Even DOS and OS/2 micros without SCSI can benefit from Adaptec's next product in the Nodem family. The company offers a line of host adapters that allows the attachment of SCSI peripherals (including Nodem) to computers without an SCSI port on the system board. Adaptec supplies host adapters for the PC AT and PS/2 microcomputers.

Other Nodem Networking Products

The flexibility of the Nodem hardware architecture can be applied to solving other connectivity problems. For example, attaching a shared peripheral to a LAN now requires a file server, which is a computer used as a dedicated storage system or peripheral control device. Contrary to the distributed nature of networks, this scheme only creates a bottleneck as data and peripheral commands funnel through a single point — a costly file server.

A better solution is direct attachment of peripherals to the network while file servers are used for the task they perform best: information storage. Unfortunately, there is currently no product that makes this solution possible.

However, Adaptec is now working with peripherals manufacturers to develop intelligent network front ends (basically, a Nodem and appropriate software) that allow direct attachment of SCSI peripherals to Ethernet. Nodem will be configured as a low-cost LAN adapter that eliminates the need for file servers to attach peripherals, running the software for the network protocols, and accessing the peripheral as an SCSI initiator. Particularly with today's new class of high-end peripherals like laser printers, scanners, optical disks, and CD/ROM devices — all of which have SCSI interfaces—-the Nodem concept will make these peripherals very cost-effective shared resources.

This simple way of connecting peripherals is made possible by SCSI, whose unique target/initiator mode enables Nodem to act as a sender or receiver of commands and information between diverse equipment. Also, Nodem can be configured for other economical networking functions as well: e.g., Nodem can connect up to eight LANs using simple hardware al a very low cost, and it can also be used as an affordable gateway, connecting networks that use different protocols.

Nodem System Components, Specifications

A sample Nodem system configuration is depicted in Figure 1. Nodem specifications are listed below.

Figure 1: Sample Node m System Configuration

Nodem Specifications


  • Dimensions
    • 8.4" x 5.3" x 22"
    • 213 mm x 135 mm x 55 mm
  • Dual board architecture
    • Main system board
    • Media Card
  • Multistate LEDs
    • Power-on (yellow), Ready (green), Error (red)
    • Network active
    • SCSI active


  • Separate wall-mounted power supply/transformer (can be replaced for international requirements)
  • Nodem Input Power
    • 16 V AC @ 2 A, 40 W, 47-400 Hz

Processor Memory

  • Intel 12 MHz 8051 CPU
  • 32KB RAM for downloadable Nodem system firmware
  • Standard buffer RAM
    • 8 KB transmit
    • 32 KB receive
  • Optional 16K firmware EPROM slot for on-board Nodem system firmware (for connection of disketteless devices)

Ethernet Interface

  • Standard IEEE 802.3 Ethernet implementation
  • 10 Mbit/second data rate
  • Snap-in Media Cards
    • Thin Ethernet with on-board media access unit (MAU) BNC connector
    • SynOptics Ethernet over TP with on-board MAU and RJ-45 connector
    • (Thick) Ethernet with AUT to external transceiver and DB-15 connector

SCSI Interface

  • Synchronous/asynchronous support
    • Synchronous burst rates up to 5 MB/s
    • Asynchronous burst rates up to 2 MB/s
  • Dual, standard 50-pin SCSI connectors
    • Nodem can share SCSI bus with up to 7 (including host PC) other SCSI devices
    • Modem can reside anywhere on SCSI daisy chain
  • Externally accessible SCSI address switch
  • External SCSI power circuit breaker
  • Current SCSI implementation expandable to support:
    • Multitasking, multithreading
    • Target and initiator modes
    • SCSI 2 commands
  • SCSI system cable or extension cable required. SCSI terminator may be required


System diskettes include:

  • Downloadable (to RAM) Nodem system software and firmware - ensuring simple upgrades
  • Network operating system drivers


By supporting Macintosh and IBM microcomputers, Nodem should be assured of a large marketshare in the coming years. While IBM is well-established in the business world, Macintosh is also becoming a popular business computer. According to Dataquest, almost 70% of the Macintosh computers sold last year were used in business applications. Apple has been increasingly successful in penetrating the larger business accounts that have been IBM's stronghold in the past.

While the largest market for LAN products is the business sector, the higher-education market is another opportunity for Nodem. Macintosh computers are widely used in this market, although IBM is working actively to increase its base. Ethernet has long been the connection method of choice, since it can link the variety of equipment usually found in this environment.

Adaptec will market Nodem through VARs of networking products, large computer dealers, and OEMs. The company will launch joint development efforts, where appropriate, to create software and hardware that will allow Nodem to be configured for a variety of functions.

Adaptec firmly believes that Nodem will carve a place for itself in a market seeking affordable, flexible, high-performance methods of connectivity.

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