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For the Commodore 64 & 128 Computers

Written by eBay's 94Bravo

(Latest revision: 7.3; January 2008)

More downloads, more info and an updated section on the multiplexer unit, including schematic, timing diagram and detailed troubleshooting procedure.  Also see the host adapter installation page regarding use of a Swiftlink or Turbo232 EIA-232 serial interface cartridge with the Lt. Kernal.  For those who asked about 1 gigabyte storage capacity, please re-read the new "Wall" page.  Also, see corrections to C64C installation.
Coming Soon - C128 Daughter-Board.

NEW!  Steggy, one of the original software designers and contributors to the Lt. Kernal system, has written a new Multiuser Database Programming article.  The articles explores ISAM-like database management that can be implemented on the Lt. Kernal with user-written code. I am very pleased to present these ISAM Articles and Steggy's continuing Updates.




Hard Drives





Editing SYSGEN




SCSI Adapter


Multiplexer Unit


Drive Case & Cables

Complete Manual

The Wall

DOS Commands

This website is an archive of information about the Xetec Lt. Kernal SCSI hard drive subsystem for the Commodore 64 and 128 computers.  I have tried to put together a definitive knowledge base that covers the use, maintenance, repair and upgrade of the Lt. Kernal.  All information is available in the public domain, has been provided by Lt. Kernal experts (including Steggy & Pete Bergeron) or has been derived from my personal experience using the Lt. Kernal since 1987.  This site is regularly updated, so I invite technical additions, corrections or any other information that will improve content.

Back in the late 1980's, many of us ran a BBS, repaired systems and helped others with their Lt. Kernals.  Others developed Lt. Kernal software for business use.  There were numerous resources for LTK information, where it was possible to exchange ideas, download files, and share equipment problems and solutions.  The best of these were the BBSes maintained by Fiscal Information and Xetec, Inc., the companies that developed, marketed and supported the system.

Upon discontinuing the Lt. Kernal product line in December 1991, Fiscal shut down their BBS, and shortly before Xetec ceased doing business in 1995, their BBS went down as well.  Soon, other Lt. Kernal resources disappeared, leaving a huge void for those wanting to continue to use their systems.

Following Xetec's close, the only resource for hardware and technical support was Ron Fick, who acquired Xetec's remaining parts inventory and single-handedly supported the Lt. Kernal until his untimely death in December 1999.  Unfortunately, with Ron's passing, no one that I know of has continued his good work.

Therefore, I have created this site in hopes of providing all the data you need to use and maintain the Lt. Kernal.  This site also includes information needed to upgrade your system, including a new section on the multiplexer unitcomplete with schematic, timing diagram and detailed troubleshooting procedures.

Lt. Kernal Host Adapters and Enclosure

Xetec Lt. Kernal subsystem, with both host adapter types.

System Description

What is the Lt. Kernal (LTK) subsystem?  And, how did it get its strange name?

The Lt. Kernal is an integration of SCSI (Small Computer System Interface) electronics, Winchester fixed disk storage technology, and a professional-grade disk operating system (DOS).  SCSI provides an intelligent, high speed parallel data bus between computer and hard drive, and the DOS gives the computer the capabilities needed to effectively manage and utilize the drive's capacious storage.  The result is a Commdore 64 or 128 on steroids, a system that appears to be an eight bit microcomputer but embodies the personality and features of a high-powered minicomputer.

Prototyped in 1984 and released for production in early 1985, the Lt. Kernal revolutionized the concept of mass storage for eight bit Commodore machines and set the standard by which later such systems would be measured.  The C-64 version of the Lt. Kernal was up to 100 times faster than the Commodore 1541 floppy drive, and the C-128 version running in FAST mode was about 170 times faster.  The Lt. Kernal DOS introduced many new features to the system, such as the ability to execute a program by typing its name and pressing the Return key.

As is characteristic of any system that implements SCSI-controlled mass storage, the Lt. Kernal hardware consists of two major components: the hard drive itself, mounted in an external, self-powered enclosure, and a host adapter that plugs into and is powered by the computer's expansion port (see the photo at the top of this page).  The host adapter and hard drive assembly are interconnected by a data cable, which is what embodies the SCSI bus.  An accessory device called a multiplexer may be used to gang multiple computersin any combinationto a single hard drive unit, giving each machine transparent access.  Advanced programming techniques can make a multiplexed system behave much like a multiuser minicomputer, resulting in a remarkably powerful shared data storage and retrieval system.  Since the Lt. Kernal is designed around SCSI, multiple hard drives may be attached to the system, allowing a maximum aggregate storage capacity of approximately 330 megabytes.

Almost all of the Lt. Kernal magic occurs in the host adapter, which "adapts" the internal address and data bus hardware circuits of the Commodore computer (the "host") to the SCSI bus in a way that is invisible to the rest of the system.  As no eight bit Commodore computer has ever had a built-in DOS, let alone one suitable for use with a high capacity SCSI hard drive, the host adapter includes 16 kilobytes of RAM to provide space in which to execute a sophisticated and powerful DOS that acts as an extension to the standard Commodore kernal operating system.  Complex electronic logic in the host adapter maps the DOS in and out of processor address space according to the operation being performed, resulting in a high degree of compatibility with the standard Commodore kernal and memory map.

As for the Lt. Kernal name, it was coined early in the product's development as a pun on the way in which the prototype operated.  In order for the Lt. Kernal's DOS to function on the C-64, it had to be linked into the kernal.  In the prototype, this was accomplished by running the DOS in the $E000 block of RAM underneath the kernal ROM.  Due to the architecture of the C-64, getting the Lt. Kernal's DOS to run at all was a major programming feat.  It was, in fact, more than major, but still beneath the kernal.  Hmm...more than a major but below a  That meant the DOS was actually a Lt.  Arrgghhh!!!  However, Commodore had misspelled "kernel" and thus the system was christened Lt. Kernal.  Production units moved the DOS into RAM inside the host adapter, but the name stuck.

In the late 1980s, several competitors to the Lt. Kernal were developed, most notably the line of hard drives produced by Creative Micro Designs (CMD).  However, none of these systems has ever approached the performance and sophistication of the Lt. Kernal design, and the Lt. Kernal continues to be the apex of eight bit Commodore-compatible hard drive subsystems.

If your primary use of a computer is for productivity, you should consider a Macintosh or a PC running Linux.  However, if you are interested in experimenting with eight bit Commodore hardware, the Lt. Kernal subsystem is an ideal development and testing platform.  To get the most from your Lt. Kernal, this is the site for you!

Each of the other sections of this website cover the entire spectrum of the Lt. Kernal, including the host adapter, multiplexer, hard drive(s), DOS and much additional technical information, such as installation procedures, schematics, timing diagrams and file downloads.  We hope that you find this information useful.  If you have any questions, need further information or would like to add to the site's content, please E-mail the author.

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