Classic Computer Magazine Archive COMPUTE! ISSUE 123 / NOVEMBER 1990 / PAGE 17



I have an 80286 Harris 20-MHz system with an ITT 80287 20-MHz coprocessor and 32MB and 49MB Seagate RLL hard drives. My hard drives and floppy drives are all controlled through one RLL controller card. I want to add a tape drive to my system, but I've heard some funny stories about the interaction of RLL hard drives and tape backup systems. I've been told that even though the tape drive would come with its own controller card, it won't work with an RLL system attached to the motherboard. Please tell me if this is true and why.


RLL (Run Length Limited) and MFM (Modified Frequency Modulation) are two techniques frequently used for encoding data on a hard disk.

An RLL controller transfers data at 750 kilobytes per second and manages up to two disk drives of up to 200 megabytes capacity each. If both your hard drive and controller use the RLL format, you can stretch a 20-megabyte hard disk into 30 megabytes of data storage. Although the RLL method is faster, MFM is the most commonly used format for hard disks under 80MB.

We contacted several tape and hard disk drive manufacturers, none of whom had heard of the incompatibility you described. We suggest that before buying a tape drive system, you make sure the system can be returned if it doesn't work on your computer.

If you have trouble after the tape drive is installed, contact the company's technical department to make sure it's installed properly. Several of the manufacturers we contacted have toll-free technical support numbers.