Q. Is HDB-DOS fully compatible with Disk BASIC?

A. Virtually. There are some applications which either access the floppy controller hardware directly or use special copy-protected floppy disks. Those applications won't be able to take advantage of the hard disk. But for the vast majority of Disk BASIC software, HDB-DOS will work just fine. Machine language programs that utilize the DSKCON routine documented by Tandy should also work without a problem.

Q. Which hard disk controllers does HDB-DOS support?

A. Quite a few! The following SCSI controllers are supported: TC^3 from Cloud-9, Ken-Ton (no longer produced), Disto Hard Disk II (no longer produced) and Disto 4-N-1 (no longer produced). The SuperIDE and Glenside IDE interfaces are also supported.

We would like to verify support for the LR-Tech hard disk controller, but to date have not received a request for that controller.

Q. So how does HDB-DOS work?

A. HDB-DOS splits a hard drive into a number of 'virtual floppy drives' with each virtual floppy appearing just like a 35 track, single-sided, double density drive. So from a software standpoint, it looks exactly like a floppy. However, instead of accessing floppy drives 0-3, with HDB-DOS you can go all the way to drive 255.

Q. How large of a hard drive does HDB-DOS support?

A. Let's look at HDB-DOS's requirements at maximum usage. First, HDB-DOS supports a maximum of 256 virtual floppy disks (0-255). Each virtual floppy looks like a standard 35 track, single-sided, double-density floppy disk, capable of holding 161,280 bytes. With a maximum of 256 drives, this would require 161,280 x 256, or 41,287,680 bytes (41 megabytes) of storage.

Since HDB-DOS uses only the first 256 bytes of a sector, and virtually all hard drives today have 512 byte sectors, HDB-DOS will ignore, or waste, the second half of each sector on that drive. So on a 512 byte sector device, the actual space used is double, or 82,575,360 (82 megabytes). The maximum amount of hard drive space that HDB-DOS requires is 41,287,680 x (S / 256) where S is the number of bytes per sector of the hard drive.

Today's hard drives are much, much larger than 82 megabytes. Still, you can search for a smaller hard drive if you don't feel comfortable wasting a lot of space. Also, NitrOS-9 users can split their hard drives between both HDB-DOS and NitrOS-9, recouping some of the lost space. For example, a 300 megabyte hard drive will yield 218 megabytes of space for OS-9, assuming the full 256 virtual floppy drives are used. Even 218 megabytes of space is a LOT for a NitrOS-9 system on the Color Computer, so a smaller drive may be more suitable.

Q. Does HDB-DOS support 720K drives?

A. Not at the moment. The primary focus of HDB-DOS is to provide hard drive support to Disk BASIC while maintaining maximum compatibility with existing applications. We are open to the possibility of providing support for these drives, however.

Q. Why doesn't HDB-DOS fully support hard drives with 512 byte sectors?

A.Virtually all SCSI and IDE drives today use 512 byte sectors, whereas HDB-DOS as always used only the first 256 bytes of each sector, effectively wasting half of the drive's space. Unfortunately Disk BASIC, not to mention a lot of existing software, was written with the assumption that sector sizes are always 256 bytes.  Attempting to change HDB-DOS to use all 512 bytes of a sector would break compatibility with a good deal of disk utilities. We even looked at doing sector de-blocking, a common method where the drive still looks like a 256 byte sector device from a software standpoint, but decided against it because it would take up too much code space and affect performance.

Additionally, prices have dropped so much and hard drive sizes have increased in the same manner that we feel there is little justification and too much risk in changing HDB-DOS to support full 512 byte sectors.

Q. Is HDB-DOS the same as RGB-DOS, originally from RGB Computer Systems?

A. Yes, they are one and the same, with HDB-DOS being the newer, supported version. We felt that a name change was a good idea, given the time that the product had been out of support for some time. There were also several changes and additions made to the product, with more future changes possible. And along with the new name, we are also version stamping the software, starting with HDB-DOS 1.0.  This way we can keep track of changes as the product matures.

Q. I've already purchased RGB-DOS. Why should I pay for HDB-DOS?

A. HDB-DOS fixes several bugs that were found in RGB-DOS. One problem with RGB-DOS is that even though it seems to work with 512 byte sector devices, it doesn't handle disk sector reading properly, causes some machine-language programs to crash upon exection. HDB-DOS fixes this issue and several more.

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