Semi-Virtual Diskette (SVD)

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The SVD is no longer in production. Sorry!

Getting Started

You've just received your SVD - now what do you do? Click here!.

Semi-Virtual Diskette (SVD) Introduction

  The SVD is a small hobbyist hardware device that emulates an old floppy drive. Through an RS232 interface on your Windows or Linux box, you can download a floppy image to the SVD and then boot your favorite old program on your old machine just as if you had the floppy disk itself.  With the included software, you can easily run entire diskette images or single files such as BASIC programs.  The SVD was created originally for the TRS-80, but has expanded to include the Heathkit H8, Apple ][ and others.

The little diagram below shows the SVD connected to an Apple //+.  The SVD is depicted about twice real size. You can see the actual size of the SVD in the picture below that (the one with the cover off of the SVD - that's my hand).

Apple ][ Floppy cable SVD RS232 Cable PC Connects to SVD with RS232

Floppy Cable


RS232 Cable

What is the SVD good for?

  • You can run your favorite old program on your old hardware easily, and without making any modifications to your old machine...the SVD looks just like a floppy drive to it.You don't have to open up your PC either.
  • You can easily create a real floppy disk of your favorite program or DOS by booting DOS from the SVD and running the standard backup program targeting a blank floppy in one of your existing drives
  • You can back-up or make "images" your exiting software collection, saving it for posterity.These images are loaded up to your PC in standard formats.
There are some pretty nice ways to get software to and from your old machine, but the SVD is probably the easiest. You don't have to open up a single computer, either the target old machine or the PC. Further, you don't have to have a spare 5 1/4 inch PC drive laying around. For the SVD, you just need a old machine with floppy drive capability (like the expansion interface for the TRS-80) and a PC with an RS232 port running either Windows or Linux. Sure, you need some floppy images too.

The SVD is based upon a PIC micro-controller along with some memory. It listens to the floppy control signals from your old computer and generates the appropriate "floppy-looking" signals back, convincing it that it is talking to a real floppy drive. The old machine will then blissfully boot and read from the SVD.

The SVD is plugged into your Windows or Linux box through a standard RS232 (serial) port, operating between 9600 and 115200 baud. Through programs running on your PC, you down/up-load the SVD and control its operation. The PC interface includes capability to read/write "standard" diskette formats.


The SVD is a "work in progress" and has the following features. Note that some of the features aren't checked-off. In some cases, the feature is not planned. In others the feature is in the works. In these cases, the hardware platform supports the feature, but it's now simply a matter of software. :-)

One feature in particular, double sided, isn't supported by the hardware because memory requirements for DS DD (the most popular use of double sided) are more than the 256K currently on board. Apologies to the TI99/4a fans who really need DS SD now...I know that MANY of the TI99/4a disk images are double sided.

Each individual platform that the SVD supports has its own set of supported features, too.  So please take a look at your desired machine to see any notes or modifications to this feature set.

Up to three diskette images can be loaded at once (drive 0, 1, and 2) up to 256k
single-sided single density (SS SD)
double density (SS DD)
double-sided - the SVD II (coming someday :-) will support DS DD and DS SD with 1MB of memory
reading/booting the diskette image
writing the diskette image
pretty LEDs for power, drive0/1/2, track0, and write

TRS-80 Support (Model 1, 3, 4, 4P and CoCo)
Heathkit Support (H8, H89)
TI99/4a Support - not including DS SD, see above
Apple ][ support
Write capability for Apple ][ disks

Runs most copy-protected software
Can copy or back-up "normal" software
Can copy or back-up copy-protected software
The SVD was built for fun, and was built with parts that were easy to come by and easy to use. Total parts cost is around $60. Schematics, board layout, and all software can be found here, so feel free to build one yourself. What I recommend, though, is that you just buy one here. I don't intend to make any money off of the SVD; whatever profit beyond the cost of parts will be donated to worthy vintage computer sites and concerns.