01.01: What old-computer hardware does the SVD support and what does "support" mean?

By "support" we mean two things:

• What old computer hardware will be able to read floppy images from the SVD?
• What old filesystems are supported?

02.01: How is the SVD connected to the floppy cable, and what do the different connectors do?

The SVD initially comes with two different edge-card connectors that connect to the left-side 34-pin header of the SVD. It is extremely important that you use one of these connectors. Please do not try to plug a floppy cable directly into the 34-pin header. The SVD uses one of the 34-pin header pins to deliver +5 to the terminated connector.

The "straight through" connector is used when there is a terminated floppy drive or another SVD physically on the floppy cable. It includes no termination.

The "terminated" connector has a resistor network on the bottom, and will effectively terminate the floppy buss. This should only be used when there is no other device terminating the floppy cable. It is always safer to try to straight through connector first.

Note, too, that the floppy or SVD with termination should be the last device on the cable (the farthest away from the computer).

03.01: What disk image formats are supported?

File Extension	Common Machine	Description
.dmk	TRS-80 1/3/4	The .dmk format is quite common for TRS-80 disk images. Originally named for its creator, David Keil, this format is a raw image of the bytes found on a TRS-80 diskette. This includes sector headers and such, although special clocks and bit transitions for FM or MFM are not represented. Most copy-protected diskettes can be represented in this format.
.jv1	TRS-80 1/3/4	Name for its creator, Jeff Vavasour, the .jv1 format is a simple contiguous set of floppy sectors. .jv1 is only used for single-sided single-density diskettes, and normally only for Model I files.
.jv1	TRS-80 1/3/4	Also named for its creator, Jeff Vavasour, the .jv3 format includes custom header information in addition to sector data. This allows some copy-protected images to be represented. Double-density diskettes are often represented in this format.
.dsk	TRS-80 1/3/4	All of the above formats (.dmk, .jv1, .jv3) can have the .dsk extension. Fortunately, due to the very different formats, the SVD can determine which format is in a .dsk file.
.jvc	TRS-80 CoCo	Name for its creator, Jeff Vavasour, the .jvc format is a hybrid of a simple contiguous set of floppy sectors and optional header information. In most cases, there is no header information and the image file contains 18-sector 256-byte contiguous data for 35 or 40 tracks.
.dsk	TRS-80 CoCo	Often used in place of .jvc in filenames. Unfortunately, the .dsk extension is extremely popular and makes guessing the format of disk images problematic. The SVD does a pretty good job of it, however.
.h17	Heathkit	One of the original formats for Heathkit H8/H89 floppy images, .h17 is a text-based (read "big") format that contains a sector by sector hex dump of the data on the disk. It includes descriptive information about the disk in the title as well. One of the nice things about this format is that it preserves the volume number of the diskette even if it is a CP/M diskette. For HDOS diskettes, the volume number is elsewhere on the image.
.h8d	Heathkit	The compact analog to the .h17 format is the binary .h8d format. This format is a binary dump of contiguous sectors from the floppy. It is assumed that there are 35 tracks of 10 256-byte sectors. So the size of these files is fixed. Note that this format is easily confused with many other binary dump formats. But, again, the SVD sorts things out pretty well...in this case based upon the file extension.
.do	Apple ][	This extension refers to DOS Ordered sectors. The data in this type of image is that only of the sector's data. In fact, the file is simply each sector of the diskette packed end to end. The SVD software understands this type of file and can order the sectors appropriately.
.po	Apple ][	This extension refers to ProDOS Ordered sectors. The data in this type of image is that only of the sector's data. In fact, the file is simply each sector of the diskette packed end to end. This file type looks JUST like the .do except that the SVD assumes a different ordering for the sectors.
.dsk	Apple ][	Often, the .dsk extension is used in place of .do. But sometimes, it will refer to .po. The SVD software will assume it is the same as .do, because it can't currently descriminate between the two. So if a .dsk won't work, try renaming it to have the .po extension.
.nib	Apple ][	The NIBble format is made up of raw sector transitions that would occur on the Apple diskette. Since it is this raw format, most copy-protected disk images will use it. The SVD software translates this image file directly to the hardware without changes.
.shk	Apple ][	Often you will see files with the ShrinkIT extension. The SVD software cannot handle this type of file directly. You will need to use either a ShrinkIT utility to unpack the file, or simply use CiderPress.
.v9t9	TI99/4a	This format is also known by .t99 and .tidisk. It is a binary data format with contiguous sectors. There is no header information and it is, therefore, impossible to distinguish between DS SD and DD SS images looking only at the size of the file. These files are normally 40 tracks with 9 sectors and in single density.
.pc99	TI99/4a	The .pc99 format is a raw dump of disk sector data and includes sector header information.
.dsk	TI99/4a	Both .pc99 and .v9t9 formats can be named a .dsk file. This often raises issues because the SVD finds it hard to distinguish between these file formats and many others. When using these formats, it is wise to name with an extension of something other than .dsk.

10.01: What type of cable do I use for my Model I?

Any 34-pin edge-card connector cable will work. However, you have to be concerned with the following issue:

• The TRS-80 floppy drives are "turned on" with ANY of the floppy drive select lines on the cable. So if you have a straight-through cable connected to more than one existing floppy, you will have problems. The original TRS-80 cable came with pulled-pins which caused only one of the floppy select signals to be sent to any particular drive...selected by the connector itself. For more information, see the TRS-80 Model I section.

13.01: Can I format the floppy image in the SVD?

In H8/89-speak, this refers to doing an init of the image in the SVD.

So can I do it? Nope! The SVD emulates floppies by generating the sector header information dynamically. This means, however, that operations that attempt to write out this information (like when formatting) will not work. In fact, they tend to confuse the crap out of the SVD, causing you to have to re-download whatever image you were using.

Fortunately, there is very few reasons to format the SVD.

14.01: Why is an extra board needed for SVD Apple 2 support?

The extra board, or dongle as it is called, converts the Apple 2 floppy control signals to the signals used by the "standard" 5 1/4 floppies of the day. For a bunch of information about the dongle, see here.

Here is a quick overview of the signals that are converted:

Head Stepping	The Apple 2 uses low-level stepper motor phase pulses to manually advance the track head through the separate tracks of the floppy. The dongle converts these phase pulses into a direction signal and a step pulse based upon the direction of the progression of the pulses. In addition, the dongle ensures that the phase pulses coming from the Apple are the appropriate width since, when booting, the Apple actually holds the phase 0 pulse high for an extended period.
Signal Polarity	The logic sense (polarity) of the Apple 2 signals are often the inverse of those for the "standard" floppy controllers. This includes inverting the read and write lines as well as creating a "motor_on" signal based upon the drive select signals.
Signal "Levels"	Closely related to the signal polarity, it is also necessary for the dongle to provide for the open-collector signals used in standard floppy controller implementations. This includes adding pull-up resistors for OC signals as well as creating an appropriate tri-state level for the read signals going back to the Apple controller.

15.01: What about double sided?