A tour of FatFloppy

From a filename to the sectors behind it.

Here are two disks open in FatFloppy: a Heathkit H17 CP/M image and an 8-inch Lifeboat CP/M image for the MITS Altair. The windows are arranged with disk information on the left, files in the middle, and the map or viewer on the right.

On this page: The disk map   /   Disk information   /   Reading a file

01 Seeing a file on the disk

Open the full-size disk-map screenshot · GIF, 347 KB.

Selecting MOVCPM17.COM in the file list highlights its allocation on the map. In this example, the colours mean:

Colour		What it shows
	Green	The selected file's allocation.
	Yellow	The directory area.
	Magenta	Used data blocks.
	Light grey	System tracks.
	Dark grey	Free data blocks.

The legend changes with the filesystem. Hover over a sector for its address and purpose; on a double-sided disk, use Switch Head to see the other side.

This is a logical map: sectors are drawn in order around the disk. The selected-file highlight can be approximate on interleaved or skewed layouts, including this H17 image and some RT-11 images.

02 Finding out what you opened

The Disk Information panel keeps three different things visible:

• Detected Format: the image container and the profile chosen or inferred from its contents.
• Physical Geometry: tracks, heads, sectors, sector size, and recording parameters.
• Filesystem: the file organisation, allocation details, and available space.

The H17 example has 40 cylinders, one head and ten 256-byte sectors per track: 100 KB of disk space. Its CP/M area reports 92 KB, with 4 KB free. The rest includes reserved system tracks and space outside full allocation blocks.

An H17 container can hold CP/M or HDOS. Likewise, an .img extension alone doesn't tell you which filesystem is inside. The format guide explains those combinations.

03 Reading an old document

Open the full-size file-viewer screenshot · GIF, 267 KB.

Here, MEMR.DOC is open from an 8-inch MITS Altair image. The document describes Lifeboat's memory test. The file list stays visible while the text opens beside it.

Double-click a file, or select it and choose View File. FatFloppy loads both text and hexadecimal views, bringing the likely match to the front. You can switch tabs if the guess is wrong.

The hex viewer shows offsets, byte values and printable characters. It is read-only. A file identified as text can be edited where the disk and filesystem allow writes; Save Changes writes the edit, and Discard Changes restores the loaded text. A binary file's text preview is read-only.

Extract saves the selected file to your computer. For Apollo backup files marked PARTIAL, use this command to follow the prompts for the next disk image; dragging a file out only retrieves the available portion.

Try it with your first disk image »