Computer media images

When working with computer simulators (e.g. SIMH), you usually use images of computer media instead of real ones. (Well, some simulators can even be run with real media, too.)

Another scenario is preservation and copying of old computer media.

There are:

• Floppy disk images
• Hard disk images
• Magnetic tape images
• Paper tape images
• Punched card images
• etc.

The multitude of image formats as well as their characteristics can sometimes be really confusing.

I'll try to shed some light on some common image media formats and manipulation tools.

Image format basics

Regardless of the media involved, two basic types of images can be distinguished:

• Raw data images
• Images containing additional metadata and/or using compression

Both types have their specific pros and cons and areas of application.

Raw data images are mainly used with simulators, whereas "metadata enriched" images are more common for data preservation and copying of computer media.

Raw data images have two subvariants:

• Raw data images in sector/physical order (dependent on sector interleaving applied)
• Raw data images in logical/LBN order (independent of interleaving)

SIMH for example expects images in logical order, whereas Xhomer depends on sector order.

Imaging tools/toolkits

ImageDisk

ImageDisk

SAMdisk

SAMdisk

Further Reading

• Disk Imaging Techniques