These terms describe techniques to write data on disks. In the iside of a hard drive, several magnetic disks rotate, which are written on or read from with write and read heads.
The usual method of storing data as magnetic information is Perpendicular Magnetic Recording, or PMR. Here, the data (ie the consecutive zeros and ones) are written one behind the other on your track. The special feature is the arrangement of the magnetic information: Like a magnet with a positive and a negative pole, the magnetic information has two ends. In order to accommodate as many of them as possible in a small space, you do not simply write them one after the other, but rather into the depths. So you stack the magnetic bits vertically next to each other (perpendicular). This gives you a very high data density, but it is still possible to overwrite all areas without loss of speed again and again.
To squeeze even more data onto a magnetic disc, Shingled Magnetic Recording, or SMR, has been developed. This allows an 25% higher storage density. But where does the magnetic disk get the additional amount of space from? Well, you do cheat a bit. While the tracks are written cleanly next to each other with PMR, the SMR system writes a new track slightly over an already existing one and just leaves so much untouched that the information is still readable. The name “shingled” comes from shingle and refers to the overlapping approach. The problem with this is that traces that contain information must also be rewritten in this process. You can not just write a new track with new information, you have rewrite all tracks that get touched in this process
This is a huge disadvantage when very large amounts of new data have to be written and a very large amount of existing data must be re-sorted and rewritten, so that data rates fall sharply. As a result, hard drives using this technology are suitable as archive drives that are rarely written but often read, and drives that sometimes add several gigabytes of data (but not several hundred at a time).
