CAA: Christian Anime Alliance

No, actually, frame rate is not the difference, or the television could not display the signal. The frame rate on an NTSC tape at any speed is a fixed 29.97fps, just like the rate from a PAL tape is 25fps.

The primary difference is not frame rate, but track recording density. The modern VCR moves the tape over a head that is itself rotating. This results in a pattern of diagonal bands, one per interlaced frame, written over the tape at an angle. To prevent the frames from bleeding into adjacent ones and causing crosstalk/colour distortion, "guard bands" (which are just buffer blank space) are introduced between helical diagonal frames in SP mode, achieved by running the tape at a faster rate. When you slow down the tape, you can put more on it, but at the cost of squeezing these diagonal colour strips together and causing frames that have colour information bleeding between them (in SLP mode, the overlap is almost 10 microns). To improve this, modern 4-head VCRs actually have a special set of smaller heads for LP and SLP modes to read these smaller tracks, using the larger heads for SP mode for better signal fidelity. However, the same number of frames per second is still written to tape regardless.

Here are some good references for you: