A biphasic schedule is a sleep schedule which contains two blocks of sleep.
Biphasic schedules have been naturally used by humanity over the centuries. Their mechanism is mostly not the same, and only high total sleep time is a similar feature. Less reduction is possible because of the wake time reduction mechanism, as biphasic schedules have only two blocks of sleep, which is not enough to sleep much less than on monophasic sleep. The maximum possible reduction is usually around 1-3 hours. All the biphasic schedules also belong other polyphasic schedules categories.
Siesta sleep generally consists of a long core at night and a shorter core (siesta nap) midday. Siesta sleep tends to have around 6-8 hours of total sleep time.
This schedule also belongs to the dual core category by the amount of cores, albeit the mechanism is quite different from segmented/bifurcated sleep. By the mechanism this schedule is mostly similar to core-only schedules, such as Triphasic sleep or QC0.
Segmented sleep, sometimes denoted as DC0 (dual core with zero naps), has one core sleep generally around dusk and one core sleep generally around dawn a few hours after the end of the dusk core. Segmented sleep tends to have around 6-8 hours of total sleep time.
This schedule belongs to the dual core category both by the amount of cores and by the mechanism of segmentation and is a nice starting point for the gradual adaptation to DC schedules.
E1 or Everyman 1 consists of a long core at night and a nap midday. It tends to have around 6-7 hours of total sleep time as well. An extended version is possible for underaged people as well as those with higher sleep requirements.
This schedule also belongs to the everyman category both by the amount of cores and by the mechanism of replacing one sleep cycle with one nap, and is a nice starting point for the gradual adaptation to Everyman schedules.
BiphasicX is a flexible non-reducing biphasic sleep schedule, which consists of two blocks of sleep of any length. This schedule can combine all the other biphasic schedules. Usually it takes form of a non-reducing E1 / Siesta, having a long core at night and a short nap / core midday. However, a Segmented-oriented variant is also possible.
This schedule has a potential for those, who needs a great sleep flexibility since the very beginning, as the adaptation is usually very mild and the absence of sleep reduction makes it possible to have a wider flex range.