  We present basic properties of protostellar disks in the embedded phase of
star formation (EPSF), which is difficult to probe observationally using
available observational facilities. We use numerical hydrodynamics simulations
of cloud core collapse and focus on disks formed around stars in the 0.03-1.0
Msun mass range. Our obtained disk masses scale near-linearly with the stellar
mass. The mean and median disk masses in the Class 0 and I phases
(M_{d,C0}^{mean}=0.12 Msun, M_{d,C0}^{mdn}=0.09 Msun and M_{d,CI}^{mean}=0.18
Msun, M_{d,CI}^{mdn}=0.15 Msun, respectively) are greater than those inferred
from observations by (at least) a factor of 2--3. We demonstrate that this
disagreement may (in part) be caused by the optically thick inner regions of
protostellar disks, which do not contribute to millimeter dust flux. We find
that disk masses and surface densities start to systematically exceed that of
the minimum mass solar nebular for objects with stellar mass as low as
M_st=0.05-0.1 Msun. Concurrently, disk radii start to grow beyond 100 AU,
making gravitational fragmentation in the disk outer regions possible. Large
disk masses, surface densities, and sizes suggest that giant planets may start
forming as early as in the EPSF, either by means of core accretion (inner disk
regions) or direct gravitational instability (outer disk regions), thus
breaking a longstanding stereotype that the planet formation process begins in
the Class II phase.
