This paper presents a series of global three-dimensional accretion disk sim
ulations carried out in the cylindrical limit in which the vertical compone
nt of the gravitational field is neglected. The simulations use a cylindric
al pseudo-Newtonian potential, proportional to 1/(R - R-g), to model the ma
in dynamical properties of the Schwarzschild metric, The radial grid domain
runs out to 60R(g) to minimize the influence of the outer boundary on the
inner disk evolution. The disks are initially constant density with a Keple
rian angular momentum distribution and contain a weak toroidal or vertical
held that serves as the seed for the magnetorotational instability. These s
imulations reaffirm many of the conclusions of previous local simulations.
The magnetorotational instability (MRI) grows rapidly and produces MHD turb
ulence with a significant Maxwell stress that drives accretion. Tightly wra
pped low-m spiral waves are prominent. In some simulations radial variation
s in Maxwell stress concentrate gas into rings, creating substantial spatia
l inhomogeneities. As in previous global simulations, there is a nonzero st
ress at the marginally stable orbit. The stress is smaller than seen in str
atified torus simulations but nevertheless produces a small decline in spec
ific angular momentum inside the last stable orbit. Detailed comparisons be
tween simulations are used to examine the effects of various choices in com
putational setup. Because the driving instability is local, a reduction in
the azimuthal computational domain to some fraction of 2 pi does not create
large qualitative differences. Similarly, the choice of either an isotherm
al or adiabatic equation of state has little impact on the initial evolutio
n. Simulations that begin with vertical fields have greater field amplifica
tion and higher ratios of stress to magnetic pressure compared with those b
eginning with toroidal fields. In contrast to MHD, hydrodynamics alone neit
her creates nor sustains turbulence.