parameters for baseline or hybrid structure are also driven from
the CACTI model. The evaluations in this paper are typically
given for a 4MB hybrid cache with 4-way SRAM and 12-way
STT-RAM array. Two extreme baseline cache configurations
are also evaluated: the fast 2MB 16-way SRAM and high dense
8MB 16-way STT-RAM. The extracted timing and energy
parameters are given in Tables I and II. Results in terms of
latency and energy per access for read operation confirm that
SRAM and STT-RAM are comparable while for the write
operation of STT-RAM is about 3x slower and consumes about
8x more energy per access. According to [12], each SRAM cell
has a size of 146F
2
while an STT-RAM cell size is about 37F
.
Hence, 2MB SRAM cache uses the same area that 8MB STTRAM
does while evaluated hybrid cache has
about 0.58 area
size
of
the
baselines.
Note,
feasibility
of
integrating
STT-RAM
technology
with
CMOS
is
previously
addressed
by
benefits
of
3D
VLSI [12].
2