Transcript Memory Basics

Memory and Repetitive
Arithmetic Machines
Prof. Sirer
CS 316
Cornell University
Memory
Various technologies

S-RAM, D-RAM, NV-RAM
Static-RAM


So called because once stored, data values are stable as long
as electricity is supplied
Based on regular flip-flops with gates
Dynamic-RAM


Data values require constant refresh
Internal circuitry keeps capacitor charges
Non-Volatile RAM



Data remains valid even through power outages
More expensive
Limited lifetime; after 100000 to 1M writes, NV-RAM degrades
Data
S-RAM
A R/W selector determines the
type of access
Decoder
Address
A decoder selects which line of
memory to access
That line is then coupled to
the data lines
How do you build large
memories?
Tristate Buffers
A device that couples a logic line to a wire
Big Memories
data
enable
2
Memory banks in
parallel, with tri-state
buffer and decoder to
select which bank to
couple
The enable bit controls
connection of data bits
and clocking of internal
flip-flops
12
addr
Summary
We now have enough building blocks to build
machines that can perform non-trivial
computational tasks
8
add/sub select
doit
0
1
8
led-dec
8
mux
mux
reg
…
8
adder
8
reg
…
A Calculator
User enters the numbers
to be added or
subtracted using toggle
switches
User selects ADD or
SUBTRACT
Muxes feed A and B,
or A and –B, to the 8-bit
adder
The 8-bit decoder for the
hex display is
straightforward (but not
shown in detail)
s1
mux
reg
8
reg
8
1
Data values flow
from set of parallel
registers (a register
file)
to the addition unit
0
back into the register
file
reg
s4
enc
clk
8
deco
..
led-dec
A Vote Counter
s4
s3
s2
s1