1. Memory and Repetitive Arithmetic Machines
Prof. Sirer
CS 316
Cornell University

2. Memory Various technologies Static-RAM Dynamic-RAM Non-Volatile RAM
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 to 1M writes, NV-RAM degrades

3. S-RAM Data A decoder selects which line of memory to access
A R/W selector determines the type of access
That line is then coupled to the data lines
How do you build large memories?
Address
Decoder

4. Tristate Buffers
A device that couples a logic line to a wire

5. Big Memories data enable
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 2 12
addr

6. Summary
We now have enough building blocks to build machines that can perform non-trivial computational tasks

7. 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) 8 …
reg 8
adder
led-dec 8 8 …
reg
mux 8 1
mux
add/sub select
doit

8. A Vote Counter 8
led-dec
reg
Data values flow from set of parallel registers (a register file)
to the addition unit
back into the register file 8 s1 ..
mux 8
reg 1
clk s4 s4 s3
reg
enc
deco s2 s1