1. Memory types ROM – Read only memory RAM – Random Access Memory
Word – a group of n bits processed as one word

2. ROM – Read only memory
Holds 2n words of m bits
n bits
m bits

3. ROM – Read only memory 25x4 example
Address
Word
00000
1010
00001
1110
00010
1101 …

4. ROM – Read only memory 25x4 exampleA0 1 2 A1 A2 A3 A4 31 F3 F2 F1 F0

5. ROM – Read only memory A0 1 2 A1 An 2n
מגשרים Fm F0

6. ROM Types ROM/PROM EPROM the bridges are permanent.
“Programming” using other units (or in the factory).
EPROM
Can be reinitialized.

7. ROM with unusable combinations
12 bits
Alpha numeric code
(only 47 combinations)
ROM 12
bits 6
bits

8. ROM with unusable combinations
ROM - 12 entrances = 4096 words
Using 47 words
Wasting 4049 words

9. PLA – Programmable Logic Array
Bridge
n x k
Bridge
m OR
k AND m
outputs n
entrances
k x m
Bridge
n x k
Bridge

10. PLA – Programmable Logic Array
Typical PLA
16 entrances
48 and elements
8 outputs

11. RAM – Random Access memory
Properties
Can represent 2 bits
Small dimensions
Minimum Cost
Reasonable access time

12. RAM - Random access memory
m bits
0 …………………………1
Memory
Address Register
Read/Write
n words
Buffer Register
Outgoing
data
Ingoing
data

13. RAM – Random Access Memory Basic Cell Unit
Write = 0
Read = 1

14. RAM – Random access memory (basic cell)

15. RAM – Random access memory (basic cell)