2. Topics
History of memory
Memory
Types of memory

3. History of memory
In the early 1940s, memory technology mostly
permitted a capacity of a few bytes.
ENIAC(Electronic Numerical Integrator And Computer):
Firs electronic general-purpose computer . That is
capable of being reprogrammed to solve a large class
of numerical problems.

4. Vacuum
tubes.
The first electronic
programmable digi
tal computer
the ENIAC, using
thousands of octal-
base radio vacuum
tubes could
perform simple
calculations
involving 20
numbers of ten
decimal digits

5. delay line memory:
 developed by J. Presper Eckert in the early 1940s.
It is also used in digital computers.
 Delay line memory would be limited to a capacity of
up to a few hundred thousand bits to remain
efficient.

6. random access computer memory
the Williams tube and Selectron tube originated in
1946.
 in 1947 Jay Forrester, Jan A. Rajchman and An
Wang developed magnetic core memory which
allowed for recall of memory after power loss.

7. random access computer memory.
the
Selectron
was limited
to 256 bits,
while the
Williams
tube could
store
thousands

8. Magnetic core memory
•It was the
computer
memory of
choice
throughout
the 1960s,
until it was
replaced by
semiconduc
tor memory.

9. Memory
.
 Electronic components that store instructions, data,
and results
 Consists of one or more chips on motherboard or
other circuit board
 Each byte stored in unique location called an
address.

10. Memory
It holds the data and instructions that the Central
Processing Unit (CPU) needs.
Before a program can be run the program is loaded
from the storage medium into memory.
It allows the CPU to direct interact with the
program.
Memory is a need of every computer

11. Memory
Memory chips almost always come as part of a card
called a module.
Memory's usually listed with two numbers, such as
8x32 or 4x16.
The first number represents the number of chips on
the module.
The second one tells the capacity of each individual
chip, measured in megabits (Mb), or one million bits.

13. Types of memory
1. ROM (Read Only Memory)
2.RAM (Random Access Memory)
3.Cache
4.Flash memory

14. ROM
stores data without
electrical current;
it is the ROM
(Read Only
Memory)
or is sometimes
called non-volatile
memory as it is not
erased when the
system is switched
off
Read Only Memory

15. Types of ROM
PROM (Programmable Read Only Memory)
EPROM (Erasable Programmable Read Only
Memory)
EEPROM (Electrically Erasable Read Only Memory .

16. PROM
Programmable read-only memory (PROM) is a blank
ROM chip on which a programmer can write
permanently, but once written cannot be changed or
modified
ROM cannot be written when the computer is
running.
ROM use for important program like BIOS or the
firmware of a device.

17. PROM
.
Once
a program has
been written
onto a PROM, it
remains there
forever.

18. But most ROM chips designed to be modified by
users, use
Erasable programmable read-only memory
( EPROM)
or electrically erasable programmable read-only
memory ( EEPROM).

19. EPROM
An EPROM or erasable programmable read only
memory, is a type of memory chip
 Once programmed, an EPROM can be erased with
the help of ultraviolet light

20. EEPROM
Electrically Erasable Programmable Read-Only
Memory
Type of PROM that can be erased by exposing it to
an electrical charge.
Similar to EPROM.

21. Memory
How is memory measured?
Term Abbreviation Approximate Size
Kilobyte KB or K 1 thousand bytes
Megabyte MB 1 million bytes
Gigabyte GB 1 billion bytes
Terabyte TB 1 trillion bytes
 By number of bytes available for storage

22. RAM
Random Access Memory, can be accessed
randomly. Any byte of memory can be accessed without
touching the preceding bytes. RAM is the most
common type of memory found in computers and other
devices, such as printers.

23. Memory
What is random access memory (RAM)?
p. 195
The more RAM aThe more RAM a
computer has, thecomputer has, the
faster it respondsfaster it responds
Also calledAlso called
main memorymain memory
oror primaryprimary
storagestorage
Most RAM isMost RAM is
volatilevolatile, it is lost, it is lost
when computer’swhen computer’s
power ispower is
turned offturned off
Memory chips that can beMemory chips that can be
read from and writtenread from and written
to by processorto by processor

24. RAM
RAM is mostly sold in multiples of 16 megabytes: 16,
32, 64, 128, 256, 512 and 1,024 (the same as 1GB) .
DDR2 and DDR3 RAMs.
DDR2
Appears in 2004 (speed: delivering bandwidth of up
to 8.5 GB per second)
DDR3
Appears in 2007(speed : can transfer data at rates up
to 12.8 GB per second)

25. DDR2 DDR3
RAMs

26. Types of RAM
There are two different types of RAM:
DRAM (Dynamic Random Access Memory)
SRAM (Static Random Access Memory).
DRAM:
 Needs to be refreshed thousands of times per second
while.
Dynamic RAM needs to automatically refresh thousands of
times per second; that's where it gets the name dynamic.
Otherwise, it will forget the information it's holding.

27. DRAM

28. SRAM
Does not need to
be refreshed,
which is what
makes it faster
than DRAM.
Both types of
RAM are volatile,
meaning that
they lose their
contents when
the power is
turned off.

29. Memory
Where does memory chips
reside?
 Memory slots on
motherboard hold memory
modules
memory chip memory slot
dual inline memory module

30. Cache memory
Helps speed computer processes by storing frequently
used instructions and data
The cache is a smaller, faster memory which stores
copies of the data from frequently used main
memory locations.

31. Cache memory
When the processor needs to read from or write to a
location in main memory, it first checks whether a
copy of that data is in the cache. If so, the processor
immediately reads from or writes to the cache, which
is much faster than reading from or writing to main
memory.

33. Flash Memory
Non volatile memory can be erased electronically
and rewritten similar to EEPROM.
Introduced by Toshiba in 1984
Most computers use it to hold up their startup
instructions
Also used in many mobiles , smart phones ,
digital cameras and PDA

34. Flash memory
There are two main types of flash memory.
1. NAND
2.NOR
 NAND type flash memory may be written and read
in blocks.
 NOR type flash allows a single machine word(byte)
to be written to an erased location or read​
independently.

36. What is capacity
.
Kilobyte (KB) 1 thousand
Megabyte (MB) 1 million
Gigabyte (GB) 1 billion
Terabyte (TB) 1 trillion
Petabyte (PB) 1 quadrillion
Number of bytes (characters) a storage medium can hold
Exabyte (EB) 1 quintillion
Zettabyte (ZB) 1 sextillion
Yottabyte (YB) 1 septillion

37. Memory
Smallest unit: bit
8 bit = 1 byte
1024 byte = 1 kb (kilo byte)
Each byte is able to represent 255 different number
(0 to 255)