Internal memory

Computer Architecture

1. Internal MemoryInternal Memory

2. IntroductionIntroduction
Computer memory exhibits different types
of technique, organization, performance,
size and cost.
But, no technology is optimal in memory
requirements for a computer system.
As a result, a computer equipped with a
hierarchy of memory subsystems.
Some are internal to the system – RAM,
ROM, CACHE
External memories are Hard disk, Optical
and Pen drive etc.,

3. RAMRAM
Storage cell unit consists of N cells each of
which can store 1 bit either 0 or 1.
Every location of RAM accessed
independently. So, the access and cycle
times can constant.
The address of memory location transferred
through MAR using address bus.
The address then proceed by the address
decoder.
Which select required location in storage
unit.

4. RAM contd.,RAM contd.,
The contents of the selected location placed
in IR through MDR processor register.
The R/W control line specifies the type of
access to be performed.
Write operation, the word to be place in
MDR and the address specified in MAR
and then transferred to selected cell.
DDR RAM-Double Data Rate
synchronous dynamic random access
memory

5. RAMRAM

7. ROMROM
Data are written into a ROM when it is
manufactured.
ROM is mask programmed by the
manufacturer in the factory with the
contents ordered by the customers.
The contents are fixed by metal masks used
during chip fabrication.
Once programmed, the contents cannot be
erased.
Even a single bit wrongly programmed the
ROM chip is useless.

8. ApplicationApplication
Used to store control programs such as
micro program.
Character generation, code conversion, etc.,

10. Boot screenBoot screen

13. PROM-Programmable ROMPROM-Programmable ROM
PROM is a field programmable device.
The customer buy a blank PROM and store
desired data using PROM programmer(burner).
Programmability achieved by inserting a fuse at
point P.
Before programmed, the memory contains all 0s.
The user can insert 1 by burning out the fuse in the
particular cell using high current pulse.
The PROM chip can be programmed only once
and its contents cannot be erased.
PROM are flexible , faster and less expensive
because they can be programmed directly by the
user.

14. Application-PROMApplication-PROM
Boot program in micro computer

15. PROMPROM

16. PROMPROM

17. EPROM-Erase programmable ROMEPROM-Erase programmable ROM
A rewritable chip that holds its contents
without power.
Previous data can be erased and new data
can be inserted
EPROM chips are written on an external
programming device before being placed on
the circuit board.
Capable of retaining stored information for
a long time.

18. EPROM contd.,EPROM contd.,
Eraser requires breakup the charges trapped
in the transistors of memory cell.[this is
done by break the chip to ultraviolet light].
This reason EPROM packaged with
transparent window.
Disadvantages:
Entire EPROM is erased as a whole and
selective erasing is not possible.
Should be removed from the chip for
reprogramming.

19. EPROMEPROM

21. EEPROM-Electrically Erased PROMEEPROM-Electrically Erased PROM
It can be both programmed and erased
electrically( flashed back to Zero).
They do not need to removed when the chip
content erasure.
Also, erase selected content in the chip.
Erasing and programming dynamically
without removing the EEPROM from the
circuit.
Disadvantages:
Different voltages are required for erasing,
reading and writing the data.

22. ApplicationApplication
Used as ROM
Critical system setup information in a non-
volatile way.

23. EEPROMEEPROM

24. EEPROMEEPROM

25. EEPROMEEPROM

26. Flash MemoryFlash Memory
Recent kind of EEPROM is flash memory.
Which is erased by ultraviolet light.
EEPROM is byte erasable whereas, flash
memory is a block erasable.
Like a EEPROM when erasing the contents
of flash memory no need to remove from
the circuit.
In flash it is possible to read the contents of
a single cell, but is only possible to write an
entire block of cells.

27. Flash memory contd.,Flash memory contd.,
It need single power supply and consume
less power.
Application:
Cell phones, hand held devices, digital
camera, washing machine, AC, Tablet etc.
NOTE: low power consumption of flash
memory makes it attractive for use in
portable equipment that is battery driven

28. Flash CardFlash Card
Mount flash chips on a small card.
That card simply plugged into a slot.
64 MB can store 1 hour songs.
Now a days, the device can equipped with
up to 32GB flash memory.

32. Speed, size and CostSpeed, size and Cost
SRAM chip is very fast memory in the computer
system. but it is expensive because their basic
cells have 6 transistors.
Which impossible to packaging a very large
number of cells onto a single chip.
Cost wise also expensive.
Cache memory can be implemented based on
SRAM.
Alternative is to use DRAM, which can have same
basic cells and thus much less expensive. But
significantly slower.
Still it is small in size compared to magnetic
drives.

33. Speed, size and CostSpeed, size and Cost
Main memory can be build with DRAM.
Secondary storage- large memory space with
reasonable price but much slower than
semiconductor memory unit.

34. conclusionconclusion
Huge amount of cost-effective storage can
be provided by magnetic disk.
Main memory can be built with DRAM.
SRAM to be used in smaller unit where
speed is of the essence.(Cache)

35. SPEEDSPEED

36. SPEEDSPEED
Fastest access is to data held in processor
registers.
There are often two levels of cache, the
primary cache inside processor refer to as
L1. secondary cache placed outside
referred as LEVEL 2(L2) usually SRAM
chip.
Next level in the hierarchy is called main
memory.
The typical main memory is about ten
times slower than the access for the L1
cache.

37. SPEEDSPEED
The bottom level in the hierarchy is called
the secondary memory such as magnetic
disk.
Disk provide a huge amount of
inexpensive storage. But they very slow.