Primary memory devices random access memory read only memory cache memory

1. Introduction to Computer
Lecture # 9
Course Instructor : Sehrish Rafiq
Govt. Girls Degree College Maneri Swabi
Higher Education Department KP

2. Lecture Overview
 Cache memory
 Level-1
 Level-2
 Level-3
 RAM
 SRAM
 DRAM
 ROM
 PROM
 EPROM
 EEPROM

3. Cache Memory
 Cache memory is a very high speed memory that is placed
between the CPU and main memory, to operate at the speed
of the CPU.
 CPU is the fastest component of computer but the speed of
fetching instruction from memory is normally slower than the
speed of CPU.
 As a result, the speed of CPU is also affected because for
doing its work first it has to fetch instructions from memory.
 To bridge this speed gap, Cache memory is placed between
CPU and main memory.
 The speed of cache memory is faster than main memory but is
slower than registers.

4. Cache Memory

5. Cache Memory
 Cache is cheaper than registers which justifies their use.
 Cache is used to store that data and instructions which are
frequently demanded by the running program, so that the number
of main memory accesses can be reduced.
 There are three types of cache memory.
 Level-1 cache
 Level-2 cache
 Level-3 cache

6. Level-1 Cache
 Level-1 cache is built in to the actual processor core.
 It is a piece of high speed memory which operates at the
same speed as CPU.
 It is directly accessible by the processor.
 It holds data that the processor needs to execute instructions.
 It is very expensive and small in size.
 Its typical sizes are 8,16,32,64 or 128 KB.

7. Level-2 Cache
 Level-2 cache pulls information from RAM which is then
accessed by the Level-1 Cache.
 Level-2 Cache memory is faster and smaller in size than RAM
but is slower and greater in size than Level-1 cache.
 It is less expensive than Level-1 Cache.
 Its size varies between 64 KB to 16 MB.
 The purpose of Level-2 cache is to constantly read in slightly
larger quantities of data from RAM to be available to Level-1
cache.
 Level-2 cache is mostly built in to the processor chip but in some
cases it lies on the motherboard.

8. Level-3 Cache
 Level-3 cache is specialized memory that works hand in hand
with Level-1 and Level-2 cache to improve system performance.
 Level-3 cache is the biggest cache memory.
 It anticipates data requests so that processing instructions are
provided without delay.
 Level-3 cache is faster than RAM but slower than Level-1 and
Level-2 cache.
 CPU first looks for data and instructions in Level-1 cache then it
checks Level-2 and Level-3 cache respectively.
 Level-3 cache lies on motherboard.

9. RAM
 RAM stands for Random Access Memory is the most common
type of memory found in computers.
 It is also known as main memory or primary memory.
 Instructions and data cannot be used by the processor until they
are brought in to RAM.
 It is a R/W memory and allow the computer to store and access
data and instructions randomly.
 RAM is volatile in nature which means that if the computer is
turned off or a power failure occurs all the data contained in
RAM is lost.

10. Continued…
 If the computer is turned off, all data contained in RAM is lost.
 There are two types of RAM.
 Static RAM(SRAM)
 Dynamic RAM(DRAM)

11. Static RAM(SRAM)
 SRAM is a type of semi-conductor memory.
 The word static indicates that it does not need to be
periodically refreshed to retain its data.
 SRAM is more expensive but faster and less power hungry
than DRAM.
 SRAM is mainly used to make CPU cache.
 Because of its complex structure, it is expensive and cannot
be used for high capacity storage.

12. Dynamic RAM
 DRAM is also a semi-conductor memory.
 DRAM needs to be periodically refreshed to retain its contents.
 It stores each bit of data in a separate capacitor within an
integrated circuit.
 The capacitor can be either charged or discharged.
 In personal computers DRAM is used as main memory.
 Because of their simple structure they allow high storage and
are low cost.

13. ROM
 ROM stands for Read Only Memory.
 ROM is a non-volatile memory which means that when power
goes off it does not lose its information.
 ROM is used for permanent storage of information.
 It possesses random access property like RAM.
 The contents of ROM are manufacturer supplied and cannot
be changed by users/programmers.
 There are three types of ROM.
 PROM
 EPROM
 EEPROM

14. PROM
 PROM stands for Programmable Read Only Memory.
 It is a type of ROM which can be programmed once and then can
never be changed.
 PROM is manufactured blank and then it is programmed just
once.
 The process is irreversible.
 The data is fed in to it using PROM programs.

15. EPROM
 EPROM stands for Erasable Programmable Read Only Memory.
 EPROM are non-volatile, they do not lose their content when
power supply is cut off.
 The content of EPROM chips can be erased using ultra-violet
light.
 They can be reprogrammed and reused many times.

16. EEPROM
 EEPROM stands for Electrically Erasable Programmable Read
Only Memory.
 EEPROM chips are also non-volatile.
 The content of these chips can also be erased but using
electricity instead of ultra violet light.
 EEPROM chips can also be reprogrammed many times.