ICT role in 21st century education and it's challenges.
20042602207.pptx
1. Unit -5
Department of Computer Science - Kamban
College of Arts And Science For Women
2. SYLLABUS
Auxiliary memory – Main memory – Associative memory – Cache memory
– Virtual memory
Department of Computer Science - Kamban
College of Arts And Science For Women
3. AUXILIARY MEMORY
It is used to overcome the limitations of primary storage
Unlimited capacity because the cost per bit of storage is very low
Larger capacity than main memory
Used to store large volumes of data on a permanent basis
It is non-volatile in nature
Also known as secondary memory
Department of Computer Science - Kamban
College of Arts And Science For Women
7. MAIN MEMORY
Memory unit that communicates directly with CPU
Programs and data currently needed by the processor reside here
Also known as primary memory
RAM and ROM
Department of Computer Science - Kamban
College of Arts And Science For Women
10. ASSOCIATIVE MEMORY ORGANIZATION
Associative memory is organized in such a way
Argument register(A): It contains the word to be searched. It has n bit (one
for each bit of the word)
key register(K): This specifies which part of the argument word needs to
be compared with words in memory. If all bits in register are q. the entire
word should be compared. Otherwise only the bits having k bit set to 1 will
be compared
Associative memory array: It contains the words which any to be
compared with the argument word
Match register(M): It has m bits. One bit corresponding to each word in
the memory array. After the matching process, the bits corresponding to
matching words in match register are set to 1
Department of Computer Science - Kamban
College of Arts And Science For Women
12. DISADVANTAGES OF ASSOCIATIVE MEMORY
Department of Computer Science - Kamban
College of Arts And Science For Women
13. ADVANTAGES OF ASSOCIATIVE MEMORY
Department of Computer Science - Kamban
College of Arts And Science For Women
14. CACHE MAPPING
There are most common methods available in cache mapping. They are,
• Direct Mapped Cache
• Associative Mapped Cache
• Set- Associated Mapped Cache
Department of Computer Science - Kamban
College of Arts And Science For Women
15. DIRECT MAPPING
Each block of main memory maps to only one cache line
i.e., if a block is in cache, it must be is one specific place
Address is in two parts;
• Least significant w bits identify unique word
• Most significant s bits specify one memory block
Department of Computer Science - Kamban
College of Arts And Science For Women
16. DIRECT MAPPING ADDRESS STRUCTURE
24 bit address
2 bit word identifier(4 byte block)
22 bit block identifier
8 bit tag(=22-14)
14 bit slot or line
Department of Computer Science - Kamban
College of Arts And Science For Women
17. DIRECT MAPPING FROM CACHE TO MAIN MEMORY
Department of Computer Science - Kamban
College of Arts And Science For Women
18. DIRECT MAPPING CACHE ORGANIZATION
Department of Computer Science - Kamban
College of Arts And Science For Women
19. ADVANTAGES
The tag memory is much smaller than in associative mapped cache
No need for an associative search, since the slot field is used to direct the
comparison to a single field.
DISADVANTAGES
Consider what happens when a program references locations that are 219
words apart, which is the size of the cache. Every memory reference will
result in a miss, which will cause an entire block to be read into the cache
even though only a single word is used
Department of Computer Science - Kamban
College of Arts And Science For Women
20. ASSOCIATIVE MAPPED CACHE
A main memory block can load into any line of cache
Memory address is interpreted as tag and word
Tag uniquely identifies block of memory
Every lines tag is examined for a match
Cache searching gets expensive
Department of Computer Science - Kamban
College of Arts And Science For Women
22. ADVANTAGES
Any main memory block can be placed into any cache slot
Regardless of how irregular the data and program references are, if a slot is
available for the block, it can be stored in the cache
DISADVANTAGES
Considerable hardware overhead needed for cache bookkeeping
There must be a mechanism for searching the tag memory in parallel
Department of Computer Science - Kamban
College of Arts And Science For Women
23. SET ASSOCIATIVE MAPPING
Cache is divided into a number of sets
Each set contains a number of lines
A given block maps to any line in a given set
E.g. Block B can be in any line of set I
2 way associative mapping
Department of Computer Science - Kamban
College of Arts And Science For Women
25. ADVANATAGES
In our example the tag memory increases only slightly from the direct
mapping and only two tags need to be searched for each memory reference
The set-associative cache is widely used in today’s micro processors
Department of Computer Science - Kamban
College of Arts And Science For Women