2. Methods of Address
Mapping :
There are three commonly used methods to
translate main memory addresses to cache
memory addresses.
• Direct-Mapping
• Associative Mapping
• Set-Associative Mapping
3. BLOCK: Fixed sized packet of information that
moves back and forth between a cache and main
memory.
LINE: Container in a cache that stores a block
as well as other information such as the valid bit
and tag bits.
SET: Collection of one or more lines. Sets in
direct-mapped caches consist of a single line.
Set in fully associative and set associative
caches consists of multiple lines.
6. • Each cache slot corresponds to an explicit
set of main memory.
• In our example we have 4096 memory
blocks and 128 cache slots.
• 128 blocks of main memory save in 1
block of cache memory.
• It is simplest mapping technique.
• It is easy to implement.
7. Advantages:
• The tag memory is much smaller than in
associative mapped cache.
• It is less costly compare to other mapping
technique.
Disadvantages:
• It is not flexible.
8.
9. Associative Mapping
• Any main memory blocks can be
mapped into each cache slot.
• The 12-tag bits are required to identify a
memory block when it is in the cache.
10. • The mapping from main memory blocks to
cache slots is performed by partitioning an
address into fields.
• There is no fix block, the memory address
has only two fields : Tag & Word.
11. Advantage:
• Flexibility. Main Memory block can be mapped
anywhere in Cache Memory.
Disadvantage:
• Slow or expensive.
12.
13. Set-Associative Mapping
• Combines the simplicity of direct
mapping with the flexibility of associative
mapping.
• For this example, two slots make up a
set. Since there are 214 slots in the
cache, there are 214/2 =213 sets.
14. • When an address is mapped to a set, the
direct mapping scheme is used, and then
associative mapping is used within a set.
• The format for an address has 13 bits in the
set field, which identifies the set in which the
addressed word will be found. Five bits are
used for the word field and 14-bit tag field.
15. Advantages:
• 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 microprocessors.
