What is cache memory? How is it different from primary memory?
Definition of cache memory
Cache memory is a high speed memory built in the processor and used between the main memory and the processor.
1. Cache is memory is placed between the CPU and the main memory.
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| fig: describe the cache works between CPU & main memory. |
2. Cache memory is faster than the main memory.
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| fig: The Cache memory is faster than the main memory according to working performance. |
3. Its access time is less than the main memory.
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| fig: Cache performance of access time lower than main memory. |
4. According to measurement the cache memory access time is 10 to 30 nano second (ns) and the main memory access time is 80 (ns) nano second.
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| table of access time of both memory. |
5. The Cache memory stores instructions and data that are immediately executed.
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| fig describes that cache memory stores Instructions & Data but sometimes it don't stores data. |
6. Sometimes cache is used to store only instruction. In case that such type of cache is used in 68020 processor.
7. Cache has 256 byte instruction cache which allows it to fetching to instructions from the main memory and store them in the cache during its time period when the system bus would otherwise be idle.
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| Fig describes that when cache is uses in processor 68020 it stores only Instructions |
7. Cache has 256 byte instruction cache which allows it to fetching to instructions from the main memory and store them in the cache during its time period when the system bus would otherwise be idle.
Dependency of the cache memory according to the performance
1. Speed and size of the cache memory.
2. The logic used to read data around the memory area read by the CPU.
3. The logic used to guess next required data by the CPU.
4. With the new microprocessor you can also add external cache memory to increase the performance of the CPU.
Cache controller:
1. The
cache controller kept the frequently information in the cache memory required
by the processor.
2.
The required data by the processor in the next
memory access is available in the cache memory this process is ensured by the
cache controller.
3. The cache
controller is improves the CPU speed because if the required data is available
in the cache memory and made available for the CPU without wait state.
What is ‘Hit’ in the cache memory?
1. When
the required data is available in the cache memory it is called Hit.
2. The processor immediately reads
and writes the data in the data cache line during in the cache hit.
3. The proportion of accesses of
the results is called cache hit rate.
What is ‘Miss’ in the Cache memory?
1. When the required data is not
available in the Cache memory it is called Miss.
2. Most caches allocate new entry
which comprises the tag just missed and copy of the data from the main memory
during Miss Condition.
3. Misses are slower than the Hits
because they required data to be transferred from the main memory.
How cache memory different from the primary memory?
Primary Memory
1. The function of primary memory is
to stores information.
2. Its stores the program along
with the data to be executed.
3. It also stores the necessary programs
of the operating system or system software.
4. The executable necessary programs
for users stores in the primary memory.
5. The main memory or primary memory
is directly addressed by the CPU.
6. RAM {Random Access Memory} is
also used as main memory or primary memory.
7. It is not faster than the Cache
memory.
8. Its access time of the main
memory is 80 ns (Nano second) as comparatively slower than Cache memory.
Cache memory
1. Sometimes the used as to stores
only instructions not program.
2. It stores data and instructions
which is immediately executed.
Some points
are written above as make the difference primary memory and cache memory.
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