1. Jazan University, Jazan KSA
Chapter 4
Lecture 09
Faheem Ahmad
Lecturer, CNET Dept.,
Jazan University, Jazan KSA
Cache Memory

2. Topics of this chapter Computer memory system Cache Memory Principles
Elements of cache design
Replacement algorithms

3. Computer memory system
The topic computer memory system can be understood by the study of Key Characteristics of Computer Memory Systems.
Location,
Capacity,
Unit of Transfer,
Access Method,
Performance,
Physical Type,
Physical Characteristics and Organization
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4. Characteristics of Memory
Location
Internal , External
Capacity
Number of words, Number of bytes
Unit of Transfer
Word, Block
Access Method
Sequential, Direct, Random, Associative
Performance
Access time, Cycle time, Transfer rate
Physical Type
Semiconductor, Magnetic, Optical, Magneto-optical
Physical Characteristics
Volatile/nonvolatile, Erasable/non erasable
Organization
Memory modules
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5. KEY CHARACTERISTICS OF MEMORY
LOCATION
1.Internal: Registers, main memory, cache
2.External:Disk,Tape, flash drive
CAPACITY
Expressed in bytes or words.
UNIT OF TRANSFER
Is number of bits read out or written into memory.
Expressed in word or block of data

6. CONT…..
ACCESS METHODS
1.Sequential Access: In this access method data is retrieved in same order in which thy have been stored.
2.Direct Access: Data is read directly from location
3.Random Access: Data is searched randomly used a technique called hashing.

7. Sequential and random

8. Direct access

9. performance
1. Access time : Time it takes to perform a read or write operation.
2.Memory cycle time: Access time + additional time to required before second access
3.transfer Rate: is the rate at which data can be transferred in or out of memory.
NOTE: for RANDOM ACCESS MEMORY
Tr= 1/cycle time
For NON-RANDOM Tn=Ta+n/r

10. Memory Hierarchy As one goes down the hierarchy, the following occur:
Decreasing cost per bit
Increasing capacity
Increasing access time
Decreasing frequency of access of the memory by the processor

11. Characteristics of memory hierarchy
RULES OF HIERARCHY
Faster access time, greater cost
Greater capacity, smaller cost
Greater capacity, slow access time
As we go down of memory hierarchy we see following
Decreasing cost
Increasing capacity
Increasing access time
Decreasing frequency

12. Cache Memory
A small amount of fast memory that stays between normal main memory and CPU.
May be located on CPU chip or module.
Intended to allow access speed approaching register speed.
Used to hold frequently used data
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13. Single cache
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14. Three-level cache
In the figure below shows the use of multiple levels of cache. The L2 cache is slower and typically larger than the L1 cache, and the L3 cache is slower and typically larger than the L2 cache.
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15. Size of Cache Memory
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16. Cache Memory working
When CPU attempts to read a word of data from memory , a check is made in cache , if present deliver to CPU.
If not present, block of memory is read into cache and delivered to CPU.
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17. Elements of cache design
Elements of cache design depends upon the following things:
Logical cache address or Physical cache address, Size of cache design and Replacement Algorithm.
A logical cache, also known as a virtual cache, stores data using virtual addresses. The processor accesses the cache directly, without going through the MMU. A physical cache stores data using main memory physical addresses.
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18. Addresses (Logical & Physical)
Logical Address
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Physical Address

19. Thank you!!!