Unit-5
Memory Hierarchy Design and Its Characteristics
In the Computer System Design, the Memory Hierarchy is an enhancement to organize
the memory such that it can minimize the access time.
The Memory Hierarchy was developed based on a program behavior known as locality of
references (same data or nearby data is likely to be accessed again and again).
Why Memory Hierarchy is Required in the System?
Memory Hierarchy helps in optimizing the memory available in the computer. There are
multiple levels present in the memory, each one having a different size, different cost, etc. Some
types of memory like cache, and main memory are faster as compared to other types of
memory but they are having a little less size and are also costly whereas some memory has a
little higher storage value, but they are a little slower. Accessing of data is not similar in all types
of memory, some have faster access whereas some have slower access.
Types of Memory Hierarchy
This Memory Hierarchy Design is divided into 2 main types:
External Memory or Secondary Memory: Comprising of Magnetic Disk, Optical Disk,
and Magnetic Tape i.e. peripheral storage devices which are accessible by the processor
via an I/O Module.
Internal Memory or Primary Memory: Comprising of Main Memory, Cache Memory
& CPU registers. This is directly accessible by the processor.
,Memory Hierarchy Design
1. Registers
Registers are small, high-speed memory units located in the CPU. They are used to store the
most frequently used data and instructions. Registers have the fastest access time and the
smallest storage capacity, typically ranging from 16 to 64 bits.
2. Cache Memory
Cache memory is a small, fast memory unit located close to the CPU. It stores frequently used
data and instructions that have been recently accessed from the main memory. Cache
memory is designed to minimize the time it takes to access data by providing the CPU with
quick access to frequently used data.
3. Main Memory
Main memory, also known as RAM (Random Access Memory), is the primary memory of a
computer system. It has a larger storage capacity than cache memory, but it is slower. Main
memory is used to store data and instructions that are currently in use by the CPU.
Types of Main Memory
Static RAM: Static RAM stores the binary information in flip flops and information
remains valid until power is supplied. Static RAM has a faster access time and is used in
implementing cache memory.
Dynamic RAM: It stores the binary information as a charge on the capacitor. It requires
refreshing circuitry to maintain the charge on the capacitors after a few milliseconds. It
contains more memory cells per unit area as compared to SRAM.
read more about - Different Types of RAM (Random Access Memory)
4. Secondary Storage
Secondary storage, such as hard disk drives (HDD) and solid-state drives (SSD) , is a non-volatile
memory unit that has a larger storage capacity than main memory. It is used to store data and
instructions that are not currently in use by the CPU. Secondary storage has the slowest access
time and is typically the least expensive type of memory in the memory hierarchy.
5. Magnetic Disk
, Magnetic Disks are simply circular plates that are fabricated with either a metal or a plastic or a
magnetized material. The Magnetic disks work at a high speed inside the computer and these
are frequently used.
6. Magnetic Tape
Magnetic Tape is simply a magnetic recording device that is covered with a plastic
film. Magnetic Tape is generally used for the backup of data. In the case of a magnetic tape, the
access time for a computer is a little slower and therefore, it requires some amount of time for
accessing the strip.
Characteristics of Memory Hierarchy
Capacity: It is the global volume of information the memory can store. As we move from
top to bottom in the Hierarchy, the capacity increases.
Access Time: It is the time interval between the read/write request and the availability
of the data. As we move from top to bottom in the Hierarchy, the access time increases.
Performance: The Memory Hierarch design ensures that frequently accessed data is
stored in faster memory to improve system performance.
Advantages of Memory Hierarchy
Performance: Frequently used data is stored in faster memory (like cache), reducing
access time and improving overall system performance.
Cost Efficiency: By combining small, fast memory (like registers and cache) with larger,
slower memory (like RAM and HDD), the system achieves a balance between cost and
performance. It saves the consumer's price and time.
Optimized Resource Utilization: Combines the benefits of small, fast memory and large,
cost-effective storage to maximize system performance.
Efficient Data Management: Frequently accessed data is kept closer to the CPU, while
less frequently used data is stored in larger, slower memory, ensuring efficient data
handling.
Memory Hierarchy Design and Its Characteristics
In the Computer System Design, the Memory Hierarchy is an enhancement to organize
the memory such that it can minimize the access time.
The Memory Hierarchy was developed based on a program behavior known as locality of
references (same data or nearby data is likely to be accessed again and again).
Why Memory Hierarchy is Required in the System?
Memory Hierarchy helps in optimizing the memory available in the computer. There are
multiple levels present in the memory, each one having a different size, different cost, etc. Some
types of memory like cache, and main memory are faster as compared to other types of
memory but they are having a little less size and are also costly whereas some memory has a
little higher storage value, but they are a little slower. Accessing of data is not similar in all types
of memory, some have faster access whereas some have slower access.
Types of Memory Hierarchy
This Memory Hierarchy Design is divided into 2 main types:
External Memory or Secondary Memory: Comprising of Magnetic Disk, Optical Disk,
and Magnetic Tape i.e. peripheral storage devices which are accessible by the processor
via an I/O Module.
Internal Memory or Primary Memory: Comprising of Main Memory, Cache Memory
& CPU registers. This is directly accessible by the processor.
,Memory Hierarchy Design
1. Registers
Registers are small, high-speed memory units located in the CPU. They are used to store the
most frequently used data and instructions. Registers have the fastest access time and the
smallest storage capacity, typically ranging from 16 to 64 bits.
2. Cache Memory
Cache memory is a small, fast memory unit located close to the CPU. It stores frequently used
data and instructions that have been recently accessed from the main memory. Cache
memory is designed to minimize the time it takes to access data by providing the CPU with
quick access to frequently used data.
3. Main Memory
Main memory, also known as RAM (Random Access Memory), is the primary memory of a
computer system. It has a larger storage capacity than cache memory, but it is slower. Main
memory is used to store data and instructions that are currently in use by the CPU.
Types of Main Memory
Static RAM: Static RAM stores the binary information in flip flops and information
remains valid until power is supplied. Static RAM has a faster access time and is used in
implementing cache memory.
Dynamic RAM: It stores the binary information as a charge on the capacitor. It requires
refreshing circuitry to maintain the charge on the capacitors after a few milliseconds. It
contains more memory cells per unit area as compared to SRAM.
read more about - Different Types of RAM (Random Access Memory)
4. Secondary Storage
Secondary storage, such as hard disk drives (HDD) and solid-state drives (SSD) , is a non-volatile
memory unit that has a larger storage capacity than main memory. It is used to store data and
instructions that are not currently in use by the CPU. Secondary storage has the slowest access
time and is typically the least expensive type of memory in the memory hierarchy.
5. Magnetic Disk
, Magnetic Disks are simply circular plates that are fabricated with either a metal or a plastic or a
magnetized material. The Magnetic disks work at a high speed inside the computer and these
are frequently used.
6. Magnetic Tape
Magnetic Tape is simply a magnetic recording device that is covered with a plastic
film. Magnetic Tape is generally used for the backup of data. In the case of a magnetic tape, the
access time for a computer is a little slower and therefore, it requires some amount of time for
accessing the strip.
Characteristics of Memory Hierarchy
Capacity: It is the global volume of information the memory can store. As we move from
top to bottom in the Hierarchy, the capacity increases.
Access Time: It is the time interval between the read/write request and the availability
of the data. As we move from top to bottom in the Hierarchy, the access time increases.
Performance: The Memory Hierarch design ensures that frequently accessed data is
stored in faster memory to improve system performance.
Advantages of Memory Hierarchy
Performance: Frequently used data is stored in faster memory (like cache), reducing
access time and improving overall system performance.
Cost Efficiency: By combining small, fast memory (like registers and cache) with larger,
slower memory (like RAM and HDD), the system achieves a balance between cost and
performance. It saves the consumer's price and time.
Optimized Resource Utilization: Combines the benefits of small, fast memory and large,
cost-effective storage to maximize system performance.
Efficient Data Management: Frequently accessed data is kept closer to the CPU, while
less frequently used data is stored in larger, slower memory, ensuring efficient data
handling.
