Computer Memory Hierarchy and Characteristics

A computer is used to store data in memory and we have found that there are a large variety of storage devices available for storing data in the computer system. the primary reason is the cost per byte of storage and access time of the memory. and it also depends that whether storage is volatile or not.

In a computer, the memory system is organized as a hierarchy consisting of a number of levels. at the top of the level, the computer uses cache memory that has high speed, low capacity, and volatile memory. and at the bottom level computer uses the high speed, slow access, and nonvolatile memory to store the data.

Another thing is that the semiconductor memories that use high-speed transistor flip flops also known as cache memories are the most expensive and also work in the fast mode. you can see the capacity, access time, and cost per byte for the memories shown below.

• Average capacity – 16 MB
• Technology – High-speed integrated circuits
• 0.5 ns average time to access a byte
• Instructions and data to be immediately used
• 10 units cost per byte

• Average capacity – 512 MB
• Technology – Integrated circuits(DRAM)
• 5 ns average time to access a byte
• Used by the programs and data
• 1 unit cost per byte

• Average capacity – 750 MB
• Technology – Magnetic surfaces on the hard disk
• 8 ms average time to access a byte
• Used for large data files and for program overflow from main memory
• 1/100 units cost per byte

• Average capacity – 32 GB
• Technology – Integrated circuit
• 1 us average time to access a byte
• used to store personal programs and data files and backup data files
• 1/1000 units cost per byte

• Average capacity – 6.25 TB
• Technology – Long 1/2” tape wound on cartridge
• Used to store history files and backup for the disk. data program exchange between installations.
• 1/1000 units cost per byte

• Average capacity – 600MB
• Technology – Laser disk
• 500 ms average time to access a byte
• Used to store video files
• 1/100000 units cost per byte

• Average capacity – 50 G
• Technology – Laser disk
• 500 ms average time to access a byte
• Used to store video files
• 1/10000 units cost per byte

To get the best result in terms of storage we need to use a combination of all these types of storage devices. cache memory is used to store the data that needs to be accessed immediately. and the random access memory is used to store the programs that currently executing. the files that need in the future stored in the disk. and the magnetic tape storage device is used to store the data that is used rarely.

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