Memory hierarchy
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The document discusses memory hierarchy as a solution for modern computing. It describes Moore's Laws of increasing transistor density and chip fabrication costs over time. An ideal memory would have zero access time, infinite capacity and bandwidth, and zero cost, but real memories involve tradeoffs between speed, size, quality, and cost. A memory hierarchy organizes memory into different levels from fastest and smallest (registers) to slowest and largest (disks). Virtual memory allows computers to use disk storage like memory using page files. Offline and portable memories refer to removable secondary storage media.
Memory hierarchy
- 1. MEMORY HIERARCHY A SOLUTION FOR MODERN DAY COMPUTING
- 2. MEMORY: “The Impression, Reminiscence and Souvenir of an existence, is called Memory.” Or “The ability to collect and recollect data, is called Memory.”
- 3. MOORE’S FIRST LAW: “The number of transistors per square inch on a dense integrated circuit doubles every two years.”
- 4. ROCK’S LAW (MOORE’S SECOND LAW): “The cost of a semiconductor chip fabrication plant doubles every four years.”
- 5. THE PARADOX OF MEMORY: The Ideal Memory: Zero Access Time Infinite Capacity Zero Cost Infinite Bandwidth Realistic Memory: Faster = Expensive Bigger = Slower Quality = Expensive Higher Frequency = More Ports = Expensive
- 6. MEMORY HIERARCHY: At any given time, data is copied between only two adjacent levels: – Upper level: In the direct access to processor. (Smaller, faster, uses more expensive technology) – Lower level: In the indirect access to processor. (Bigger, slower, uses less expensive technology)
- 7. IMPACT OF MEMORY HIERARCHY For Computer Processing: If it worked for Cars: •3,00,000 mph •20,00,000 mpg •4.19 Rupees per Car •3,500x Performance •90,000x Energy efficient •60,000x Lower cost
- 8. LEVELS OF MEMORY HIERARCHY:
- 9. HIERARCHY MANAGEMENT: Registers <-> Memory by compiler Cache <-> Memory by the hardware (CPU) Memory <-> Disks by the Hardware (RAM) and OS Virtual Memory by the Operating System (OS) and Program
- 10. PRIMARY MEMORY: “The upper level volatile memory, directly accessed by processor, is called Primary Memory.” Example: Cache & RAM SECONDARY MEMORY: “The lower level non- volatile memory, indirectly accessed by processor, is called Secondary Memory.” Example: ROM & USB Flash
- 11. VIRTUAL MEMORY: Virtual memory is a feature of an operating system (OS) that allows a computer to compensate for shortages of physical memory by temporarily transferring pages of data from random access memory (RAM) to disk storage. That Portion of disk storage is referred as Virtual Memory or Paging Files.
- 12. NEED FOR VIRTUAL MEMORY: 1. Before the development of the virtual memory technique, programmers in the 1940s and 1950s had to manage directly two-level storage such as main memory or RAM and secondary memory in the form of hard disks or earlier, magnetic drums. 2. Enlarge the address space, the set of addresses a program can utilize. 3. Virtual memory might contain twice as many addresses as main memory.
- 13. VIRTUAL MEMORY (PAGING) Page table Address Space Page table Address Space Physical Memory
- 14. WHAT IS OFFLINE MEMORY? The term offline memory is referred to a secondary storage medium that is non-volatile and whose data cannot be accessed by the computer once removed. It must be physically inserted into a system every time a users wants to access or edit data. Offline storage can be any type of internal or external storage that can easily be removed from the computer.
- 15. PORTABLE MEMORY Any offline storage that is removable and needs to be plugged in to read/write data and plugged out without effecting any fundamentals of the machine, is called portable memory. Portable memory plays a vital role in the data transfer and specially in making backups for privacy or security concerns. Examples of portable memory are USB drive, SD Cards, Floppy disks, Tape drives and CDs/DVDs or Blu-ray.