Top 10 List of Week 04

1. Logical and Physical Address
   Logical Address is generated by CPU while a program is running. This address is used as a reference to access the physical memory location by CPU.
   Physical Address identifies a physical location of required data in a memory. The user never directly deals with the physical address but can access by its corresponding logical address.

2. Memory Management Unit
   Memory Management Unit(MMU) is the physical hardware that handles its virtual memory and caching operations. The MMU is usually located within the computer’s CPU, but sometimes operates in a separate integrated chips. All data request inputs are sent to the MMU, which in turn determines whether the data needs to be retrieved from RAM or ROM storage.

3. Paging in Operating System
   Paging is a memory management scheme that eliminates the need for contiguous allocation of physical memory. This scheme permits the physical address space of a process to be non – contiguous. The mapping from virtual to physical address is done by the memory management unit (MMU) which is a hardware device and this mapping is known as paging technique.

4. Random Access Memory (RAM) and Read Only Memory (ROM)
   Computer memory is of two basic type – Primary memory(RAM and ROM) and Secondary memory(hard drive,CD,etc.). Random Access Memory (RAM) is primary-volatile memory and Read Only Memory (ROM) is primary-non-volatile memory.

5. Difference between Byte Addressable Memory and Word Addressable Memory
   When the data space in the cell = 8 bits then the corresponding address is called as Byte Address. When the data space in the cell = word length of CPU then the corresponding address is called as Word Address. You could check the website if you want to know more.

6. Big Endian and Little Endian
   Big Endian Byte Order: The most significant byte (the “big end”) of the data is placed at the byte with the lowest address. The rest of the data is placed in order in the next three bytes in memory.
   Little Endian Byte Order: The least significant byte (the “little end”) of the data is placed at the byte with the lowest address. The rest of the data is placed in order in the next three bytes in memory.

7. Swapping in Operating System
   Swapping is one of the several methods of memory management. In swapping an idle or a blocked process in the main memory is swapped out to the backing store (disk) and the process that is ready for execution in the disk, is swapped in main memory for execution.

8. Segmentation
   Segmentation is the process of separating each process into segments of varying sizes. A segment takes up its own logical address space. In order for the memory to be moved from the logical to physical address space, a segment table holds the addresses; it contains the physical address for the segment and the size of the segment.

9. Multilevel Paging in Operating Systems
   Multilevel Paging is a paging scheme which consist of two or more levels of page tables in a hierarchical manner. It is also known as hierarchical paging. The entries of the level 1 page table are pointers to a level 2 page table and entries of the level 2 page tables are pointers to a level 3 page table and so on. The entries of the last level page table are stores actual frame information. Level 1 contain single page table and address of that table is stored in PTBR (Page Table Base Register).

10. Pointer to Pointer
    A pointer to a pointer is a form of multiple indirection, or a chain of pointers. Normally, a pointer contains the address of a variable. When we define a pointer to a pointer, the first pointer contains the address of the second pointer, which points to the location that contains the actual value.