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The Role of Memory Locations in Program ExecutionMemory Location.pptx
- 1. Addressing methods & machine program sequencing: Memory locations
- 4. Key Characteristic of Computer Memory system
- 6. Main Memory
- 21. Read Operation
- 22. Write Operation
- 27. 1. Direct Mapping Each main memory block maps to only one specific cache line. Simple and fast but can lead to more conflicts. 2. Associative Mapping (Fully Associative) Any block of main memory can go to any line in the cache. Very flexible but slower due to searching entire cache. 3. Set-Associative Mapping Cache is divided into sets, and each set has multiple lines (ways). A block maps to a specific set but can go into any line within that set. Compromise between direct and associative mapping.
- 28. Comparison Table: Feature Direct Mapping Associative Mapping Set-Associative Mapping Flexibility Low High Medium Speed Fast Slow Moderate Hardware Cost Low High Medium Conflict Misses High Low Low to Medium
- 30. Virtual Memory
- 31. Address Space and memory Space
- 32. How It Works • The CPU generates a virtual address (used by the program). • The Memory Management Unit (MMU) translates this into a physical address. • If the data is in RAM it's accessed directly. → • If not in RAM it's in → secondary storage (e.g., hard disk or SSD), and the system: • Loads the data into RAM • May remove some existing data from RAM to make space • This process is called paging or swapping
- 33. Demand Paging Is Used • Only the "active" or "frequently used" parts of a program are loaded into RAM. • The rest are stored in the page file / swap space on the disk (SSD or HDD). • When needed, inactive parts (pages) are brought into RAM. • If RAM is full, some unused pages are swapped out. This is called demand paging.
- 36. Virtual Address Register (20 bits) The CPU generates a virtual address whenever a program accesses memory. This virtual address is stored in the Virtual Address Register. It is 20 bits wide, meaning the program can use up to 220=1,048,5762^{20} = 1,048,576220=1,048,576 memory locations (1 MB addressable space). Memory Mapping Table •This is the core of the translation system. •It takes the virtual address as input and looks up the corresponding physical address. •You can think of it like a dictionary: Virtual Address Physical Address →
- 37. Memory Table Buffer Register After translation, the result (physical address) is temporarily stored in this buffer. This register acts as a bridge between the mapping table and the main memory hardware.4. Main Memory Address Register (15 bits) It receives the 15-bit physical address from the buffer. Since it is 15 bits, it can access up to 215=32,7682 15 =32,768 locations 32 → KB of physical memory. This shows that even if we have a large virtual space (1 MB), the actual physical space is smaller (32 KB).
- 38. Main Memory This is the physical memory (RAM) where data or instructions are stored. The address in the Main Memory Address Register is used to locate the required word in memory.6. Main Memory Buffer Register Once the data is accessed from main memory, it is temporarily held in this register before being sent to the CPU or I/O device.
- 39. CPU generates a 20-bit virtual address The address goes into the memory mapping table. The table converts it into a 15-bit physical address. This address is stored in the main memory address register. Main memory is accessed at this physical address. The data is fetched and placed in the main memory buffer register.
- 40. Advantages of Virtual Memory Efficient use of physical memory Enables multi-tasking Protects memory between processes Lets large programs run even on small RAM systems Disadvantages May cause slower performance if paging happens frequently (called thrashing) Requires additional hardware (MMU)