Computer Memory Types and Hierarchy

Computer Memory

Types of RAM

• SRAM (Static RAM): Fast, expensive, and volatile (loses data when power is turned off).
• DRAM (Dynamic RAM): Slower, cheaper, and volatile (loses data when power is turned off).
• ECC RAM (Error-Correcting Code RAM): A type of RAM that includes an extra chip to detect and correct data errors.
• SO-DIMM (Small Outline Dual In-Line Memory Module): A type of RAM used in laptops.

ROM Types

• PROM (Programmable ROM): Can be programmed once by the user.
• EPROM (Erasable Programmable ROM): Can be erased and reprogrammed multiple times.
• EEPROM (Electrically Erasable Programmable ROM): Can be erased and reprogrammed electrically.
• Flash ROM: A type of EEPROM that can be erased and reprogrammed in blocks.

Memory Hierarchy

• Level 1 Cache (L1 Cache): Smallest and fastest cache, built into the CPU.
• Level 2 Cache (L2 Cache): Larger and slower than L1 cache, but still relatively fast.
• Main Memory (RAM): The largest and slowest memory type.
• Secondary Storage (Hard Disk): The slowest and largest storage type.

Cache Memory

• Cache Hit: When the CPU finds the required data in the cache.
• Cache Miss: When the CPU does not find the required data in the cache.
• Cache Line: The unit of data transferred between the cache and main memory.
• Cache Replacement Policy: The strategy used to decide which cache line to replace when the cache is full.