Computer Memory and Architecture

RAM and ROM

Types of RAM

• SRAM (Static RAM): uses transistors to store data, faster and more expensive than DRAM
• DRAM (Dynamic RAM): uses capacitors to store data, slower and less expensive than SRAM
• DDR RAM (Double Data Rate RAM): transfers data on both rising and falling edges of clock signal, increasing bandwidth

ROM Chips

• PROM (Programmable ROM): can be programmed once by the user
• EPROM (Erasable Programmable ROM): can be erased and reprogrammed
• EEPROM (Electrically Erasable Programmable ROM): can be erased and reprogrammed electrically
• Flash ROM: a type of EEPROM, used in solid-state drives and memory cards

Computer Architecture

• Von Neumann Architecture: uses a single bus for instruction and data, has a program counter, and an arithmetic logic unit (ALU)
• Harvard Architecture: uses separate buses for instruction and data, has a program counter, and an ALU

Memory Hierarchy

• Level 1 Cache (L1 Cache): small, fast cache built into the CPU
• Level 2 Cache (L2 Cache): larger, slower cache outside the CPU
• Main Memory (RAM): slower and larger than cache
• Secondary Storage (Hard Drive): slowest and largest

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 Lines: blocks of data brought into the cache from main memory

Difference between RAM and ROM

• RAM (Random Access Memory): volatile, loses data when power is off, used to store data temporarily
• ROM (Read-Only Memory): non-volatile, retains data even when power is off, used to store permanent data
• Key difference: RAM is writable and volatile, while ROM is not writable and non-volatile