Computer Memory Units and Memory Types
Computer memory questions often test definitions, order of units and the differences between volatile and non-volatile memory. The supplied resources provide a clear progression from basic units to RAM, ROM, cache and registers.
1. Memory units
| Unit | Equivalent in the supplied notes |
|---|---|
| Bit | 1 binary digit |
| Nibble | 4 bits |
| Byte | 8 bits |
| KB | 1024 bytes |
| MB | 1024 KB |
| GB | 1024 MB |
| TB | 1024 GB |
| PB | 1024 TB |
2. Primary versus secondary memory
The notes describe primary memory as fast, relatively small and directly accessed by the CPU during program execution. Secondary memory is described as slower, larger and intended for persistent storage even when power is off.
3. RAM
RAM is the main primary memory used while programs run. The CPU reads from and writes to RAM, and the data/instructions needed for processing must be loaded into it. The notes classify RAM as volatile.
4. ROM
ROM is presented as permanent primary memory and non-volatile. The source notes connect ROM with BIOS, hardware checking and the start of the booting process. Variants mentioned include PROM, EPROM and EEPROM.
5. Cache memory
Cache is a small, high-speed memory located between the CPU and RAM. It stores frequently used data/instructions to reduce access time. A cache hit means the requested data is found in cache; a cache miss means it must be fetched from RAM.
6. SRAM and DRAM
| Feature | SRAM | DRAM |
|---|---|---|
| Use in source | Cache memory | Main RAM |
| Refreshing | Not constantly refreshed | Needs continuous refreshing |
| Speed | Faster | Slower |
| Cost | More expensive | Cheaper |
| Capacity | Smaller | Larger |
| Volatility | Volatile | Volatile |
7. Registers
Registers are tiny storage elements inside the CPU. The notes describe them as the fastest memory in a computer, with very small capacity, holding data, instructions, addresses or results currently being used by the CPU.