Addressable Memory
- Main memory is address using a unique memory location
- This is called the main memory address
- Like a house number on a street
- This is called the main memory address
- The size of a memory location is typically 1 Byte
- There are some computer systems that are word addressable
- I.E. each memory location is the size of the word length
- There are some computer systems that are word addressable
- The memory address is dependent on the bit architecture of the
processor
- This is why 32-bit processors could only address up to 4GB of system memory
- All three components of the system bus are used when addressing main
memory
- The system bus is shared, but a particular memory address gains exclusive access at a particular time
Addressing Memory
- Memory is conceptually represented as cells
- Each cell contains one or more bits (dependant on architecture)
- Each bit is a representation of there being a charge, or not
- Consumer computers use byte-addressable memory
- Each memory cell stores 1 bit
- These are grouped into WORDS (2 bytes, 16 bits), linked to the memory interface
- Byte addressable memory refers to architectures where data can be accessed and addressed in units that are narrower than the bus
- In modern CPU’s an address refers to byte, that is 8 bits
- The memory address is itself a bit pattern and the number of bits allows for differing memory addresses
- 32 vs 64 Bit Address
- Older computer architecture using 32-bit memory addresses were vastly limited in how much ‘addressable memory’ they could access
- If you had an old computer, you were limited to under 4GB of RAM
- 32-bit addresses range from 0 to 4,294,967,296
- Newer 64-bit architecture allows you to individually address up to 16 exabytes
- Older computer architecture using 32-bit memory addresses were vastly limited in how much ‘addressable memory’ they could access