Von Neumann model - Memory Memory is an array of Cells. Memory keeps information in the cells. Each Cell has a unique address and could be selected by its Address. Information could be loaded from Memory Cell to Register or stored from Register to Memory Cell. The source of information in this case is not changed. Only the destination is overwritten.

Memory example 4 cells In this example: The memory contains 4 Cells. They are addressed by 2 bit address which is enough to select all 4 Cells. If the memory is larger, then the address bits have to be more to be able to address more Cells.

Memory example 8 cells, 8 bits Address length is 3 bits Memory Cell length is 8 bits (1 byte) We can load or store 8 bits at once.   3 address bits address 23 = 8 Memory Cells. Data and Address registers lengths do not depend each of other.

Memory example 8 cells, 16 bits Address length is 3 bits Memory Cell length is 16 bits (2 bytes) We can load or store 16 bits at once.   3 address bits address 23 = 8 Memory Cells. Data and Address registers lengths do not depend each of other.

MIPS model 232 cells, each 8 bits MIPS memory is an array of 232 bytes. Each byte has a 32-bit address. Each byte can hold an 8-bit pattern, one of the 256 possible 8-bit patterns. The addresses of MIPS main memory range from 0x00000000 to 0xFFFFFFFF. 232 bytes Memory Size Operations Load: a bit pattern starting at a designated address in memory is copied into a register inside the processor. Store: a bit pattern is copied from a processor register to memory at a designated address. Address 32 bits General Purpose Register

MIPS memory layout The lower half (most of it anyway) is for user programs. User memory is further divided (by software convention) into text, data and stack segments. Text Segment: This holds the machine language of the user program (called the text). Data Segment: This holds the data that the program operates on. Static Data Dynamic Data Stack Segment: With high level languages, local variables and parameters are pushed and popped on the stack as procedures are activated and deactivated. ROM, Device buffers, … not available for user programs Dynamic Data Dynamic Data Static Data User program machine code User programs and data are restricted to the last 231 bytes. The last half of the address space is used for specialized purposes. OS Kernel