Some definitions - buses, word size, main memory, program counter, operating system

Buses

• Electrical conduits running throughout a computer system that transfer bytes back and forth.
• They are typically designed to transfer fixed-size chunks of bytes known as words.

Word size

• Fundamental system parameter
• Generally, they are either 4-byte (32-bit) or 8-byte (64-bit). 32-bit systems have 32 bit word sizes
• Size of a CPU register
• It also indicates the nominal size of a pointer

Impact of word size on size of virtual address space

• Since the virtual address space is encoded by such words, the maximum size of the virtual address space.
• For a $w$-bit word size, the virtual addresses can range from 0 to $2^w-1$, giving the program access to $2^w$ bytes.
  • For example, for a 32-bit system , the word size is 32 bit. Therefore, the maximum size of the virtual memory can be $2^{32}\text{bytes}=4\text{GB}$

Main memory

• Temporary storage that holds both the program code and the data it works on.
• Consists of a collection of dynamic random access memory (DRAM) chips.
• Logically, memory is organized as an array of bytes, each with its own unique address (array index) starting at 0.

Program counter (PC)

• Special register that points at some machine instruction in main memory
• Processor executes the instruction pointed at by the PC and updates the PC to point to the next instruction

Attachments

Sources

• Computer Systems - A Programmer’s Perspective

Related Notes