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• 1. Microprocessor and Memory Basics
• What is a microprocessor and where are they used?
• Abstract system architecture
• System communication
  • Data bus, address bus, control bus
  • Reading data from memory
  • Writing data to memory
  • The Address Capacity of Memory
• Inside the microprocessor
  • The Arithmetic and Logic Unit
  • The Program Counter
  • Registers
• Inside memory
  • Memory Read and Write Operations
  • Calculating storage space
  • Address decoders
  • Tri-state buffers
  • Multiple memory chips
  • Other types of memory
  • Memory mapped input/output

The Address Capacity of Memory

Let a = number of address wires and d = number of data wires. a is the width of the address bus, while d is the width of the data bus.

In many older computers, the address bus was 16 bits wide (a = 16). This meant that there were 16 wires. Such microprocessors could address up to 2¹⁶ = 65536 memory locations. By increasing the width of the address bus, more memory locations can be directly addressed. Each time the width is increased by one wire, the address capacity is doubled. ARM processors normally have 32-bit wide address buses. A 32-bit ARM processor could address up to 2³² = 4,294,967,296 memory locations!

In older computers, the data bus was a mere 8 bits wide (d=8). Each location was an 8-bit byte. Each byte (8 bits) could store either an unsigned number in the range 0-255 or a 2's-complement signed number in the range -128 to 127. By increasing the number of data wires by one, the capacity goes up by 2^a bits.

ARM processors have 32-bit wide data buses. Each location is a word which is 4 bytes or 32 bits long. Each word could store either an unsigned number in the range 0-4294967295 or a 2's-complement signed number in the range -2,147,483,648 (-2³¹) to 2,147,483,647 (2³¹-1).

The total addressed capacity in bytes is: 2^a

For an ARM processor, the addressable capacity is 2³² bytes (or 4 Gigabytes of memory!)