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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

Multiple memory chips

The days when a desktop computer only needed 32K for its operating system are sadly long gone. Even a memory chip that can store 1 megabyte will not provide enough storage for the microprocessor on its own.

Our memory chip with its 20 address wires contains 2²⁰ locations. If the chip has 8 data lines, then each location can hold a byte. A typical ARM microprocessor has 32 address wires in total, so it can address up to 2³² locations. To completely fill the ARM microprocessor address space with these memory chips you would need:

2³² / 2²⁰ = 2¹² = 4096 chips (4 Gigabytes)

(Some top-end Pentium desktops are now being sold with 1 GB of memory as standard, so physical memory is catching up with 32-bit address spaces.)

The ARM address space is from 00000000_H to FFFFFFFF_H. A single 1 megabyte memory chip contains 2²⁰ = 100000_H.

Therefore we need to wire one memory chip such that it responds to addresses 00000000_H to 000FFFFF_H and the next chip so it responds to addresses 00100000_H to 001FFFFF_H and so on.