Dundas Valley Secondary Computer Hardware Types of Memory

Main Memory While the CPU has a small amount of memory on the microprocessor, most of the computer’s memory is located on the motherboard

The Hardware Diagram Where does memory fit into the hardware diagram? Processing Unit Input Devices Output Devices Auxiliary Storage Processing Unit Control Unit ALU Registers ROM RAM Memory Controller

Registers The original Pentium (1993) CPU had 32 registers-each was 8 bytes in size The Pentium 4 (IA-64 core) has 128 integer and 128 floating-point registers plus 64 special function registers. Registers are a small amount of high speed memory built onto the CPU core Registers This is a Pentium 4 core

Internal Cache Level 1 cache (pronounced “cash”) is built into the CPU core It is also called primary cache or internal cache Early processors had 32 KB of L1 cache 512 KB is now common Level 1 cache on a Pentium 4 Cache memory is a scheme to store needed data close to the CPU Cache is used to pre-fetch data and program instructions from main memory

External Cache External cache is often called level 2 (or level 3) cache It is situated on the motherboard close to the CPU It is made of expensive, high-speed memory External cache serves as a stepping-stone between the CPU and RAM L2 cache CPU

RAM Random Access Memory is the largest part of main memory RAM is volatile (contents are destroyed when the power is eliminated) Called “Random Access” because an unit (byte) of memory can be accessed directly without having to search sequentially through memory to find it RAM ICs are housed on small circuit boards called DIMMs or Dual In-line Memory Modules DIMMs are installed into slots on the motherboard

ROM Read-Only Memory stores system programs and data permanently The contents of ROM remain unchanged when the power is turned off The contents of ROM are “burned-in” at the factory and cannot be changed Special types of ROM can be programmed (PROM) or erased (EEPROM) Flash ROM can be reprogrammed quickly without removing it from the circuit board

BIOS The bootstrap program contains the code that starts the computer during a “cold-boot” One of these functions is the POST or Power On Self Test “ROM BIOS” ICs are built on the motherboard The Basic Input-Output System is a type of ROM that holds the computer’s bootstrap program