CP1610: Introduction to Computer Components Primary Memory

What is Memory? Memory is used to:  Store data;  Store commands (instructions);  Store system settings;

Computer Memory Three categories of memory devices:  Primary Memory;  Secondary Memory;  Archival Storage Devices;

What is Primary Memory? Also called system memory. Essential for computer to operate. Stores data and commands to be used by the CPU. Stores basic system settings. Two main types:  RAM  ROM

RAM vs. ROM RAM  Random Access Memory  Stores data and instructions  Volatile Examples:  RAM chips  CMOS ROM  Read Only Memory  Stores basic system settings  Non-volatile Example:  BIOS

The Primary Memory Hierarchy

Notes in your locker, car, or at home, are too far away! Retrieving Data from Secondary Storage RAM: The book on your desk is much closer! Cache: The papers in your hand are the next ones you will use!

RAM on the Motherboard Static RAM (SRAM)  Very fast;  Expensive;  Does not need to be refreshed;  Used as Cache;  On Chip, Coast Card, or inside CPU; Dynamic RAM (DRAM)  Slow;  Cheaper;  Needs constant refreshing;  Used as RAM;  SIMMs, DIMMs and RIMMs

Different Types of DRAM SIMM  Single Inline Memory Module DIMM  Dual Inline Memory Module RIMM  Rambus Inline Memory Module

Installing a SIMM Chip

Installing a DIMM Chip

Installing a RIMM Chip

Older Types of RAM Conventional RAM Fast Page Memory (FPM) Extended Data Out (EDO) RAM Burst EDO (BEDO) RAM

Newer Types of RAM Sychronous DRAM (SDRAM)  Synced with system clock Double Data Rate (DDR) SDRAM  Most popular today  184-pin DIMMs  200-pin SODIMMs Rambus DRAM (RDRAM)  Not as common  Faster system bus  RIMMs

Cache Memory Very fast SRAM Used to store the very next command or data needed by the CPU Three Types:  L1  L2  L3

Error Correction Method used to:  Detect integrity of data stored in RAM  Ensure memory is complete  Prevent data corruption or loss Non-Error Correcting Memory:  Used in older systems to speed up memory;

Types of Error Correction Parity:  Older;  Cannot correct data corruption; Error Correcting Code (ECC):  Newer;  Most widely used;  Can correct data corruption;

How Parity Works

System Memory Conventional Memory:  First 1 MB of memory;  Used to run programs and store system drivers; High Memory (Hi-Mem):  About 64 KB of memory just above the 1 MB point; Extended and Expanded Memory:  Anything above 1 MB;  Systems must run in ‘Protected Mode’ to use;

Available to the user for any software Reserved for device drivers and system functions Anything above 1 MB