Understanding, Identifying and Upgrading the RAM in your PC

Introduction

This tutorial is intended to explain what RAM is and give some background on different memory technologies in order to help you identify the RAM in your PC. It will also discuss RAM speed and timing parameters to help you understand the specifications often quoted on vendors' websites. Its final aim is to assist you in upgrading your system by suggesting some tools and strategies to help you choose new RAM.

Like all PC components, RAM has gone through a number of evolutionary changes (and some revolutionary changes) and only the RAM designed for your computer will work in your computer. There are literally hundreds of different RAM products on the market today so it is important to know the correct type for your system. I am attempting to write this for the non-technical user but the further I get the more I descend into techno-babble so you may need to learn a few terms along the way. I'll assume familiarity with common terms like Megabytes and Gigabytes etc. Finally I should say I'm not a memory expert, some of the information here I came across in the process of writing this tutorial, but I hope you will get as much out of this exploration of RAM as I have

What is RAM?

Memory, better known as Random Access Memory (RAM) is a set of chips used to store information. These chips can only store information as long as there is electrical power. When the power is turned off, they 'forget' everything and all data is lost. This is because the RAM uses the electricity to store the information. When the electricity dies, so does your data.

Memory Types

Read-Only Memory

• BIOS
• CMOS

Erasable / Programmable Read-Only Memory (EPROM/EEPROM) 

DRAM - Dynamic Random Access Memory - Needs Refresh 

• FPM - Fast Page Memory
• EDO - Extended Data Out
• DDR - Dual Data Rate (DDR2, DDR3, DDR4, DDR5)

SDRAM - Synchronous Dynamic Random Access Memory (DIMMs) 

• PC66 @ 66 Mhz or 100 Mhz 
• PC100 @ 125 Mhz 
• PC133 @ 133 Mhz or 143 Mhz

DDR SDRAM - Double / Dual Data Rate SDRAM (DIMMs)

• DDR200 / PC1600 @ 100 Mhz
• DDR266 / PC2100 @ 133 Mhz
• DDR333 / PC2700 @ 166 Mhz
• DDR400 / PC3200 @ 200 Mhz
• DDR433 / PC3500 @ 217 Mhz
• DDR466 / PC3700 @ 233 Mhz
• DDR500 / PC4000 @ 250 Mhz
• DDR 550 / PC4400 @ 275 Mhz
• DDR 600 / PC4800 @ 300 Mhz

DDR2 / PC2

• DDR2 - 400 / PC2 - 3200 @ 100 Mhz
• DDR2 - 533 / PC2 - 4200 @ 133 Mhz
• DDR2 - 667 / PC2 - 5300 @ 166 Mhz
• DDR2 - 800 / PC2 - 6400 @ 200 Mhz
• DDR2 - 1000 / PC2 - 8000 @ 250 Mhz

DDR3 / PC3

• DDR3 - 800 / PC3 - 6400 @ 100 Mhz
• DDR3 - 1066 / PC3 - 8500 @ 133 Mhz
• DDR3 - 1333 / PC3 - 10667 @ 166 Mhz
• DDR3 - 1600 / PC3 - 12800 @ 200 Mhz
• DDR3 - 1866 / PC3 - 14900 @ 250 Mhz
• DDR3 - 1866 / PC3 - 15000 @ ??? Mhz
• DDR3 - 2133 / PC3 - 17000 @ ??? Mhz

DDR4
SRAM - Static Random Access Memory

No Refresh

Used in Cache Memory (L1 Cache, L2 Cache, L3 Cache)

RDRAM - RAMBUS Dynamic Random Access Memory (RIMM)

16-bit

• RIMM 1600 / PC800 @ 400 Mhz
• RIMM2100 / PC1066 @ 533 Mhz
• RIMM2400 / PC1200 @ 600 Mhz

32-bit RDRAM

• RIMM3200 / PC 800 @ 400 Mhz
• RIMM4200 / PC1066 @ 533 Mhz
• RIMM4800 / PC1200 @ 600 Mhz

RAM / Memory Form Factors

Desktop, Workstation and Server RAM / Memory Form 

1. SIMMS - Single In-line Memory Module (obsolete)

Pinouts:

• 30-pin (8 bits + 1 parity bit)
• 72-pin (32 bits plus optional 4 parity bits)
• Types Supported
• Fast Page Mode (FPM) DRAM
• Extended Data Out (EDO) DRAM

2. DIMMS - Dual Inline Memory Module

Pinouts

• 168-pin SDRAM
• 184-pin DDR SDRAM
• 240-pin DDR2 SDRAM

3. RIMM - "RAMBUS" Inline Memory Module

Pinouts

• 184-pin
• 232-pin

Laptop RAM / Memory Form Factors

Micro DIMM

• 144-pin
• 172-pin
• 214-pin

SO-DIMM - Small Outline DIMM

• 72-pin
• 144-pin
• 200-pin
• 204-pin

Different Types of Memory and some Terminology

In "the beginning" RAM came in the form of semiconductor chips which were individually plugged, or soldered, into the motherboard. That made up the original 640KB of system memory that DOS hung onto for so long. Now memory comes in clip-in modules, usually called memory sticks (not to be confused with USB Flash drives which sometimes go by that name). Memory sticks or modules have changed format over the years as their capacity has increased. Here is a list of the main types, in rough order of increasing complexity, along with other terms used to describe them:

A 30 pin SIP module

A 30pin SIMM module

A DIMM module *

A DDR module with heat spreaders *

A DDR2 module with large heat spreaders *