How to identify the Type of Memory your Computer Needs

If there is insufficient information in your user system manual or if the user manual is not available then the following guide should provide the information you require. You will though, need to remove the cover and identify the sockets where the memory is installed. Your user manual if available, may provide a schematic highlighting the position of these sockets on your motherboard.

Main Types of Memory.  Memory versus CPU Upgrade ?
What Are Banks ?  What Does 4x32 Mean ? 
What Are Nano-Seconds ?  What Does FPM and EDO Mean ? 
How Much Memory Do I Need ? What is a Parity Simm ? 
Memory Need Assessment.  What is the Difference Between High-Density and Low-Density Simms ? 


1. Main Types of Memory

There are three main types of memory and the following information should allow you to identify which type your machine currently has installed :

               30 Pin Simm (Single Inline Memory Module)

30 Pin Memory Simms are approximately 3 inches in length and inch in height. They are generally used on the 386 CPU and older 486 CPU based machines. 3 or 9 Chips on the 30 Pin Simm denotes Parity, 2 or 8 Chips on the 30 Pin Simms denotes non-parity. Generally, you can install parity simms into a system that currently uses non-parity but you cannot install non-parity simms into a system that currently uses parity.

                72 Pin Simm (Single Inline Memory Module)

72 Pin Memory Simms are approximately 4 inches in length 1 inch in height. They are generally used on the newer 486 and the Pentium based machines. 2 or 8 Chips on the 72 Pin Simm denotes Non-Parity, 9 or 12 chips normally denotes Parity but there are 12 chip non-parity simms available. If you are unsure that why not send us an e-mail or give us call to confirm.

There are two flavours of 72 Pin Simms. EDO and FPM. EDO is used on the newer Pentium based systems and FPM is used on the 486 and earlier Pentium based systems. It is not possible by looking at the simm to determine whether it is EDO or FPM. EDO generally gives an additional 10-20% performance improvement but only if your motherboard supports EDO memory.

               168 Pin Dimm (Dual Inline Memory Module)

A 168 Pin Dimm is approximately 5 inches in length and 1 inch in height and contains 84 Pins on either side. It is referred to as a 168 Pin Dimm because it reads both sides of the Dimm simultaneously. The Dimm is different from the Simm in that it has two notches on the contact edge and inserts into the socket straight down, without the need for tilting. Dimm sockets also have release tabs at each end which acts as a lever to push the module up out of the socket during removal.

There are several different flavours of Dimm, including FPM, SDRAM (8,10,12 Megaherz), EDO (Buffered, Non-Buffered, 3.3V & 5V). It is imperative to select the correct type of Dimm module when upgrading.

               Identifying the Number of Simms You Need to Install ?

Now that you have identified the type of memory you have installed, you will need to identify the minimum number of modules you can install. Please refer to the section called "How Much Memory Do I Need" with regard to the amount of memory you require which is dependent on the type of activities you are performing and the operating system.

 What Are Banks ?

Some motherboards use a system that divides the memory slots into banks. Your system may or may not use banks. If your computer has eight 30 Pin Memory slots they are probably banked into 2 banks of four slots. If your system is banked you will need to fill each bank with matching pairs of SIMMS. These banks are usually numbered, such as bank 0 or bank 1.

As a general rule, on a 486 based system, each socket operates as 1 bank, therefore 1 module can be installed at a time. On a Pentium based system that uses 72 Pin Simms, modules must be installed in pairs. Pentium based systems that use Dimms can be installed 1 module at a time.

2. What Are Nano-Seconds ?

Nanoseconds are the basis on which the speed of memory is measured. Most systems require 70NS or faster memory modules. Remember the lower the number the faster the memory, therefore 60NS is faster than 70NS. For most computers it is possible to use two different speed SIMMS as long as you keep them matched in size and speed in the same bank.

3. How Much Memory Do I Need ?

When determining the amount of memory you require you need to consider the optimum memory configuration of your operating system and the applications that you use :

3.1 Operating System

Baselines have been identified for each of the major operating systems. Upgrading to the baseline for your particular operating system is a good place to start. You will then need to consider the applications you are using.

Recent tests on Windows 95 show significant improvement in Windows 95 performance at 32MB and beyond. Recent tests on Windows NT shows performance improvements of between 30-40% at 32MB and up to 63% improvement at 64MB.

3.2 Applications

Different people use different applications in different ways. Some will use all the features available whilst others will only certain aspects. An easy rule of thumb is to identify the size of the files you are using and allow for between 3 and 5 times that size in RAM. For Example, if the files you are using are typically 2MB in size then you should allow between 6MB and 10MB of memory.

3.3 Memory Need Assessment.

The following guidelines should be used to identify the type of applications that you use in conjuction with your operating system in order to determine the amount of memory you require. As previously mentioned, baseline memory configurations have been identified for the majority of operating systems and are a good place to start when determining the amount of memory you require.

Windows 95/98 Windows 3.1 Windows NT OS/2 Mac O/S
Baseline 16-32MB 12-24MB 32-48MB 16-32MB 12-24MB
Light 16-48MB 12-48MB 32-64MB 16-48MB 12-48MB
Medium 32-96MB 24-64MB 32-96MB 32-96MB 24-64MB
Heavy 64-256MB 48-256MB 64-256MB 64-256MB 48-256MB

Light : Word Processing, E-mail, Data Entry, Spreadsheets, Network Connectivity, Fax, accounting.

Medium : Databases, Complex Presentations, Project Mgmt, Internet Access, Video Conferencing, Statistical applications.

Heavy :  2D CAD, 3D CAD, Animation, Complex photo-editing, Multimedia Presentations, Web Development, Animation, Solid Modeling.

4. Memory versus CPU Upgrade ?

Upgrading your memory will give significant improvements in performance versus a CPU upgrade and is normally cheaper and easier to perform. A Pentium 100 with 32MB of memory actually outperforms a Pentium Pro 200 with 16MB of memory.

System performance improves up to 44% at 32MB main memory and up to 63% at 64MB.

5. What Does 4x32 Mean ?

30 pin Parity simms are often referred as 1MB-1x9, 4MB-4x9 and 72 Pin non-parity Simms are often referred as 4MB-1x32, 8MB-2x32 and 72 Pin Parity Simms are often referred as 4MB-1x36, 8MB-2x36. The "1x32" part is the simm specification, also referred to as architecture, because it indicates the simm design in terms of number of chips and density of those chips. If you multiply the 2 numbers out, (E.G 1x32) you get the total number of megabits and then if you divide by 8 (for non-parity) and 9 (Parity) to get the size in megabytes.

6. What Does FPM and EDO Mean ?

FPM (Fast Page Mode) and EDO (Enhanced Data out) are the two types of DRAM chips used on 30 Pin simms, 72 Pin simms and certain 168 Pin Dimms. EDO based DRAM chips were designed to accommodate the faster processors and are normally found in systems with a Pentium 100MHZ processor or faster.

7. What is a Parity Simm ?

Parity Simms are usually required on older type motherboards present in 386 or older 486 based systems. They are often referred to as 4x9 (4MB-30 Pin), 1x36 (4MB-72 Pin), 2x36 (8MB-72 Pin) etc. This type of memory sends an extra data bit to check for errors in transmission, making a total of nine bits instead of eight. With new technology and better quality motherboards, these error detection bits are no longer required.

9. What is the Difference Between High-Density and Low-Density Simms ?

A high-density SIMM is one which has been designed with 64Mbit DRAM chips and a low-density chip is one which has been designed with 16Mbit DRAM chips. A SIMM designed with 64Mbit chips will have fewer chips than a SIMM designed with 16Mbit DRAM chips.