G3 RAM - upgrade
Remarks on the usage of SDRAM in Power Macintosh G3 Computers

Christof Klaiber

June 19, 1998, revised November 15, 2000

The now called Old World Apple Power Macintosh G3 models come with the Gossamer Logic Board.¹ They support SDRAM in three 168-pin DIMM slots. Because these models do read the SPD-EEPROM (Serial Presence Detect Electrical Erasable Programmable Read Only Memory) on the DIMM, the PROM is required and must be set properly according to [2] and [3]. Many (if not all) IBM-compatibles do not read the SPD-EEPROM, therefor some manufacturers don't put this part on on their DIMMS. Others do provide an appropriate EEPROM, which is not programmed properly though. Where the first can be easily determined (in most cases it's a tiny 8-pin package labeled 24C02 or similar), the latters may only be found out by trial and error. Due to many sellers restricting the warranties to Integrated Circuits this may become an expensive adventure.

The intention in writing this is to provide you with the information, I have, so you may be able to distinguish compatible and incompatible parts, before you have to buy them. It is always a good idea to ask your dealer if he would take back the parts, if they are not working with your computer, but most dealers won't do that, because RAM is a highly ESD - sensitive (ElectroStatic Discharge) device and you can never be sure, if and how long it will work after it has become familiar with some kind of electrical dischargement.

According to [1], table 1 lists the parts that work properly with the Power Macintosh G3 models. [5] gives a list of vendors that build compatible DIMMs (table 2) and a list of vendors that build incompatible ones (table 3).² My own RAM-Configuration is listed in table 4.

Table 1: Compatible SDRAM DIMMs for the Power Macintosh G3 computer

Vendor Name	SDRAM DIMM part number
Hyundai	HY57V168010A TC-10, HYM7V64400TFG-10
LG Semicon	GM72V1681BT 10K, GMM2642233BL TG-10K 7042S
Samsung	KMM366S104BTN, KMM366S403BT2

Table 2: Vendors of compatible SDRAM DIMMs

Fujitsu

Hyundai

IBM

Micron

Optosys

SEC

Table 3: Vendors of in- compatible SDRAM DIMMs

Acer

Asus

Samsung

Table 4: Parts that work in my own G3

Vendor Name	DIMM part number	RAM part number	Capacity
LG Semicon	GMM	LG Semicon LGS	32MB
(preinstalled)	2644133BLTG-10K	GM72V16821BT10K
Hyundai		HY57V651620TC-10	64MB

The Technical Information [6] that ships with the computer provides the following information concerning the DIMM-specifications:

The main logic board has three expansion slots that accept 1.15-inch DIMMs that meet these specifications:

• 8, 16, 32, or 64 MB
• 3.3 volts (V), unbuffered, 64-bit wide, 168-pin
• 100 MHz/10 nanoseconds (ns) cycle time or faster using SDRAM

As you can see in figure 1, there is a restriction in the height of the DIMMs. They may only be as high as 1.15 '', which is approximately 29 mm. Higher modules won't fit in the G3-Desktop cases. Note that [6] also mentions that the maximum amount of DRAM that can be installed is 192MB, which supercedes other decumentation that says you can install a maximum of 384MB. Where the 192MB configuration is acheived by filling all three slots with 64MB DIMMs.

Figure 1: Dual Inline Memory Module (DIMM)