There are SIMMs (Single Inline Memory Modules)
and DIMMs (Dual Inline Memory Modules - count the pins on both sides of the module)
These two are long and rectangular, like a stick of chewing gum
Next there are SODIMMs (Small-Outline Dual Inline Memory Module) which are shorter and more square - relatively shorter along the contact edge. These are mostly laptop RAM.
A RAMBus RIMM (RAMBus Inline Memory Module) is a type of DIMM, but is electrically in a world of its own. Fast, for its time, but too expensive and was ousted from the market by cheaper DDR DIMMs.
Then, classify the module by the number and placement of pins:
30 pin SIMM - big, fat contacts, early compact Macs and Mac IIs up to the Quadra 700 - some models required banks of 4
64 pin SIMM, special for Mac IIfx and LaserWriter IIntx, very rare
72 pin SIMM - Mac LC. Performa, Quadra, often had to be installed in pairs, up to PowerMac 6100s Could be FPM or EDO, difficult to tell
72 pin SODIMM - used in some IBM and Toshiba Laptops, never used in Macs
100 pin DIMM *also called SODIMM* - printer RAM for HP laser Printers and the like
EDO 144 pin SODIMM - used in some IBM and Toshiba Laptops, never used in Macs
144 pin SDRAM SODIMM -- 72 per side, "laptop" RAM, could be PC66. PC100, PC133 (should be labelled): iMac G3 Tray load 233-333 MHz, most Powerbook G3, iBooks up to G3, Titanium Powerbook G4, iMac G4 700 and 800
168 pin 5V DIMM - PowerMacs 7200 through 9600 Can be either EDO or FPM, difficult to tell unless labelled. EDO must not be used in the PM 7200. 5.25" long
168 pin 3.3V EDO DIMM - PowerMac 4400 and Motorola Starmax Mac Clones. 5.25" long
168 pin SDRAM DIMMs - PC66, PC100, PC133 Synchronous RAM - should be clearly labelled with the speed - 1Mac G3 250 MHz and above, G3 & some G4 machines, some USB 1.1 eMacs 700 MHz - 1 GHz 5.25" long
184 pin DIMM - DDR DIMM, PC2700, PC3200 Mirror Disk Drive G4's, Single and Dual Processor PowerMac G5's, Mini G4, iMac G5 Rev A and B, USB 2.0 eMacs 1 GHz and up 5.25" long
200 pin SODIMM DDR for Aluminum G4 Powerbooks (15 and 17" up to Oct 19 2005, and all 12" to date), iMac G4 1 GHz and up
240 pin DDR2 DIMM 533 MHz - Dual-core PowerMac G5, iMac G5 iSight model
200 pin DDR-2 SODIMMs - intel Macs 667 MHz, the Powerbook G4 HD (DL) model used 533 MHz.
RAMBus 184 pin RDRAM RIMMs - never used in Macs.
I have glossed over a few types here, there are several types of VRAM used in Macs, plus some proprietary modules used in early Powerbooks, and several different types of MicroDIMM used in PCs. There is also a 232 pin 32-bit RAMBus which is exceedingly rare.
If the module has a multiple of 4 (8, 16, 32) memory chips on it, it will be a standard, non-ECC module. If it has a multiple of 3 (9, 18, 26) then it is an Error correcting (ECC or parity) module used in servers, and almost never in Macs.
Capacity is harder to determine, if the label has no information.
We have more definitions at
http://www.canadaram.com/glossaryofterms.htm
Thanks
Trevor
CanadaRAM.com
