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SIMMs (Single Inline Memory Modules) come in powers of 2, i.e., 1,2,4,8,16,32, etc. They are about 1 inch by 5 inches in size, and snap into simm sockets on the system board (also called motherboard, mainboard, or systemboard) SIMMSs are used only on legacy systems, generally anything thats older than 4 years will use SIMMS.

Parity vs. Non-parity: Most MacIntoshes use nonparity simms (x8, x32), and most PCs use parity simms (x9, x36). However,  the recent trend is using non-parity simms on Pentium systems because parity is not required on most 64-bit systems.  Another type of memory is ECC (error code correction) used on high-end servers. These modules are self-diagnosing and fix any errors. Parity is IHMO a waste of money, time and effort. because if a Simm detected a single bit parity error, it would halt the machine.

A 30-pin simm is parity if it has chips in multiples of 3 (or 9). If it has chips in powers of 2 (2, 4, 8, ...)  then it's non-parity. 72-pin SIMMs are more difficult to identify visually due to the many different possible chip  configurations on SIMMs made by different manufacturers.

A high-density SIMM is one which has been designed with higher-density memory chips (each chip is 64Mbit instead  of  16 Mbit), resulting in a reduced chip count. Many of the new machines that use 64MB SIMMs (16x32, 16x32EDO, 16x36) may require SIMMs with high density chips. Low density is a standard 32 or 36 chip configuration;  high density will be  an 8 to 12 chip design, which tends to have a slightly higher cost.

Common 30 pin simms are 1MB-1x8, 4MB-4x8 (nonparity) and 1MB-1x3, 1MB-1x9,  4MB-4x9 (parity); common types of 72-pin simms are 4MB-1x32, 8MB-2x32, 16MB-4x32 (nonparity) and 4MB-1x36, 8MB-2x36, 16MB-4x36 (parity). The "1x32",  part is the simm specification, also referred to as  'architecture', because it indicates the simm design in terms  of number of chips on the simm, and density of those chips. If you multiply the 2 numbers out, you get the total number of megabits and then divide by 8  (for nonparity simms) or 9 (for parity simms) to get the size in megabytes. 72-pin  SIMMs will also differ visually from a 30-pin SIMM by having a notch in the middle of the connector.

All I can say about logic parity or logic generated parity is "NO", stay away from it. Someone came up with the idea of tricking the memory manager into believing the SIMM is  parity. Not Good! Stay away!!!