This program displays memory size, bank configuration, and interleave status for each DIMM slot. This program can be used to detect if DIMMs have been installed properly to enable interleaving.
This program only runs on Hammerhead-based PCI PowerMacs, such as the 7300, 7500, 7600, 8500, 8600, 9500, and 9600 computers. It doesn't support any Nubus machine, including the original PowerMac, or PowerMacs which use a memory controller other than a Hammerhead-based, such as the 4400, 6400 or 7200.
The program returns one of three possible results. On Macs which don't support the Name Registry, such as Non-PCI Mac, it will generate a Finder error message, such as -192 or "NameRegistryLib" could not be found. On unsupported PCI Macs, such as 6400s, the application will report that it is not supported. Otherwise, on the supported PowerMacs, it will generate a list that looks like this:
A1/B1 (row 0) -> w/x interleaved
A1/B1 (row 1) -> y/z interleaved
...
An/Bn (row 0) -> r/s interleaved
An/Bn (row 1) -> t/u........----
An/Bn represents a pair of slots. On the 8 slot Macs (7500, 8500, etc.) there are four pairs A1/B1 thru A4/B4. On the 9500/9600, there are six pairs of slots (A1/B1 thru A6/B6).
A DIMM can have either one or two rows of memory. Interleaving is performed by matching the rows of corresponding DIMM slots. Hence, A1 row 0 is paired with B1 row 0, and A1 row 1 is paired with B1 row 1. (The rows of a DIMM module do not correlate to the physical attributes, such as the side of a board. For example, single row could encompass both sides of a DIMM, while a dual row could fit onto a single side.)
w, x, y, z represent the size of a memory row. To determine the total size of DIMM A1, add w+y. For DIMM B1, add x+z.
If a row is interleaved then "interleaved" will appear at the end of the line.
Background: What is memory interleaving and what advantage does it provide?
Even though the system data bus is 64 bits wide, a PowerMac with a Hammerhead-based memory controller such as the 7300, 7500, 7600, 8500, 8600, 9500, and 9600 computers can support 128 bit data read and write operations to main memory by accessing data from corresponding DIMMs simultaneously.
Memory interleaving provides higher bandwidth (MBytes per second) between the PowerPC microprocessor and main memory, which can provide a significant performance boost by increasing the execution speed of memory-intensive programs. How much faster depends on a program's software architecture and how often the processor accesses cache (L1 & L2) versus main memory.
Detecting Interleaved memory...
Memory interleaving is a function of the memory controller and is automatically enabled by the power-up software when it detects two DIMMs in corresponding expansion slots (such as, A1 and B1, A2 and B2, and so on) that are the same size, have the same memory bank configuration, and have the same DRAM addressing modes.
It is non-trivial to look at two DIMM modules and determine if interleaving will be enabled (assuming they are placed in corresponding slots). Even if two DIMMs are the same size (i.e. 16 meg.) and have the same number of chips (i.e. 8), they may be configured differently such that interleaving is not enabled. The only safe visual method is that all of the DRAM on both DIMMs have exactly the same part number.
Source code to this program is provided as sample code for developers. The intent is that developers will provide this functionality into a program to assist customers in purchasing and configuring DIMM modules for optimal system performance. It should be possible to build an "expert system" which explains to customers how to configure their memory for interleaving (place DIMM from Slot A1 into Slot A4, etc.)
