• Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint
Share this Page URL

Chapter 4. Memory > Pre-PowerPC G3 Mac Memory Tips

Pre-PowerPC G3 Mac Memory Tips

Here are a few performance and upgrading tips for pre-G3 series Mac owners.

Memory Interleaving

Many Power Macs (7300 to 9600) and Mac OS clones (Power Computing PowerTower Pro and PowerWave, Umax SuperMac S900 and J700) can use interleaved RAM. Even though the system data bus is 64 bits wide in these models, the memory controller can handle 128-bit data read/write operations by interleaving data between corresponding DIMMS. Interleaving memory provides higher effective transfer rates (called bandwidth) between the CPU and main memory. The benefits vary by application, and the highest gains are seen with programs or games that move a lot of data over the bus. For a performance comparison of interleaved RAM, see www.xlr8yourmac.com/RAM/. Power Mac G3 series and later Macs use SDRAM and don't support memory interleaving by DIMM pairs. (SDRAM interleaves RAM on each DIMM and has much higher bandwidth due to higher clock speeds.)

For Macs that can use it, you interleave RAM by installing identical (size and type) DIMMs in matching A/B slots (for example, A1/B1, A2/B2, and so on). So, if you install a 32 MB DIMM in slot A1 and a matching 32 MB DIMM in slot B1, the Mac will interleave access to those DIMMs.

RAM Tips for CPU Upgrades

If you're considering a CPU upgrade, be aware that some upgrade cards may not be stable with interleaved RAM. I've not had this problem when using matched DIMMs (same manufacturer, 60-nanosecond speed rating) with any CPU upgrade I've tested personally. However, some visitors to my Web site have had this problem, due to the almost infinite variety of older RAM types and speeds found in many Macs. The design of the CPU-upgrade card can also affect stability. For thousands of owner reports on CPU upgrades in older Macs, search the database at http://forums.xlr8yourmac.com/cpureview.lasso.

Owners of Macs with six PCI slots considering a Newer Technology CPU upgrade should note that Umax was the first to report an issue with certain types of buffered RAM. Full details on the issue and how to check the memory you have were originally in the Umax knowledge base but have been removed. See the CPU Upgrades or Memory Questions section of the AccelerateYourMac FAQ (http://forums.xlr8yourmac.com/faq.lasso) for details.

2K Refresh and 4K Refresh Memory

Main memory has to be refreshed to maintain the memory contents. You'll often hear 2K refresh or 4K refresh in discussions about older Mac RAM. This refers to the number of refresh cycles required for all sections of the memory array. It is determined by the number of row addresses on the module. For example, a 4-Mb by 4-bit wide memory chip can be configured as either 2K or 4K refresh. Memory with 4K refresh has 12 row addresses and 10 column addresses, and 2K refresh has 11 row addresses and 11 column addresses. For more information on refresh rates, see the Power Macintosh: Memory FAQ at http://til.info.apple.com/techinfo.nsf/artnum/n20575.

  • Creative Edge
  • Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint