SDRAM Bank Interleave

Common Options : 2-Bank, 4-Bank, Disabled

Quick Review

This BIOS feature enables you to set the interleave mode of the SDRAM interface.

Interleaving allows banks of SDRAM to alternate their refresh and access cycles. One bank will undergo its refresh cycle while another is being accessed. This improves memory performance by masking the refresh cycles of each memory bank. A close examination will reveal that since the refresh cycles of all the memory banks are staggered, this produces a kind of pipelining effect.

However, bank interleaving only works if the addresses requested consecutively are not in the same bank. If they are in the same memory bank, then the data transactions behave as if the banks were not interleaved. The processor will have to wait until the first data transaction clears and that memory bank refreshes before it can send another address to that bank.

Each SDRAM module is internally divided into either two or four banks of memory. Double-banked SDRAM modules generally use 16 Mbit SDRAM chips and are usually 32 MB or smaller in size. Quad-banked SDRAM modules, on the other hand, usually use higher density (64-256 Mbits) SDRAM chips. All SDRAM modules of at least 64 MB in size are quad-banked in nature.

If you are using a single double-banked SDRAM module, set this feature to 2-Bank. This is the only option available for the single double-banked SDRAM module.

If you are using at least two double-banked SDRAM modules, you can use the 4-Bank option as well as the 2-Bank option. Of course, it is recommended that you select 4-Bank for better interleaving performance.

If you are using quad-banked SDRAM modules, you can use either interleave options. Of course, it is recommended that you select 4-Bank for better interleaving performance.

Because a 4-bank interleave always allows for better interleaving performance, it is highly recommended that you select the 4-Bank option if your system supports it. Use the 2-Bank option only if you are using a single double-banked SDRAM module.

Please note that Award (now part of Phoenix Technologies) recommends that SDRAM bank interleaving be disabled if 16 Mbit SDRAM modules are used. This is because early 16 Mbit SDRAM modules have stability problems with bank interleaving. The good news is all current SDRAM modules support bank interleaving.

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