Information for Tseng Chipset Users : linear memory base address (MemBase) issues : Restrictions
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## 9.5. Restrictions

There are some limits as to where the linear memory base may be put. On any ET4000W32, it must have a 4MB granularity (i.e. it can be put at 16M or at 20M, but not at 18M). On ET6000, it needs a 16M granularity (note: the ET6000 driver should be able to determine the linear memory base automatically, so you should never need to define MemBase in the first place).

On ET4000W32i, things are worse: the linear address base is hardwired on the card, and there is no reliable way to read it back from the card. You need to know the address in some way, and specify it. The current code does an intelligent guess at it, but this is no guarantee.

On ISA cards, things are much more simple: ISA only uses 24 address lines, and hence the linear memory MUST lie within the 16 MB boundary. Together with the 4MB granularity of the linear memory base address on ET4000 cards, this means that you cannot have more than 12 MB of system memory in the machine if you want to use linear memory. Hence, the only realistic MemBase for ISA cards is 0x00C00000. This is also what the server will automatically choose if it detects an ISA W32 card.

WARNING: you must not have over 12 MB of system memory in this case. Or if you have it, you must disable access to all memory above the 12 MB mark. Some operating systems allow you to specify at startup how much memory it is allowed to use, so you don't have to unplug some memory each time you want to use linear memory.

Information for Tseng Chipset Users : linear memory base address (MemBase) issues : Restrictions
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