One chip that could be used as a memory mapper for the 9900 (but wasn't in the TI99/4A) was the 74LS670, which was used in the IBM 5150 PC to allow the 8237 DMA chip to access more than 64KB (a limit that wasn't a problem when used in a 8080 system).
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One chip that could be used as a memory mapper for the 9900 (but wasn't in the TI99/4A) was the 74LS670, which was used in the IBM 5150 PC to allow the 8237 DMA chip to access more than 64KB (a limit that wasn't a problem when used in a 8080 system).