The following changes have been implemented in the BART21 controller chip:
- BART4 would not allow NuBus Master cards to perform burst reads of main memory (burst writes were fine) unless the bus frequency was a multiple of 40MHz. BART21 corrects this problem.
- BART4 would only enable bursting to a slot when the burst enables for all slots were set. BART21 provides burst enable on a slot-by-slot basis.
- BART4 only provided access to slots 9-E (and software couldn't take advantage of slot 9 support). BART21 adds standard slot spaces for slots 1-8, and superslot space for slot 8.