The accelerated 256-color driver uses 256 bytes of scratch space in video memory, and the hardware cursor also uses 1K. Consequently, a 1024x1024 virtual resolution should not be used with a 1Mbyte card.
The use of a higher dot clock frequencies has a negative effect on the performance of graphics operations, especially BitBlt, when little DRAM bandwidth is left for drawing (the amount is displayed during start-up). With default MCLK setting (0x1c) and a 32-bit memory interface, performance with a 65 MHz dot clock can be half of that with a dot clock of 25 MHz. So if you are short on DRAM bandwidth and experience blitting slowness, try using the lowest dot clock that is acceptable; for example, on a 14" or 15" screen 800x600 with high refresh (50 MHz dot clock) is not so bad, with a large virtual screen.
It does not make much sense performance-wise to use the highest clock (85 MHz) for 1024x768 at 76 Hz on a 542x; the card will almost come to a standstill. A 75 MHz dot clock results in 70 Hz which should be acceptable. If you have a monitor that supports 1024x768 at 76 Hz with a 85 MHz dot clock, a standard 5426/5428 based card is a poor match anyway.
5434-based cards with 2Mbyte of memory do much better at high dot clocks; the DRAM bandwidth is basically double that of the 542x series. The 543x chips also make more efficient use of the available DRAM bandwidth.
Next Chapter, Previous Chapter
Table of contents of this chapter, General table of contents
Top of the document, Beginning of this Chapter