Firmware 0.7A-F14 improves write performance for HD20 emulation. With the old firmware, if you wrote a 1 MB file to the disk, it would do 2000 separate 512 byte writes to the SD card. SD cards really don’t like this! With the new firmware, the Emu hardware uses an internal 10K RAM buffer, and does 100 separate 10K writes to the SD card. Read behavior is unchanged, so read performance will be the same as before.
Combo Firmware 0.7A-F14
The performance gain vs the old firmware for HD20 writes depends on the model of Macintosh, and the size and type of SD card used. Faster Macs like the IIci will see more benefit than a Mac Plus, since I/O in the faster Macs is less constrained by CPU speed and more directly tied to the actual disk throughput. SD cards with a larger erase page size will also see more benefit from this new firmware. The erase page size is the native block size of the SD card, and typically is something like 4K. When performing a small 512 byte write, the SD card must read an entire 4K block from flash memory into an internal RAM buffer, erase the whole block of flash, update the 512 bytes of the buffer that are being modified, then write the whole 4K buffer back to flash memory. The larger the erase page size, the more inefficient this process is for small writes, and the more this new firmware will help. Unfortunately erase page sizes aren’t normally advertised, but larger SD cards usually have a larger erase page size than smaller cards. For this reason, the best Emu performance in both HD20 and floppy modes will typically be achieved with a small capacity SD card. Use a card of 2 GB or smaller if you can find one.
On a Mac IIsi with an 8 GB SD card, this new firmware provided a 40% improvement in HD20 write speeds in my testing. With a 2 GB card, the improvement was 8%, but it was still faster in absolute terms than the 8 GB card. Interestingly, the 2 GB card with old firmware had the same performance as the 8 GB card with new firmware, so erase page size really matters! On a Mac Plus with the 8 GB card, the new firmware resulted in about a 36% improvement in HD20 write speeds. With the 2 GB card there was no measurable write speed improvement on the Mac Plus. Bottom line: use a small capacity card in combination with this new firmware for the best HD20 write speeds.