Looking for a ST419

It's not conceptually that complicated. The basic idea is to have an 'image' of a track stored in some kind of semiconductor memory. And you keep on replaying that a s bitstream into the read data input of the controller, generating an index pulse of course at the appropraite time. When you get a write gate fro mthe controller you then start sampling the write data output from the controller and overwriting the stored bitstream. Yes, there might be glitches at the start/end of a write, but presumaly no wores than on a physical disk. On a head swtich or head step (to a different cylinder) you replace the image in memory with the correct one for the new track. The problem is in the details. In particlur I don't think any normal flash memory will be fast enough to directly read out the track image and blast it to the controller, and I'm darn sure it's not fast enough for a direct write. Which means you need to have a buffer memory of high-speed SRAM to store the current track image This needs to be loaded from flash on a track change, and written back afterwards _iff it was updated by the controller_ Now, there are 2 types of track change, a head switch and a cylinder movement .The latter is easier, since it can take as long as you like (within reason), there's a seek-complete line back to the controller. But a head swithc has to be essentially instantaneous. Which probably means having enough SRAM to buffer the tracks for all heads on a given cylinder and then keeping an 'undated' flag for each track, writing back only those that have changeed. I didn't think SPI was anything like fast enough for this. I looked into using a _lot_ of F-series TTL chips, and rather gave up on the idea. Maybe I should have another go. -tony