tezza wrote:One the point of discussion though, did something like PRODOS (for the Apple IIe range) support double density? Or does this term have no meaning with Apple II Disk technology, given it's stripped-down chipset is quite different from other disk controller read/write conventions of the time? Just curious?
It's not that the term has no meaning... Just that for a long time, realistically only one basic density was supported by the chipset. (There were others, but they tended to be a bit hamstrung by being only useful to a ProDOS user. 99% of game loaders were expecting a DOS 3.3 derivative and that really was only written for the Disk II, so things stayed static for a long while until some software started needing ProDOS)
I think the Apple II's ubiquity was the source of this, also... Unlike the C64, cassette use on the Apple II stopped almost immediately and the Apple II spread quickly in a
very standard disk-based format and attempts to change it would fail because they had no real driving impetus. Look at how minimal the uptake of "superfloppy" type disks were in the PC world, right to the end of the floppy. The ubiquity of BIOS support for 1.44MB (and horribly patchy support for most other things) ensured NOTHING ever really replaced the 1.44MB until it became too small for anything current. Hell, the 1.44MB survived the patchy transition to CD/DVD boot and outlived BLU-RAY. (Seen a BLU-RAY drive in a laptop lately? It's either no-optical drive or DVD "if they must")
Floppy really has only finally died in servers as support for USB boot is reasonably reliable.
I could speculate that the
early CP/M world had enough different vendors that diversity of density was possible and ended up widely supported, and to some degree, progress was desired and
expected... however I digress.
The Disk II supports 40 tracks, single sided, and the DOS normally used 35 of these at 16 x 256bytes per track. I think there was the odd modified DOS that used the full 40, but nothing official. Tended to be restricted to game loaders wanting to squeeze a bit more onto the disk.
It also happened a bit less because where other machines were using MFM encoding, the Apple II's GCR was a bit more efficient. i.e. 140k where MFM would achieve <100k. So for a while, if software was being ported from another platform, the 140k was adequate. It also made it a bit faster (and cheaper) than most drives with the 16 sector GCR implemented pretty much all in the controller. The downside is this fairly optimised chipset knew nothing about MFM until well after the IIgs, so there's absolutely NO CHANCE of ever reading a (native) CPM or DOS disk in a Disk II with the standard controller. (
maybe, one of the later "superdisk" controllers, but ... gold plated hens teeth)