spacewar at gmail.com
Tue Jul 17 18:11:48 CDT 2018
On Tue, Jul 17, 2018 at 2:49 PM, Grant Taylor via cctalk <
cctalk at classiccmp.org> wrote:
> I conceptually get that the GoTEK can't go any faster than the Floppy's
> IDE (I thought floppy was a derivative of IDE.) bus can carry the data.
IDE came much later and isn't very similar to the floppy interface. Here's
more history of it than you probably wanted:
IBM invented the 8-inch floppy drive and had a proprietary interface to it
(discussed here recently). Memorex made plug-compatible drives, but the IBM
interface did not become an industry standard. With IBM's earliest floppy
drives (23FD "Minnow"), even the medium, rotation rate, data encoding, and
index hole locations weren't compatible with what became the industry
standard. Minnow was shipped to customers as part of IBM mainframes and
control units as a read-only device to load microcode, though obviously
internally IBM had equipment to write the disks. IBM redesigned it as the
33FD "Igar", and that did set an industry standard for the media format,
but still did not standardize the electrical interface.
The Shugart SA-900/901 drive standardized a 50-pin interface for eight-inch
floppy drives. The Shugart SA-4000 series 14-inch winchester hard disk
drives used a similar but not identical 50-pin interface. The SA-1000
series 8-inch winchester hard drives moved the data to a "radial" interface
using separate connectors for each drive, while keeping the 50-pin
interface for control and status. The SA-4000 and SA-1000 series
established defacto standards for early winchester drives.
Shugart invented the 5.25-inch floppy drive. The Shugart SA-400 drive
standardized a 34-pin interface for 5.25-inch floppy drives, which was for
the most part a subset of the 50-pin interface, with the pins rearranged.
Most 5.25-inch floppy drives provided spindle motor on/off control over the
interface but had no head load solenoid, where previously most 8-inch
floppy drives gave the interface control over the head load solenoid but
had no spindle motor control. (Many of the later 8-inch half-height floppy
drives followed this trend.)
The Shugart Technology (a different company, later renamed Seagate) ST-506
drive standardized a 34-pin interface for 5.25-inch winchester hard drives,
which was in most regards a subset of the SA-1000 interface, with a
different pinout, and a different differential signalling standard (RS-422)
on the radial data connector.
When 3.5-inch floppy drives and hard drives were introduced, most used the
same 34-pin interfaces as their 5.25-inch counterparts.
All of the drives and interfaces previously described are bit serial, with
discrete control lines for all drive functions. The interfaces have no
parallel bus structures for either data or control.
There were third-party hard disk systems for the IBM PC, but the first
official IBM hard disks for PCs were for the PC/XT and PC/AT. The PC/AT
controller in particular was based on a Western Digital design.The IDE hard
disk interface was essentially the host interface of the Western Digital
hard disk controller. As such, it uses a parallel data bus for both data
and commands. There are no discrete drive control signals.
> I was hoping to avoid some timings of the physical aspects of spinning the
> disk and seeking.
Unfortunately not. A floppy drive doesn't have any way to know what sector
the host wants, so a drive emulator has to simulate the rotation process.
Most floppy interfaces, including those used on PCs, don't have buffered
seek, so there's no easy way for the emulator to short-circuit the step
process either, though you could possibly tell the computer to configure
the floppy disk controller chip for a faster seek rate.
More information about the cctech