11 Feb
2021
11 Feb
'21
10:57 a.m.
On Feb 11, 2021, at 1:46 PM, Chuck Guzis via cctalk
<cctalk at classiccmp.org> wrote:
On 2/11/21 10:22 AM, Jon Elson wrote:
Then again, ST412 with its buffered seek is vaguely like having a real SEEK command,
it's just less elegant because the cylinder number is encoded in base 1.
paul
No. ESDI is similar to MFM, there is a
differential read data pair on
the 20-pin connector, but the data rate is much higher, 10, 15 or 20
MBit/sec, and used a different encoding scheme that gave more data
bits/flux transition. I think the 34-pin connector also allowed an
additional head select bit,
so you could have up to 16 heads.
ATA has a single 40-pin connector with a 16-bit parallel data bus for
all command and data transfers.
Brevis esse laboro, obscurus fio.
Let me be more concise. On an x86 PC, *most* ESDI controllers present
an interface exactly like ATA, right down to the IDENTIFY command.
If you're talking about the naked drive, it isn't ATA, nor is it similar
to MFM. ESDI drives are "smart" in the sense that they do have a
command set (not ATA, however) and perform tasks such as data separation
and seeking (one issues a SEEK command to the drive, not a STEP IN/OUT).
ST506, in contrast, is a glorified floppy drive with differential data
interface--it has no smarts. ...