XTIDE controller now available
ggs at shiresoft.com
Mon Oct 5 20:57:33 CDT 2009
On Oct 5, 2009, at 2:10 PM, Dave McGuire wrote:
> On Oct 5, 2009, at 3:39 PM, Geoffrey Reed wrote:
>>> What am I not understanding about the need for this product? I
>>> have about
>>> a half-dozen 8-bit ISA IDE controllers, mostly Seagate branded.
>>> think they were particularly rare.
>> From what this sounds like it is able to talk to large capacity IDE
>> presumedly 16-bit IDE drives. The older XT ide controllers by
>> seagate (that
>> I had) were limited to a handful of drives that could do 8-bit wide
>> transfers and were very limited capacity wise.
> The big difference here is LBA vs. C/H/S addressing. Recall that
> the IDE interface is a clone of the register-level programming
> interface of the ancient WD1010 MFM hard disk controller chip
> family, whose registers are 8 bits wide. There's a register for the
> starting sector number (256 sectors), a register for the low byte of
> the cylinder address and two bits of another register for the high
> part of the cylinder address (meaning it tops out at 1024
> cylinders), and half of a register for the head number (meaning 16
> 1024 cylinders * 16 heads * 256 sectors * 512 bytes/sector = 2GB
> I don't know where any supposed 520MB limit comes from; if someone
> can enlighten me there, I'd appreciate it.
It was originally 63 sectors. I was one of the 3 people at IBM who
came up with this scheme (because the controller we had did LBA
addressing so we needed a way to map C/H/S to LBA in a simple way).
We *knew* at the time that this was constraining but we figured that
LBA would be in place before we hit the limit. We were wrong.
TTFN - Guy
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