dave@arnold.UUCP (Dave Arnold) (06/20/87)
I found a disk drive I am interested in for upgrading my 7300. It is the Miniscribe 3053. It's a half height drive with a rotary voice coil. It has 44.6 formatted capacity, has an access time of 25ms, and is supposedly vvverrryy quiet :-) . It has a list price of $625 (I think), and I believe I can get it cheaper. However, it has a ST412 interface. Not ST506 or ST506/412, but ST412 only. I talked to an somebody at Miniscribe, and @ first said it would be no problem interfacing. Then he paused, and said he wanted to talk to an engineer, and would call me back. After calling me back, he then wanted to know how old the machine is (he didn't know what a UNIXpc was!). Supposedly, ST506 came before ST412 and old controllers don't support ST412. ST506 doesn't do buffered seeks, ST412 does. My questions are this: Can the disk drive controller on the UNIXpc motherboard do ST412 buffered seeks? Is the differences between ST506 and ST412, which I stated, correct? What exactly is a buffered seek? In general, anybody know for sure if this drive will work as it should on the UNIXpc? Dave Arnold UUCP: ...seismo!uunet!arnold!dave attmail!arnold!dave
karl@ddsw1.UUCP (06/24/87)
In article <117@arnold.UUCP>, dave@arnold.UUCP (Dave Arnold) writes: > > What exactly is a buffered seek? > A buffered seek is a seek command without a specified time-per-cylinder step. The drive is supposed to coordinate the request, and let the controller know when the operation is complete. This is in contrast to a timed seek, where the controller issues step pulses at a fixed rate. The advantage of this is that on a long traversal of the media, you can often speed up in the middle, getting *much* better performance (since the head is already moving, inertia can be disregarded on the middle seek pulses, and thus, the seek is completed faster). Most current drives can perform this task -- and drives which can do buffered seeks can usually handle 'regular' seeks as well.
davidsen@steinmetz.steinmetz.UUCP (William E. Davidsen Jr) (06/25/87)
ST506 does unbuffered seeks. The communication between the controller
and the disk is in the form:
step..done..step..done..step..done
for ST412, the buffered step looks like:
step..step..step..step..done
The step commands from the controller are saved (buffered) in the disk
electronics, and the drive sends back a done when all step commands are
satisfied.
Some disks take better advantage of buffering than others; a drive may
be conforming and just use a counter, or it may do neat stuff like
accelerate the heads half way to the final destination and brake them
for the remaining half. This is called a "balistic seek" (sp?) and makes
long seeks almost as fast as short seeks.
--
bill davidsen (wedu@ge-crd.arpa)
{chinet | philabs | sesimo}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me