Path: utzoo!mnetor!uunet!husc6!rutgers!rochester!cornell!uw-beaver!tektronix!dadla!amadeus!jamesa
From: jamesa@amadeus.TEK.COM (James Akiyama)
Newsgroups: comp.sys.ibm.pc
Subject: Re: No problem AT clones (Flame on Compaq)
Message-ID: <866@amadeus.TEK.COM>
Date: 12 Dec 87 01:55:37 GMT
References: <2001@briar.Philips.Com> <3151@bnrmtv.UUCP> <636@qetzal.UUCP>
Organization: Tektronix Inc., Beaverton, Or.
Lines: 62
Keywords: clones ruinous hardware tweaks doom frustration exasperation
Summary: Portable Compaq Fixed Disks


Mr. White Writes:

> Unfortunately, the Compaq had a CDC type 17 drive in it and nonstandard
> connectors (the pin type as opposed to the edge connectors). 
> If this is Compaq's cute idea of locking you into their hard drives,
> it didn't seem very funny as I drove 170 miles on icy
> roads in the middle of a snowstorm in the middle of the night
> to meet the rest of the Compaq in Burlington, Colorado to pick up
> the machine and meet a 9 a.m. deadline back in Denver the same morning.

There are other possible explanations for Compaq choosing this "nonstandard"
connector scheme.  I believe you will find that this connector is really a
modified (and stripped-down) IBM PC/AT style interface.  This interface is
actually very close to the interface used on many of the "hard-card" drives.
The "standard" interface today is the ST506/412 interface using MFM encoding.
This "standard" is beginning to become outdated.  Major limitations include:

    1.	Approximately 160 MEG capacity limit due to head, cylinder, and
	and track density limitation imposed by standard.

    2.	Maximum transfer rate of 5 megabits/second (1/2 megabyte/second)
	transfer rate.

By having the interface AT-style and placing the fixed disk controller on the
fixed disk itself, these limitations can be overcome in future disk drives.
Compaq has already done this with their 100 MEG drive option in the Portable
386.  This 3 1/2" drive (made by Connors Peripheral) uses an embedded SCSI
controller using 2,7 RLL encoding.  This allows an effective transfer rate
five times faster than the "standard" AT-style controller (since AT's normally
require an interleave of 2:1).  It also allows better optimization of the
controller to the fixed disk often times yielding a better average seek time
and overall performance.

Note that this drive may be plugged into any Compaq which supports the drive
type number WITHOUT CHANGING THE CONTROLLER BOARD.  This drive would require
a new controller card in most AT-clones, which is nearly impossible in Compaq's
portables since they include other functions on the controller board (I assume
for size reduction reasons).

Other advantages could be stated including manufacturing cost reduction on
computers configured without fixed disks (including a "diskless" node to a
network) since such a unit does not have a useless fixed disk controller
included.

As for adding a "non-Compaq" fixed disk; you might try contacting a local
Western Digital dealer.  I believe that they actually do manufacture the
embedded controller for ST506 MFM drives used on Compaqs.  I believe the
controller is their WD1003-IDX controller and is again similar to the
controller they use on their hard cards.  I am not sure whether Western
Digital sells these outright or just to OEMs but it's probably worth a try.

I realize that this may be make third party upgrades inconvenient and difficult
but as a design engineer myself I know that often times tradeoffs must be made
between overall performance and ease of option installations.

Note that I am not affiliated in any way to Compaq computers (I work at
Tektronix, Inc.) other than owning a Compaq computer myself.  This information
is my own options and does not necessarily reflect the view of Tektronix, Inc.
I hope this information is helpful.

					James Akiyama