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From: neff@hpvcfs1.HP.COM (Dave Neff)
Newsgroups: comp.sys.mac
Subject: Re: HP DeskWriter Performance on a Plus
Message-ID: <780065@hpvcfs1.HP.COM>
Date: 2 Oct 89 18:01:54 GMT
References: <22051@cup.portal.com>
Organization: Hewlett Packard, Vancouver, WA
Lines: 49

In article <780063@hpvcfs1.HP.COM> neff@hpvcfs1.HP.COM (Dave Neff) writes:
>Prior to the DeskWriter there was no "HP blessed" solution to using
>DeskJets with the Mac.  The DeskWriter is specifically designed and
>optimized for use with the Mac.
>
>Of course third party alternatives (chooser drivers with various
>high speed serial or SCSI to centronics converter) are always possible,
>
>Certainly some sort of hardware converter could put
>performance closer to the DeskWriter (the DeskWriter would still be a
>bit faster due to bi-directional graphics and other enhancements).

>>Now I'm totally confused.  Are you saying that if
>>HP were to offer a DeskWriter option that used a
>>SCSI connection to the printer, it would not yield
>>improved speed over the present DeskWriter configuration?

No you aren't confused.  Adding a faster interface to the DeskWriter
would not improve performance.  Why?  The DeskWriter can only
mechanically pick up paper and move the print head over the paper
at about a 1 page per minute rate.  This is the rate the DeskWriter
runs on a Mac II for most cases.  The DeskWriter is not IO limittted,
it is mechanism limitted, so faster IO would make no difference.

>>BTW, what is the DeskJet interface?
>>LocalTalk?  Serial at some high baudrate?
>>Is the DeskJet driver an in-house development,
>>or did HP acquire it from Insight or somewhere
>>else outside?

The DeskWriter has a 57K baud serial interface.  The DeskJet/DeskJet+ has a
19.2K baud serial and a parallel interface.  On the DeskJet+ the
parallel interface can run much faster than 19.2K baud.  That is, the
DeskJet+ will be IO limitted at 19.2K baud but will be mechanism
limitted using the parallel port (assuming the application/driver can
generate graphics at a 1 page per minute rate or better). 
Hence a hardware converter for the Mac could boost performance for a
DeskJet+ (IO limitted) but would make no difference for a DeskWriter
(mechanism or CPU limitted).  The DeskWriter also has mode 3 graphics
which results in much greater graphics compression than the mode 2
support in the DeskJet+.  This also helps the DeskWriter to not be IO
limitted at 57K baud.

The DeskWriter driver was written in house with help from Palomar
Software and using the Compugraphics Intellifont outlines and filling/
scaling algorithms.

Dave Neff
neff@hpvcfs1.HP.COM