Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!nstn.ns.ca!wrdis01!mips!rat!vlsisj!seiler
From: seiler@vlsisj.uucp (%)
Newsgroups: comp.sys.mac.misc
Subject: Re: Mac Vs. Windows? (sorry)
Message-ID: <1991May29.200007.9448@vlsisj.uucp>
Date: 29 May 91 20:00:07 GMT
References: <674648116.0@blkcat.FidoNet> <4799@gmdzi.gmd.de>
Sender: usenet@vlsisj.uucp (Usenet News)
Reply-To: seiler@vlsisj.uucp (%)
Organization: Compass Design Automation   San Jose, California
Lines: 53

In article <4799@gmdzi.gmd.de>, strobl@gmdzi.gmd.de (Wolfgang Strobl) writes:
|> Charlie.Mingo@p4218.f421.n109.z1.FidoNet.Org (Charlie Mingo) writes:
|> 
|> >mariusk@Lise.Unit.NO (Marius Kjeldahl) writes:
|> 
|> >MK> 1. Usually RAM is faster than ROM, thats why they incorporate things
like 
|> >MK> shadowram and so on.
|> 
|> >     RAM may be slightly faster than ROM in the MS-DOS world, but on Macs
the 
|> >opposite is true. ...
|> 
|> How that? What kind of ROMs are used in Macs?

I am surprised that RAM is faster than ROM in the IBM clone world.  What type of
ROM's do IBM clones use?  The types are:

   Mask Programmed ROM - fastest and largest memory type for a given geometry.
       The data is frozen in by metal layers added to the chip at the last
stage
        of processing.  Only practical if a large number of identical ROM's are
        to be made.

   PROM - programmed by blowing internal fuses.  Also fast but size is more
          limited.

   EPROM - These are programmed by zapping with pulses of the correct voltage
         and rise time.  If the package has a quartz window, they can be erased
         with UV light.  These are slow.

   EEPROM (electrically erasable read only memory) - currently with very
           limited size.  Used mainly to store a small amount of status
           information while the power is turned off.  Some interesting work in
           ferro-electric memorys may change this.

I suppose that IBM clones may use EPROM's which benefit by copying into RAM. 
The Mac uses mask programmed type, which are faster than static RAM's, let alone
dynamic RAM's.  That assumes the same technology is used ( an ECL RAM will be
faster than a p MOS mask programmed ROM ).  The big disadvantage of the mask
programmed type is a significant set up cost for a run.  EPROM has essentially
no set up cost.  However, after the fixed cost, mask programmed ROM are
cheaper.

  In addition, some Mac's have a built video display which uses the main RAM to
hold the display buffer.  This slows down RAM access when the CPU contends with
the video display.  ROM doesn't have to contend with the video so it is slightly
faster.  By the way, this does not apply to plug in video cards.

Bruce Seiler
seiler@compass-da.com
Disclaimer: Just because my parent company sells ROM's amd other IC's to Apple
        and PC chip sets to IBM doesn't PROVE I know what I'm talking about.