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- Newsgroups: comp.sys.mac.hardware
- Path: sparky!uunet!decwrl!pa.dec.com!rdg.dec.com!decvax.dec.com!decvax!strange
- From: strange@zk3.dec.com (Steve Strange)
- Subject: Re: 25MHz IIsi and my engineering friend
- In-Reply-To: eepmatt@casbah.acns.nwu.edu's message of Sun, 15 Nov 1992 12:17:08 GMT
- Message-ID: <STRANGE.92Nov15114832@squeeze.dec.com>
- Sender: usenet@decvax.dec.com (Usenet News System)
- Nntp-Posting-Host: squeeze.zk3.dec.com
- Organization: Digital Equipment Corp.
- References: <1992Nov15.121708.24693@news.acns.nwu.edu>
- Date: 15 Nov 92 11:48:32
- Lines: 55
-
- In article <1992Nov15.121708.24693@news.acns.nwu.edu> eepmatt@casbah.acns.nwu.edu (Matthew Friedman) writes:
-
- 1. (The Biggie First) He said that increasing the clockspeed of a machine
- should _NOT_ increase heat in a microprocessor if that chip is designed to
- handle the increase. He said that an increase in heat would _only_ occur if
- there were capacitances in the chip, or "wires" that were too close to each
- other to handle the increased frequency and "energy" was jumping from one to
- another. He said it was too difficult to explain why an increase in clockspeed
- would not cause an increase in heat ina properly designed chip. (My being a
- film major did not make things easier for him!)
-
- This is incorrect. A CMOS chip *will* generate more heat if run at a
- high clock rate. CMOS transistors only draw significant power when
- they are are switching from one state to another (i.e. from logical
- "1" to "0" or back again). If you increase the rate at which these
- transitions take place, more power will be drawn. That power has to
- go somewhere -- it all ends up going to heat. If the chip is run at a
- high enough frequency that it gets hot enough to damage itself, it
- needs a heat sink. All the heat sink does is reduce the temperature
- at which an equilibrium is reached between the generation of heat in
- the chip and the radiation of heat from the chip and heat sink.
-
- So, if this is true, the increase in heat would seem to be an
- indication that the microprocessor is _NOT_ suitable for higher speeds.
-
- As long as the heat sink keeps the operating temperature low enough,
- the higher speed is not a problem. Unless, of course, the chip
- doesn't logically function properly due to propagation delays in the
- chip or, much more likely, in the wires leading to and from the chip.
-
- 2. The only damage this procedure could do, he said, would be through the
- increased heat. So attaching a heat sink would make it safe. All the other
- problems he said would be data errors, and could be fixed by swapping back
- to the original clockspeed.
-
- I agree totally with this.
-
- 3. He told me it is a common practice in ibm's to upgrade to a higher
- clockspeed simply by swapping to a new microprocessor (apparently theirs
- include their own timing crystals.) This would suggest
- that the rest of the machine is safe from physical damage, even if an apple
- is not an ibm.
-
- Sounds reasonable to me.
-
-
- Steve
-
- --
- +---------------------------------------------------------------------------+
- | Steve Strange | Opinions expressed are my own and not |
- | Digital Equipment Corp. | necessarily those of my employer, or |
- | Nashua, NH 03062-2698 | of anyone else, for that matter. |
- | strange@zk3.dec.com | |
- +---------------------------------------------------------------------------+
-