test-drb April 1999

test-drb@ccmp.vtda.org

170 participants
1190 discussions

by gareth.knight2＠which.net

Zane H. Healy wrote: >Last I checked OS/2 Warp V3 and V4 were both available. I've heard a new >version is actually in the works (despite the fact I used to be a huge OS/2 >fan I find that a little hard to believe). In its favour OS/2 does have one of the fastest implementations of Java 1. -- Gareth Knight Amiga Interactive Guide | ICQ No. 24185856 http://welcome.to/aig | "Shine on your star"

26 years

FM, MFM, and GCR channel codes (was Re: stepping machanism of Apple Disk ][ drive)

by CLASSICCMP＠trailing-edge.COM

>Dick wrote: >> One interesting thing about the Apple GCR modulation format is that it >> essentially was a "double-density" technique. >Tim wrote: >> Eric said the same thing, and I disagree with you both. To me (and all >I said no such thing. I said that Apple used FM for the address fields, >and that the GCR they used for data fields was more efficient than FM, and >less efficient than MFM. I think you're confused as to what I was disagreeing with, and that's probably my fault for not explaining myself more clearly. I was disagreeing with what I believe to be your assertion, Eric, that you can take any FM data channel, pump about 50% more data through it with GCR, and pump twice as much data through it with MFM. There are twice as many places in a MFM data stream where a transition *may* take place, as compared to a FM data stream at the same data rate. The maximum number of transitions per time remains the same. At first glance, this might lead you to believe that the bandwidth needed for a FM encoding that gives you a data rate of 250kHz will also support a MFM encoding at 500kHz. It isn't this simple; if you do a Fourier transform of the MFM stream you'll see that you do indeed more bandwidth for MFM. On the other hand, a GCR data stream over the same circuit will give you a data rate of 375 kHz or so (depending on the details of the GCR) without requiring more bandwidth than the 250kHz FM channel. (Admittedly the GCR distribution of energy in that bandwidth will be more even than the FM distribution of energy - but that's precisely why you're able to pump more data through.) -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology WWW: http://www.trailing-edge.com/ 7328 Bradley Blvd Voice: 301-767-5917 Bethesda, MD, USA 20817 Fax: 301-767-5927

26 years

What if,... early PCs (was: stepping machanism

by geoffrob＠stmarks.pp.catholic.edu.au

---------- > From: Sellam Ismail <dastar(a)ncal.verio.com> > To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> > Subject: Re: What if,... early PCs (was: stepping machanism > Date: Saturday, April 10, 1999 7:10 > Rumor has it the Model 1 design was stolen from a third party consultant > by a less than talented head engineer at Radio Shack, and purportedly made > into the production model, bugs and all, so its not surprising that other > RS hardware was designed shoddily. RS is colloquial for "Rat Sh-t" in Oz, They don't market under that name here, but as Tandy or Micronta. (Accurate product description though isn't it?) Cheers Geoff Roberts VK5KDR Computer Systems Manager Saint Marks College Port Pirie, South Australia geoffrob(a)stmarks.pp.catholic.edu.au

26 years

What if,... early PCs (was: stepping machanism

by edick＠idcomm.com

-----Original Message----- From: Fred Cisin (XenoSoft) <cisin(a)xenosoft.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Friday, April 09, 1999 5:34 PM Subject: Re: What if,... early PCs (was: stepping machanism >On Fri, 9 Apr 1999, Allison J Parent wrote: >> <Double density was NOT readily achievable in 1978. And the poor quality >> My dog, don't tell DEC that or intel. > >Sorry, I should have said that it was not readily achievable for RADIO >SHACK, not that it wasn't possible. It took RS a few more years before >they were ready to have MFM in one of their consumer level machines. >RS's early FM had some data separation problems; I assume that that was >due to trying to keep the cost too low? > The RS people had their heads wedged, probably due to politics. They used a strange mix of parts, seemingly cobbled together from various vendors' app notes. Their FDC used a TI TTL VCO, a Motorola phase detector, and a Western Digital controller chip. Additionally they used some wierd TI clock generator and some other stuff I couldn't justify. Their clock recovery circuit was pretty poor, i.e. poorer than average, and cost about 6x what I was used to seeing. Their dynamic memory handling wasn't any sort of slick, nor was their video circuit. They could have used a circuit similar to what the Xerox 820 had from day 1. It was an old design from a simple terminal and would freuently work on a modified TV set, which is all RS was shipping anyway. It's clear that there was politics and corruption at the top. Dick >

26 years

Mac Media Players

by roblwill＠usaor.net

Does anyone know of a MIDI / Media (wav?) player for a Mac that will run on a Mac Portable with System 7.5 and 4 MB RAM? Better yet, does anyone know of where (other than SUN Remarketing) to get a RAM upgrade for the Portable? ThAnX, -- -Jason Willgruber (roblwill(a)usaor.net) ICQ#: 1730318 <http://members.tripod.com/general_1>

26 years

stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5

by edick＠idcomm.com

Since I have several of the drives, I do, indeed have the service documents for the model 277 (single-sided) drive. The difference between FM and MFM is not the rate at which thd data and clocks are written to the drive, but rather, the modulation technique itself. Instead of haveing a discretely presented clock 180-degrees out of phase with the data window, it has an imbedded clock, in which, like manchester code, the data is shifted in phase from the clock. If there is a long string of ones, they are written in phase, one pulse per clock, while if there's a long string of zeroes, the zeroes are represented by a string of pulses 180 degrees out of phase , omitting the first and last pulses in order to avoid crowding them to such extent that it violates the maximal flux reversal density. As a result, you get a modulated waveform which contains both the data and the clock in it in such a way that you can write and read double the amount you can write and read using FM, since FM automatically consumes half the channel bandwidth for discrete clock pulses. It should come as no surprise that this works much like Manchester Code. Dick -----Original Message----- From: Tony Duell <ard(a)p850ug1.demon.co.uk> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Friday, April 09, 1999 4:44 PM Subject: Re: stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5 >> Actually, Persci floppy drives in 1976 or so were voice-coil (and quite >> a pain to maintain, even then - these days the glue that holds the >> optical graticules in place is often failing, and gluing and realigning >> from scratch is even harder, even with all the special Persci >> realignment jigs and electronic panels.) And a common modification > >Does anyone have the service manuals for these drives? I have one on my >old CASU S100 system, and although it's not failed yet, I'm sure I'll >have to fix it sometime. > >Are they any worse to maintain than RK05s, say? The overall design of the >positioner seems to be very similar. > >> >One interesting thing about the Apple GCR modulation format is that it >> >essentially was a "double-density" technique. >> >> Eric said the same thing, and I disagree with you both. To me (and all >> the tech pubs I've read) the density is how many flux transitions you can >> do per second (or revolution). GCR is a way of getting more real data with > >Hmm... Are you implying that conventional MFM double density is just FM >with a faster clock rate? Surely not. > >I thought the whole point of MFM was to reduce the number of flux >transitions per (user) data bit. An FM bit cell _always_ has a clock >transition, and may have a data transition as well. MFM removes some of >the 'wasted' clock transitions. > >> the same number of flux transitions. Apple GCR drives use single-density > >As, IMHO is MFM. > >-tony >

26 years

Heathkit H-8 questions

by fpp＠concentric.net

I saw a H-8 on eBay tonight. What year were these made? The year was about 1976-77. Saw it at the Heathkit store in LA. That and the 16 convinced them to go full steam into computers and rest is out of business history!

26 years

Don Lancaster was Re: Ebay Mark-8 Plans

by rigdonj＠intellistar.net

At 04:27 PM 4/9/99, Dave wrote: > >The seller also has the RE TVT plans by Don Lancaster. Speaking of Don Lancaster, has anyone asked him to speak at VCF or told him about this list? He's been involved with the home PCs since the beginning and is probably a wealth of infomation. Joe

26 years

Heathkit H-8 questions

by bluoval＠mindspring.com

I saw a H-8 on eBay tonight. What year were these made? What could one do with it? From the photo it has a 16 key keypad, numbers 1-9 and the math symbols, decimal point, and 2 others i can't make out. What are those 2 keys? I'm not trying to buy it, I wouldn't know what to do with it even if i did. just curious. TIA.

26 years

Timonium Hamfest

by geoffrob＠stmarks.pp.catholic.edu.au

> From: Uncle Roger <sinasohn(a)ricochet.net> > To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> > Subject: RE: Timonium Hamfest > Date: Wednesday, April 07, 1999 1:08 > Dysania: (n) an inability to function early in the morning. > > I've got it bad That makes two of us. Had it long as I can remember. Didn't know there was a name for it. You learn something every day.... Cheers Geoff VK5KDR

26 years

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test-drb April 1999