test-drb November 2008

test-drb@ccmp.vtda.org

181 participants
235 discussions

by roger.holmes＠microspot.co.uk

> I have no idea about the material, but I can tell you about one application method you may not have considered. I have mentioned it here before but maybe you have joined the list recently. Similar drums were made by ICT/ICL from 1962 to 1965 for the 1300 series, and probably for the 1200 series drum based computers in the 50s. They too had fixed heads with set screw adjustment, which was carried out by monitoring the pressure of compressed air blown through a venturi in each head while moving an Allen screw. The 1300 drums were 12000 48bit word capacity, driven by a 3/4 horsepower motor geared up to 5240rpm at the drum spindle for lower access times. After many experiments they found they could not beat the human hand applying a magnetisable compound like a potter making a pot. Sounds very low tech but apparently it works, and I have drums which have not been touched since manufacture and they still work 46 years on. Of course for you, low tech could be a bonus as it means low cost. Maybe your local educational establishment has a skilled potter who could do a great job for a reasonable price, or just for interest. > The drum is quite low density, and does not have air bearing heads. > The head heights are actually adjustable with a bunch of set screws. > The heads themselves are also pretty big. This is a late 1950s drum, > not a 1970s era hard disk - there is a world of difference. I would > bet the heads ride a few thousands above the surface. > > The whole assembly is in a very rigid cast chassis, driven by a > relatively low-frills AC motor, apparently. > > My thinking is that the drum could be recoated (this is assuming it is > indeed shot), and using the rigid cast chassis, ground down to a > smooth surface with a custom made tool. This is much like a "poor mans > wheel lathe" used on railroad wheels. As long as the bearings are > still pretty tight, there should be very little wobble between the > drum and chassis. With each head being adjustable for height, much > inaccuracy across the drum becomes fairly unimportant. Inaccuracy > around the drum is more of an issue, but I suspect it will not be too > bad if the correct tool material and magnetic coating is used, and the > drum ground down gently. I will ask my real machinist friends about > the tooling, as I doubt I (or any of us) could make it.

15 years, 4 months

AT&T 7300/3B1's (was: Re: Who is vintagecomputermuseum?)

by micheladam＠theedge.ca

Does anyone know of a 'bridge' converter that would allow a scsi disk to interface to an MFM controller? Michel Adam ----- Original Message ----- From: Dave McGuire <mcguire at neurotica.com> Date: Wednesday, November 19, 2008 8:38 am Subject: Re: AT&T 7300/3B1's (was: Re: Who is vintagecomputermuseum?) > On Aug 18, 2008, at 10:26 AM, Mark Tapley wrote: > > I'll hunt for mice. I don't think I kept a spare, but if I did, > > I'll let you know. > > [old message referring to 3B1 mice, I couldn't find mine] > > I found my 3B1 mice. I hope to get the machine running soon, > but > I seem to have a shortage of functional MFM drives. Ugh. > > -Dave > > -- > Dave McGuire > Port Charlotte, FL > > >

15 years, 4 months

Australian ex-DEC Director has large museum in his home

by legalize＠xmission.com

Slideshow: <http://tinyurl.com/6f7kte> -- "The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download <http://www.xmission.com/~legalize/book/download/index.html> Legalize Adulthood! <http://blogs.xmission.com/legalize/>

15 years, 4 months

Hard disk material

by wdonzelli＠gmail.com

It looks like sometime in the future I may need to rebuild a damaged magnetic drum. It has some scratches that may be too deep. As a brainstorm, I am wondering about recoating the surface. If I use refined iron oxide, what would I use as a fixer (glue)? What was typically used on early hard disk platters and drums? -- Will

15 years, 5 months

Hard disk material

by wbblair3＠yahoo.com

> (My brain wants to say it was "how to build a working digital > computer", but I could be wrong there). I wonder if anyone ever > actually built one that worked? :-) Your brain is not leading you astray. That's the book. Here's the PDF version: http://www.bitsavers.org/pdf/paperClipComputer/HowToBuildAWorkingDigitalCom…

15 years, 5 months

problem with listserv?

by chrise＠pobox.com

Hmm... I've sent a number of things to this list which have not ever shown up here. Curious if I can actually really post to the list...?? I also see that postings from others show up about 5 to 6 days after they post them. For example, yesterday 11/29, I received gobs of postings dated 11/24. There will be many days of silence and then all of a sudden I'll get a bunch of them all at once, that many days behind. cje -- Chris Elmquist mailto:chrise at pobox.com

15 years, 5 months

Sun people and keyboards

by dgriffi＠cs.csubak.edu

Does anyone here have pull with Sun Microsystems or know someone who does? I'm trying to get the right person jazzed up about the idea of a Type 7 keyboard built like a Model M. I've already emailed clickykeyboards.com about it and they'll do the engineering and design work for about $27k. A Type 7 sells brand new for around $50. I'm sure people would be more than willing to pay twice as much for a "Type 7m". -- David Griffith dgriffi at cs.csubak.edu A: Because it fouls the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail?

15 years, 5 months

Minimal CP-M SBC design

by lynchaj＠yahoo.com

________________________________ Hi, all, I was staring at an SBC I have here with a 6MHz Z-80, some ROM, some RAM, and a 26-pin off-board bus for some Z80-PIO boards (this thing was built as a multi-parallel-printer switcher). I've been musing about what it would take to boot CP/M up on this. For user I/O, I was planning on a console serial port and a terminal/terminal emulator. I have IM6402s on hand, but I'd be interested in hearing if certain other chips are preferred, based on what BIOS code is floating around out there. I also have a 16550, but I don't think I have any Z80-SIO chips handy. For mass storage, I was planning on either Compact Flash or an SD card. I think I've seen both as I googled around for modern SBCs. Any of the media I have lying around is plenty large enough (I even have some 4MB CFs and a 2.5MB full-sized PCMCIA flash card on hand). I am a little unclear, though, about how traditional CP/M systems were set up for ROM and RAM. Was it common to use a "shadow ROM" in low mem at reset, then have the BIOS live at the top of memory? How did 64K RAM CP/M machines handle the BIOS? Did they temporarily ghost the ROM on top of RAM until some bit of code could read ROM and write RAM then bank out the ROM? Since I think I "need" at least 48K of RAM, I was planning on a pair of 62256s. I could easily do 56K of RAM low and 8K of ROM high, I think, unless there's some other arrangement that's obvious to try for a simple design. I've never tried writing a BIOS for a CP/M machine, but my understanding is that things are modular enough that once you know what I/O chips you have and at what I/O addresses, for a straightforward, non-clever design, the coding is equally straightforward and non-clever (but please feel free to enlighten me if otherwise). Thanks for any tips, especially from anyone on the list who has ever rolled their own CP/M machine. -ethan -- Ethan Dicks, A-333-S Current South Pole Weather at 4-May-2008 at 19:40 Z South Pole Station PSC 468 Box 400 Temp -74.2 F (-59.0 C) Windchill -105.4 F (-76.4 C) APO AP 96598 Wind 7.4 kts Grid 77 Barometer 691.6 mb (10194 ft) Ethan.Dicks at usap.gov <http://www.classiccmp.org/mailman/listinfo/cctalk> http://penguincentral.com/penguincentral.html -----REPLY----- Hi Ethan, Funny you should mention the subject, I am working on a very similar project. Last year, I made a completely home brew Z80 computer with prototype boards. It is a fun project and you can definitely build your own CP/M computer from scratch. It really is not that hard. This year, I am remaking the design using manufactured PCBs. I recently got my first batch of prototype PCBs and have been building up and testing them. So far, I have gotten the CPU, ROM, RAM, UART, and most of the glue logic working and tested. It is not complete yet as I still need to wring out much of the hardware and have not even started on the PPI or RTC. However, last year I was able to boot the previous system into its monitor and even boot CP/M. CP/M used a 32K ROM drive for drive A:, a 448K RAM drive for drive B:. I implemented an IDE port and a hard disk for drive C:. Those all worked pretty good. I built but never tested a floppy drive interface. The whole system is pretty simple, uses plain 74LSxxx chips, no programmable parts (except the EPROM) or hard to get parts. No SMT or funky technologies, just plain through hole DIP chips. I have all the software and am presently going through the library reinstalling it on the new system. So far, I have most of the easy stuff working. I do have the RAMless monitor working and next will be the regular monitor. Finally it will be the CP/M system and the RTC software. Anyway, if your interested, I am keeping a small Google group of files and photos at: http://groups.google.com/group/n8vem Thanks! Andrew Lynch

15 years, 5 months

IDE <-> MFM

by aek＠bitsavers.org

> What is the minimum satisfactory sampling rate if one wanted to emulate an ST-412 > interface and have it RLL (2,7)-capable? 2x, assuming you regenerate the clock. With a digital DLL, the incoming clock would be on the order of 8x the maximum incoming frequency. The bitstream is not variable frequency. You can think of what is needed as the inverse of the read recovery circuit on the drive controller. The tricky part is generating the recirculating bit stream that you send as read data back from the simulated drive. It is expecting the data that it just wrote to be in the data read back on the next revolution. And you need one of these bitstreams for each head.

15 years, 5 months

SCSI identify command

by aek＠bitsavers.org

> Actually, it's not clear to me if any of the > bridges supported that command. I don't know of any MFM/RLL controllers that supported scsi inquire. ESDI was the first 5" drive interface to support geometry inquiry which is needed to make inquiry work w/o the host specifying the drive geometry to the bridge board.

15 years, 5 months

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test-drb November 2008