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From: John Larkin on 13 Jun 2010 11:28 On Sun, 13 Jun 2010 07:52:12 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: >On Jun 13, 2:09 am, Paul Keinanen <keina...(a)sci.fi> wrote: >> On Sat, 12 Jun 2010 09:56:27 -0700 (PDT), MooseFET >> >> <kensm...(a)rahul.net> wrote: >> >Way back in the tape drive days, seismic systems wrote their data >> >onto tape. They servoed the speed of the drive so that the ADC >> >output would be matched so that ony a very little buffering was >> >needed. For marine surveys, the length of time a ship could stay >> >at sea was set by the number of tapes the ship could carry a crew >> >of perhaps 3 people would spend all day and night changing the >> >tapes. The machine would cycle between 2 or 3 drives. >> >> I have never used 1200 BPI tapes, but at least the 800 BPI systems >> were extremely picky about keeping the read/write heads perpendicular >> to the tape motion. >> >> With multiple writing drives, you really had to keep the heads aligned >> the same way on all drives, unless you wanted to realign the read head >> after each tape :-) >> >> At 1600 BPI, each tape channel was individually clocked, so there was >> not so much need to keep the R/W head aligned. > >There were lots of odd sorts of drives in the early days: > >There were also the drives called "incremental" drives where the tape >was moved by a stepper. Each bit group was recorded on command. > >There are "analog" drives that where basically audio tape recorders. >Some of these were FM where the signal was modulated onto a carrier. >Some used other modulations. > >There were tapes with strange numbers of tracks like 13 and 25. DECtape was cool. Bidirectional, block-structured, fun to watch. John
From: MooseFET on 13 Jun 2010 12:03 On Jun 13, 11:28 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Sun, 13 Jun 2010 07:52:12 -0700 (PDT), MooseFET > > > > <kensm...(a)rahul.net> wrote: > >On Jun 13, 2:09 am, Paul Keinanen <keina...(a)sci.fi> wrote: > >> On Sat, 12 Jun 2010 09:56:27 -0700 (PDT), MooseFET > > >> <kensm...(a)rahul.net> wrote: > >> >Way back in the tape drive days, seismic systems wrote their data > >> >onto tape. They servoed the speed of the drive so that the ADC > >> >output would be matched so that ony a very little buffering was > >> >needed. For marine surveys, the length of time a ship could stay > >> >at sea was set by the number of tapes the ship could carry a crew > >> >of perhaps 3 people would spend all day and night changing the > >> >tapes. The machine would cycle between 2 or 3 drives. > > >> I have never used 1200 BPI tapes, but at least the 800 BPI systems > >> were extremely picky about keeping the read/write heads perpendicular > >> to the tape motion. > > >> With multiple writing drives, you really had to keep the heads aligned > >> the same way on all drives, unless you wanted to realign the read head > >> after each tape :-) > > >> At 1600 BPI, each tape channel was individually clocked, so there was > >> not so much need to keep the R/W head aligned. > > >There were lots of odd sorts of drives in the early days: > > >There were also the drives called "incremental" drives where the tape > >was moved by a stepper. Each bit group was recorded on command. > > >There are "analog" drives that where basically audio tape recorders. > >Some of these were FM where the signal was modulated onto a carrier. > >Some used other modulations. > > >There were tapes with strange numbers of tracks like 13 and 25. > > DECtape was cool. Bidirectional, block-structured, fun to watch. I still have a tape. It was used on a PDP-12. The PDP-12 was a machine with 2 instruction sets. I was a PDP-8 and also a machine called a Link. An I/O operation would flip it over to a Link Mode and back.
From: Paul Keinanen on 13 Jun 2010 12:49 On Sun, 13 Jun 2010 07:52:12 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: >On Jun 13, 2:09 am, Paul Keinanen <keina...(a)sci.fi> wrote: >> On Sat, 12 Jun 2010 09:56:27 -0700 (PDT), MooseFET >> >> I have never used 1200 BPI tapes, but at least the 800 BPI systems >> were extremely picky about keeping the read/write heads perpendicular >> to the tape motion. >> >> With multiple writing drives, you really had to keep the heads aligned >> the same way on all drives, unless you wanted to realign the read head >> after each tape :-) >> >> At 1600 BPI, each tape channel was individually clocked, so there was >> not so much need to keep the R/W head aligned. > >There were lots of odd sorts of drives in the early days: > >There were also the drives called "incremental" drives where the tape >was moved by a stepper. Each bit group was recorded on command. > >There are "analog" drives that where basically audio tape recorders. >Some of these were FM where the signal was modulated onto a carrier. >Some used other modulations. > >There were tapes with strange numbers of tracks like 13 and 25. and 42 tracks. These were all instrumentation recorders, not computer tapes. All 1/2 inch computer tapes I have ever seen were 7 or 9 track. These drives had vertical tape columns on both sides of the R/W head. The vacuum at the bottom of these columns kept the tape firmly at the R/W heads even during high acceleration start/stop operations, in which the heavy tape reel motors could not have followed.
From: John Larkin on 13 Jun 2010 14:19 On Sun, 13 Jun 2010 09:03:27 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: >On Jun 13, 11:28 pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Sun, 13 Jun 2010 07:52:12 -0700 (PDT), MooseFET >> >> >> >> <kensm...(a)rahul.net> wrote: >> >On Jun 13, 2:09 am, Paul Keinanen <keina...(a)sci.fi> wrote: >> >> On Sat, 12 Jun 2010 09:56:27 -0700 (PDT), MooseFET >> >> >> <kensm...(a)rahul.net> wrote: >> >> >Way back in the tape drive days, seismic systems wrote their data >> >> >onto tape. They servoed the speed of the drive so that the ADC >> >> >output would be matched so that ony a very little buffering was >> >> >needed. For marine surveys, the length of time a ship could stay >> >> >at sea was set by the number of tapes the ship could carry a crew >> >> >of perhaps 3 people would spend all day and night changing the >> >> >tapes. The machine would cycle between 2 or 3 drives. >> >> >> I have never used 1200 BPI tapes, but at least the 800 BPI systems >> >> were extremely picky about keeping the read/write heads perpendicular >> >> to the tape motion. >> >> >> With multiple writing drives, you really had to keep the heads aligned >> >> the same way on all drives, unless you wanted to realign the read head >> >> after each tape :-) >> >> >> At 1600 BPI, each tape channel was individually clocked, so there was >> >> not so much need to keep the R/W head aligned. >> >> >There were lots of odd sorts of drives in the early days: >> >> >There were also the drives called "incremental" drives where the tape >> >was moved by a stepper. Each bit group was recorded on command. >> >> >There are "analog" drives that where basically audio tape recorders. >> >Some of these were FM where the signal was modulated onto a carrier. >> >Some used other modulations. >> >> >There were tapes with strange numbers of tracks like 13 and 25. >> >> DECtape was cool. Bidirectional, block-structured, fun to watch. > >I still have a tape. It was used on a PDP-12. The PDP-12 was a >machine >with 2 instruction sets. I was a PDP-8 and also a machine called a >Link. >An I/O operation would flip it over to a Link Mode and back. > > Yeah that was weird. The 8 was a 2's complement machine, and Linc was sign-magnitude! John
From: MooseFET on 14 Jun 2010 02:52
On Jun 14, 2:19 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Sun, 13 Jun 2010 09:03:27 -0700 (PDT), MooseFET > > > > <kensm...(a)rahul.net> wrote: > >On Jun 13, 11:28 pm, John Larkin > ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> On Sun, 13 Jun 2010 07:52:12 -0700 (PDT), MooseFET > > >> <kensm...(a)rahul.net> wrote: > >> >On Jun 13, 2:09 am, Paul Keinanen <keina...(a)sci.fi> wrote: > >> >> On Sat, 12 Jun 2010 09:56:27 -0700 (PDT), MooseFET > > >> >> <kensm...(a)rahul.net> wrote: > >> >> >Way back in the tape drive days, seismic systems wrote their data > >> >> >onto tape. They servoed the speed of the drive so that the ADC > >> >> >output would be matched so that ony a very little buffering was > >> >> >needed. For marine surveys, the length of time a ship could stay > >> >> >at sea was set by the number of tapes the ship could carry a crew > >> >> >of perhaps 3 people would spend all day and night changing the > >> >> >tapes. The machine would cycle between 2 or 3 drives. > > >> >> I have never used 1200 BPI tapes, but at least the 800 BPI systems > >> >> were extremely picky about keeping the read/write heads perpendicular > >> >> to the tape motion. > > >> >> With multiple writing drives, you really had to keep the heads aligned > >> >> the same way on all drives, unless you wanted to realign the read head > >> >> after each tape :-) > > >> >> At 1600 BPI, each tape channel was individually clocked, so there was > >> >> not so much need to keep the R/W head aligned. > > >> >There were lots of odd sorts of drives in the early days: > > >> >There were also the drives called "incremental" drives where the tape > >> >was moved by a stepper. Each bit group was recorded on command. > > >> >There are "analog" drives that where basically audio tape recorders. > >> >Some of these were FM where the signal was modulated onto a carrier. > >> >Some used other modulations. > > >> >There were tapes with strange numbers of tracks like 13 and 25. > > >> DECtape was cool. Bidirectional, block-structured, fun to watch. > > >I still have a tape. It was used on a PDP-12. The PDP-12 was a > >machine > >with 2 instruction sets. I was a PDP-8 and also a machine called a > >Link. > >An I/O operation would flip it over to a Link Mode and back. > > Yeah that was weird. The 8 was a 2's complement machine, and Linc was > sign-magnitude! Yes, the Link ALU was complete with the end around carry. IIRC, the Link addressed 2K word pages instead of the 4K "fields" of the PDP-8 part. The OS such as it was had exactly one error message "no". |