5 ms·

This is only based on playing around with it in a VM and poking at its source code after it was open sourced with a BSD license in 2015, but to me, Coherent see

by anyfoo 7y ago

This is only based on playing around with it in a VM and poking at its source code after it was open sourced with a BSD license in 2015, but to me, Coherent seemed like a quite well put together system. Enough that it made me a bit sad that it's now an OS of the past.

simonblack 7y ago
Coherent's misfortune was that it was released at the same time that Linux was. All through the 90s as I progressed from Coherent to AT&T Unix to Novell's Unixware to Sun's Solaris, I used to to look at Linux every six months or so. I was always gobsmacked at how quickly Linux (actually Gnu/Linux) was moving ahead in leaps and bounds. By the time that 2001 rolled around, it was time for me to put away my Solaris and switch to Linux fulltime.
- ecksii 7y ago
  While Linux would have certainly killed Coherent eventually, that's not quite the case. First Coherent was out long before Linux. Coh was around long enough for AT&T to have sent Dennis Ritchie to Chicago to inspect the code and evaluate it for copyright claims. Coherent ran on the PDP11 and on the 80286. Linux became a real force in the Unix market around 1998. MWC went out of business in Feb 1995. The first round of layoffs at MWC happened in Oct, 1994. A perfect storm of several things killed Coherent The two biggest problems were: The customers dinging Mark Williams Company in the newsgroup mainly complained about the lack of TCP/IP networking. This happened because MWC had done a customer pole to see what big feature should come next? TCP/IP or X11. X11 won. The real or perceived drop in quality of the product. This one is hard to explain. Coherent 3.10 and 4.0 had been solid V7 Unix clones with V7 sensibilities. When 4.2.05 shipped it included a really nasty disk driver bug that basically destroyed your file system beyond the ability of fsck to fix. The bug was triggered when your drive when into a very common thermal recalibration mode. This mode was rare or hadn't existed during the days of MFM/RLL/ESDI drives but became common with ATA drives especially as the market got flooded with cheap 504MB drives. While the bug was fixed somewhere between 4.2.10 and 4.2.14, the damage to Coherent's reputation was done.
  - nigel_bree 7y ago
    > The bug was triggered when your drive when into a very common thermal recalibration mode As the person responsible (alas), my specific recollection of this particular bug was that the root cause wasn't thermal recalibration, but rather UDMA signalling errors. Prior versions of Coherent using PIO mode had excruciatingly slow access, and when adding support for UDMA I also added support for the disk driver to recognise sequential access and issue multisector transfer requests; this boosted performance fairly massively, something like 3-4 times for some common things, and it was run for a fairly long time in-house and by beta testers with no trouble before it shipped. The problem though, was a small - literally one line - arithmetic error when the drive end of things reported a UDMA transfer error had occurred in the middle of a multisector operation; the error-handling code that set up a retry of the operation didn't compute the start kernel address correctly when a whole bunch of transfers had been merged (and some subset had worked). The primary problem with the UDMA modes was sensitivity to correct cable termination - see https://en.wikipedia.org/wiki/Parallel_ATA#Cable_select https://en.wikipedia.org/wiki/Parallel_ATA#Cable_select for some of that; basically, signal reflections from parallel ATA cable runs that didn't have terminating resistors made things electrically marginal and some systems would have really excessive numbers of UDMA CRC faults as a consequence, and given sufficiently high error rates and really bad timing that could end up polluting the buffer cache with stuff that was skewed by a sector :-( The big thing (on top of not having any in-house hardware that triggered this specific bug) was the sheer volume of work required for those releases, since getting from what was basically a fairly vanilla Seventh Edition UNIX to where it needed to be to start running large pieces of third-party code expecting POSIX was a big lift. Since there weren't many people, everyone was having to wear lots of hats; for instance, aside from kernel work I did a huge amount of work for POSIX.1 and .2 compatibility and on top of doing the underlying code changes (which ranged all over the system, particularly for some of the stuff we ran into Autotools scripts relying on) all of those needed documenting, too. [ Fred Butzen did amazing work writing the actual manpage text and making it really easy to understand - he justly deserved the credit for the quality of the manual in terms of its readability. But the scale of the changes needed to bring so many parts and pieces from V7 to POSIX meant lots and lots and lots of work trying to iterate over docs for technical accuracy at the same time as having to redesign all the affected parts and pieces. It was, in a word, exhausting. ]

by anyfoo 7y ago

simonblack 7y ago

Coherent's misfortune was that it was released at the same time that Linux was. All through the 90s as I progressed from Coherent to AT&T Unix to Novell's Unixware to Sun's Solaris, I used to to look at Linux every six months or so. I was always gobsmacked at how quickly Linux (actually Gnu/Linux) was moving ahead in leaps and bounds. By the time that 2001 rolled around, it was time for me to put away my Solaris and switch to Linux fulltime.

ecksii 7y ago
While Linux would have certainly killed Coherent eventually, that's not quite the case. First Coherent was out long before Linux. Coh was around long enough for AT&T to have sent Dennis Ritchie to Chicago to inspect the code and evaluate it for copyright claims. Coherent ran on the PDP11 and on the 80286. Linux became a real force in the Unix market around 1998. MWC went out of business in Feb 1995. The first round of layoffs at MWC happened in Oct, 1994. A perfect storm of several things killed Coherent The two biggest problems were: The customers dinging Mark Williams Company in the newsgroup mainly complained about the lack of TCP/IP networking. This happened because MWC had done a customer pole to see what big feature should come next? TCP/IP or X11. X11 won. The real or perceived drop in quality of the product. This one is hard to explain. Coherent 3.10 and 4.0 had been solid V7 Unix clones with V7 sensibilities. When 4.2.05 shipped it included a really nasty disk driver bug that basically destroyed your file system beyond the ability of fsck to fix. The bug was triggered when your drive when into a very common thermal recalibration mode. This mode was rare or hadn't existed during the days of MFM/RLL/ESDI drives but became common with ATA drives especially as the market got flooded with cheap 504MB drives. While the bug was fixed somewhere between 4.2.10 and 4.2.14, the damage to Coherent's reputation was done.
- nigel_bree 7y ago
  > The bug was triggered when your drive when into a very common thermal recalibration mode As the person responsible (alas), my specific recollection of this particular bug was that the root cause wasn't thermal recalibration, but rather UDMA signalling errors. Prior versions of Coherent using PIO mode had excruciatingly slow access, and when adding support for UDMA I also added support for the disk driver to recognise sequential access and issue multisector transfer requests; this boosted performance fairly massively, something like 3-4 times for some common things, and it was run for a fairly long time in-house and by beta testers with no trouble before it shipped. The problem though, was a small - literally one line - arithmetic error when the drive end of things reported a UDMA transfer error had occurred in the middle of a multisector operation; the error-handling code that set up a retry of the operation didn't compute the start kernel address correctly when a whole bunch of transfers had been merged (and some subset had worked). The primary problem with the UDMA modes was sensitivity to correct cable termination - see https://en.wikipedia.org/wiki/Parallel_ATA#Cable_select https://en.wikipedia.org/wiki/Parallel_ATA#Cable_select for some of that; basically, signal reflections from parallel ATA cable runs that didn't have terminating resistors made things electrically marginal and some systems would have really excessive numbers of UDMA CRC faults as a consequence, and given sufficiently high error rates and really bad timing that could end up polluting the buffer cache with stuff that was skewed by a sector :-( The big thing (on top of not having any in-house hardware that triggered this specific bug) was the sheer volume of work required for those releases, since getting from what was basically a fairly vanilla Seventh Edition UNIX to where it needed to be to start running large pieces of third-party code expecting POSIX was a big lift. Since there weren't many people, everyone was having to wear lots of hats; for instance, aside from kernel work I did a huge amount of work for POSIX.1 and .2 compatibility and on top of doing the underlying code changes (which ranged all over the system, particularly for some of the stuff we ran into Autotools scripts relying on) all of those needed documenting, too. [ Fred Butzen did amazing work writing the actual manpage text and making it really easy to understand - he justly deserved the credit for the quality of the manual in terms of its readability. But the scale of the changes needed to bring so many parts and pieces from V7 to POSIX meant lots and lots and lots of work trying to iterate over docs for technical accuracy at the same time as having to redesign all the affected parts and pieces. It was, in a word, exhausting. ]