DNIX - History

History

ISC Systems Corporation (ISC) purchased the right to use DNIX in the late 1980s for use in its line of Motorola 68k-based banking computers. (ISC was later bought by Olivetti, and was in turn resold to Wang, which was then bought by Getronics. This corporate entity, most often referred to as 'ISC', has answered to a bewildering array of names over the years.) This code branch was the SVR2 compatible version, and received extensive modification and development at their hands. Notable features of this operating system were its support of demand paging, diskless workstations, multiprocessing, asynchronous I/O, the ability to mount processes (handlers) on directories in the file system, and message passing. Its real-time support consisted largely of internal event-driven queues rather than list search mechanisms (no 'thundering herd'), static process priorities in two classes (run to completion and timesliced), support for contiguous files (to avoid fragmentation of critical resources), and memory locking. The quality of the orthogonal asynchronous event implementation has yet to be equalled in current commercial operating systems, though some approach it. (The concept that has yet to be adopted is that the synchronous marshalling point of all the asynchronous activity itself could be asynchronous, ad infinitum. DNIX handled this with aplomb.) The asynchronous I/O facility obviated the need for Berkeley sockets select or SVR4's STREAMS poll mechanism, though there was a socket emulation library that preserved the socket semantics for backward compatibility. Another feature of DNIX was that none of the standard utilities (such as ps, a frequent offender) rummaged around in the kernel's memory to do their job. System calls were used instead, and this meant the kernel's internal architecture was free to change as required. The handler concept allowed network protocol stacks to be outside the kernel, which greatly eased development and improved overall reliability, though at a performance cost. It also allowed for foreign file systems to be user-level processes, again for improved reliability. The main file system, though it could have been (and once was) an external process, was pulled into the kernel for performance reasons. Were it not for this DNIX could well have been considered a microkernel, though it was not formally developed as such. Handlers could appear as any type of 'native' Unix file, directory structure, or device, and file I/O requests that the handler itself could not process could be passed off to other handlers, including the underlying one upon which the hander was mounted. Handler connections could also exist and be passed around independent of the filesystem, much like a pipe. One effect of this is that TTY-like 'devices' could be emulated without requiring a kernel-based pseudo terminal facility.

An example of where a handler saved the day was in ISC's diskless workstation support, where a bug in the implementation meant that using named pipes on the workstation could induce undesirable resource locking on the fileserver. A handler was created on the workstation to field accesses to the afflicted named pipes until the appropriate kernel fixes could be developed. This handler required approximately 5 kilobytes of code to implement, an indication that a non-trivial handler did not need to be large.

ISC also received the right to manufacture DIAB's DS90-10 and DS90-20 machines as its file servers. The multiprocessor DS90-20's, however, were too expensive for the target market and ISC designed its own servers and ported DNIX to them. ISC designed its own GUI-based diskless workstations for use with these file servers, and ported DNIX again. (Though ISC used Daisy workstations running Daisy DNIX to design the machines that would run DIAB's DNIX, there was negligible confusion internally as the drafting and layout staff rarely talked to the software staff. Moreover, the hardware design staff didn't use either system! The running joke went something like: "At ISC we build computers, we don't use them.") The asynchronous I/O support of DNIX allowed for easy event-driven programming in the workstations, which performed well even though they had relatively limited resources. (The GUI diskless workstation had a 7 MHz 68010 processor and was usable with only 512K of memory, of which the kernel consumed approximately half. Most workstations had 1 MB of memory, though there were later 2 MB and 4 MB versions, along with 10 MHz processors.) A full-blown installation could consist of one server (16 MHz 68020, 8 MB of RAM, and a 200 MB hard disk) and up to 64 workstations. Though slow to boot up, such an array would perform acceptably in a bank teller application. Besides the innate efficiency of DNIX, the associated DIAB C compiler was key to high performance. It generated particularly good code for the 68010, especially after ISC got done with it. (ISC also retargeted it to the Texas Instruments TMS34010 graphics coprocessor used in its last workstation.) The DIAB C compiler was, of course, used to build DNIX itself which was one of the factors contributing to its efficiency, and is still available (in some form) through Wind River Systems.

These systems are still in use as of this writing in 2006, in former Seattle-First National Bank branches now branded Bank of America. There may be, and probably are, other ISC customers still using DNIX in some capacity. Through ISC there was a considerable DNIX presence in Central and South America.