A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
A real-time operating system is an operating system intended to serve real-time application requests.A key characteristic of a RTOS is the level of its consistency concerning the amount of time it takes to accept and complete an application's task; the variability is jitter...
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
Dataindustrier AB or DIAB was a Swedish computer engineering and manufacturing firm, founded in 1970 by Lars Karlsson and active in the 1970s through 1990s. The company's first product was a board-based computer centered around a specific bus named Data Board 4680. This unit was used for automatic...
(DIAB). A version called ABCenix was also developed for the ABC1600 computer from Luxor. (Daisy Systems
Daisy Systems
Daisy Systems Corporation incorporated in 1981 in Mountain View, California, was a computer-aided engineering, CAE, company, a pioneer in the Electronic design automation industry....
also had something called Daisy DNIX on some of their CAD
Computer-aided design
Computer-aided design , also known as computer-aided design and drafting , is the use of computer technology for the process of design and design-documentation. Computer Aided Drafting describes the process of drafting with a computer...
workstations. It was unrelated to DIAB's product.)
History
ISC Systems Corporation (ISC) purchased the right to use DNIX in the late 1980s for use in its line of Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
The Motorola 680x0/m68000/68000 is a family of 32-bit CISC microprocessors. During the 1980s and early 1990s, they were popular in personal computers and workstations and were the primary competitors of Intel's x86 microprocessors...
-based banking computers. (ISC was later bought by Olivetti
Olivetti
Olivetti S.p.A. is an Italian manufacturer of computers, printers and other business machines.- Founding :The company was founded as a typewriter manufacturer in 1908 in Ivrea, near Turin, by Camillo Olivetti. The firm was mainly developed by his son Adriano Olivetti...
Wang may refer to:Name:* Wang , one of two surnames with distinct Chinese characters.* Titles in Chinese nobility* A title in Korean nobility* A title in Mongolian nobilityPlaces:* Wang River in Thailand...
Getronics N.V. is a company, subsidiary of the Dutch IT & Telecommunications firm KPN since October 2007, focused on creating value for IT Workspace Management Services, Applications & Software Development Services...
. 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
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
In computer operating systems, demand paging is an application of virtual memory. In a system that uses demand paging, the operating system copies a disk page into physical memory only if an attempt is made to access it...
Multiprocessing is the use of two or more central processing units within a single computer system. The term also refers to the ability of a system to support more than one processor and/or the ability to allocate tasks between them...
Asynchronous I/O, or non-blocking I/O, is a form of input/output processing that permits other processing to continue before the transmission has finished....
, the ability to mount processes (handlers) on directories in the file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
Message passing in computer science is a form of communication used in parallel computing, object-oriented programming, and interprocess communication. In this model, processes or objects can send and receive messages to other processes...
A real-time operating system is an operating system intended to serve real-time application requests.A key characteristic of a RTOS is the level of its consistency concerning the amount of time it takes to accept and complete an application's task; the variability is jitter...
support consisted largely of internal event-driven
Event-driven
Event driven may refer to:The term event-driven refers to a methodology that focuses on events and event dependencies.Examples include:* Event-driven finite-state machine, finite-state machine where the transition from one state to another is triggered by an event or a message* 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
Fragmentation (computer)
In computer storage, fragmentation is a phenomenon in which storage space is used inefficiently, reducing storage capacity and in most cases reducing the performance. The term is also used to denote the wasted space itself....
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
Berkeley sockets
The Berkeley sockets application programming interface comprises a library for developing applications in the C programming language that perform inter-process communication, most commonly for communications across a computer network....
In computer networking, STREAMS is the native framework in Unix System V for implementing character devices.STREAMS was designed as a modular architecture for implementing full-duplex I/O between kernel or user space processes and device drivers. Its most frequent uses have been in developing...
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
Microkernel
In computer science, a microkernel is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system . These mechanisms include low-level address space management, thread management, and inter-process communication...
, 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
Anonymous pipe
In computer science, an anonymous pipe is a simplex FIFO communication channel that may be used for one-way interprocess communication . An implementation is often integrated into the operating system's file IO subsystem...
. One effect of this is that TTY-like 'devices' could be emulated without requiring a kernel-based Pseudo terminal
Pseudo terminal
In some operating systems, including Unix, a pseudo terminal is a pseudo-device pair that provides a text terminal interface without an associated device, such as a virtual console, computer terminal or serial port...
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 pipe
Named pipe
In computing, a named pipe is an extension to the traditional pipe concept on Unix and Unix-like systems, and is one of the methods of inter-process communication. The concept is also found in Microsoft Windows, although the semantics differ substantially...
s 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 kilobyte
Kilobyte
The kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
s of code to implement, an indication that a non-trivial handler did not need to be large.
Diab is a village in the Bassar Prefecture in the Kara Region of north-western Togo.-External links:**...
'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
Gui
Gui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...
-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
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
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
Bank teller
A teller is an employee of a bank who deals directly with most customers. In some places, this employee is known as a cashier. Most teller jobs require cash handling experience and a high school diploma. Most banks provide on the job training....
application. Besides the innate efficiency of DNIX, the associated DIAB
Diab
Diab is a village in the Bassar Prefecture in the Kara Region of north-western Togo.-External links:**...
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
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
The TMS34010 was the first programmable graphics processor integrated circuit . First silicon was working at Texas Instruments in Houston in December 1985, and first shipment was to IBM's workstation facility in Kingston, New York, in January 1986...
graphics coprocessor used in its last workstation.) The DIAB
Diab
Diab is a village in the Bassar Prefecture in the Kara Region of north-western Togo.-External links:**...
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
Wind River Systems
Wind River Systems, Inc. is a company providing embedded systems, development tools for embedded systems, middleware, and other types of software. The company was founded in Berkeley, California in 1981 by Jerry Fiddler and David Wilner. On June 4, 2009, Wind River announced that Intel had bought...
.
These systems are still in use as of this writing in 2006, in former Seattle-First National Bank branches now branded Bank of America
Bank of America
Bank of America Corporation, an American multinational banking and financial services corporation, is the second largest bank holding company in the United States by assets, and the fourth largest bank in the U.S. by market capitalization. The bank is headquartered in Charlotte, North Carolina...
. 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
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
.
Asynchronous Events
DNIX's native system call was the dnix(2) library function, analogous to the standard Unix unix(2) or syscall(2) function. It took multiple arguments, the first of which was a function code. Semantically this single call provided all appropriate Unix functionality, though it was syntactically different from Unix and had, of course, numerous DNIX-only extensions.
DNIX function codes were organized into two classes: Type 1 and Type 2. Type 1 commands were those that were associated with I/O activity, or anything that could potentially cause the issuing process to block. Major examples were F_OPEN, F_CLOSE, F_READ, F_WRITE, F_IOCR, F_IOCW, F_WAIT, and F_NAP. Type 2 were the remainder, such as F_GETPID, F_GETTIME, etc. They could be satisfied by the kernel itself immediately.
In computer programming, a file descriptor is an abstract indicator for accessing a file. The term is generally used in POSIX operating systems...
called a trap queue had to have been created via the Type 2 opcode F_OTQ. A Type 1 call would have the F_NOWAIT bit OR-ed with its function value, and one of the additional parameters to dnix(2) was the trap queue file descriptor. The return value from an asynchronous call was not the normal value but a kernel-assigned identifier. At such time as the asynchronous request completed, a read(2) (or F_READ) of the trap queue file descriptor would return a small kernel-defined structure containing the identifier and result status. The F_CANCEL operation was available to cancel any asynchronous operation that hadn't yet been completed, one of its arguments was the kernel-assigned identifier. (A process could only cancel requests that were currently owned by itself. The exact semantics of cancellation was up to each request's handler, fundamentally it only meant that any waiting was to be terminated. A partially completed operation could be returned.) In addition to the kernel-assigned identifier, one of the arguments given to any asynchronous operation was a 32-bit user-assigned identifier. This most often referenced a function pointer to the appropriate subroutine that would handle the I/O completion method, but this was merely convention. It was the entity that read the trap queue elements that was responsible for interpreting this value.
struct itrq { /* Structure of data read from trap queue. */
short it_stat; /* Status */
short it_rn; /* Request number */
long it_oid; /* Owner ID given on request */
long it_rpar; /* Returned parameter */
};
Of note is that the asynchronous events were gathered via normal file descriptor read operations, and that such reading was itself capable of being made asynchronous. This had implications for semi-autonomous asynchronous event handling packages that could exist within a single process. (DNIX 5.2 did not have lightweight processes or threads.) Also of note is that any potentially blocking operation was capable of being issued asynchronously, so DNIX was well equipped to handle many clients with a single server process. A process was not restricted to having only one trap queue, so I/O requests could be grossly prioritized in this way.
Compatibility
In addition to the native dnix(2) call, a complete set of 'standard' libc interface calls was available. open(2), close(2), read(2), write(2), etc. Besides being useful for backwards compatibility, these were implemented in a binary-compatible manner with the NCR Tower
NCR Corporation
NCR Corporation is an American technology company specializing in kiosk products for the retail, financial, travel, healthcare, food service, entertainment, gaming and public sector industries. Its main products are self-service kiosks, point-of-sale terminals, automated teller machines, check...
computer, so that binaries compiled for it would run unchanged under DNIX. The DNIX kernel had two trap dispatchers internally, one for the DNIX method and one for the Unix method. Choice of dispatcher was up to the programmer, and using both interchangeably was acceptable. Semantically they were identical wherever functionality overlapped. (In these machines the 68000 trap #0 instruction was used for the unix(2) calls, and the trap #4 instruction for dnix(2). The two trap handlers were really quite similar, though the [usually hidden] unix(2) call held the function code in the processor's D0 register, whereas dnix(2) held it on the stack with the rest of the parameters.)
DNIX 5.2 had no networking protocol stacks internally (except for the thin X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
The protocol stack is an implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them....
added by ISC for use by its diskless workstation support package), all networking was conducted by reading and writing to Handlers. Thus, there was no socket
Berkeley sockets
The Berkeley sockets application programming interface comprises a library for developing applications in the C programming language that perform inter-process communication, most commonly for communications across a computer network....
mechanism, but a libsocket(3) existed that used asynchronous I/O to talk to the TCP/IP handler. The typical Berkeley-derived networking program could be compiled and run unchanged (modulo the usual Unix porting
Porting
In computer science, porting is the process of adapting software so that an executable program can be created for a computing environment that is different from the one for which it was originally designed...
problems), though it might not be as efficient as an equivalent program that used native asynchronous I/O.
Handlers
Under DNIX, a process could be used to handle I/O requests and to extend the filesystem. Such a process was called a Handler, and was a major feature of the operating system. A handler was defined as a process that owned at least one request queue, a special file descriptor that was procured in one of two ways: with a F_ORQ or a F_MOUNT call. The former invented an isolated request queue, one end of which was then typically handed down to a child process. (The network remote execution programs, of which there were many, used this method to provide standard I/O paths to their children.) The latter hooked into the filesystem so that file I/O requests could be adopted by handlers. (The network login programs, of which there were even more, used this method to provide standard I/O paths to their children, as the semantics of logging in under Unix requires a way for multiple perhaps-unrelated processes to horn in on the standard I/O path to the operator.) Once mounted on a directory in the filesystem, the handler then received all I/O calls to that point.
A handler would then read small kernel-assigned request data structures from the request queue. (Such reading could be done synchronously or asynchronously as the handler's author desired.) The handler would then do whatever each request required to be satisfied, often using the DNIX F_UREAD and F_UWRITE calls to read and write into the request's data space, and then would terminate the request appropriately using F_TERMIN. A privileged handler could adopt the permissions of its client for individual requests to subordinate handlers (such as the filesystem) via the F_T1REQ call, so it didn't need to reproduce the subordinate's permission scheme. If a handler was unable to complete a request itself, the F_PASSRQ function could be used to pass I/O requests from one handler to another. A handler could perform part of the work requested before passing the rest on to another handler. It was very common for a handler to be state-machine oriented so that requests it was fielding from a client were all done asynchronously. This allowed for a single handler to field requests from multiple clients simultaneously without them blocking each other unnecessarily. Part of the request structure was the process ID and its priority so that a handler could choose what to work on first based upon this information, there was no requirement that work be performed in the order it was requested. To aid in this, it was possible to poll both request and trap queues to see if there was more work to be considered before buckling down to actually do it.
struct ireq { /* Structure of incoming request */
short ir_fc; /* Function code */
short ir_rn; /* Request number */
long ir_opid; /* Owner ID that you gave on open or mount */
long ir_bc; /* Byte count */
long ir_upar; /* User parameter */
long ir_rad; /* Random address */
ushort ir_uid; /* User ID */
ushort ir_gid; /* User group */
time_t ir_time; /* Request time */
ulong ir_nph;
ulong ir_npl; /* Node and process ID */
};
There was no particular restriction on the number of request queues a process could have. This was used to provide networking facilities to chroot
Chroot
A chroot on Unix operating systems is an operation that changes the apparent root directory for the current running process and its children. A program that is run in such a modified environment cannot name files outside the designated directory tree. The term "chroot" may refer to the chroot...
jails, for example.
Examples
To give some appreciation of the utility of handlers, at ISC handlers existed for:
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....
/ISO9660
disk image files
RAM disk (for use with write-protected boot disks)
DNET is a proprietary software suite of network protocols created by DIAB, originally deployed on their Databoard products. It was based upon X.25, which was particularly popular in European telecommunications circles at that time...
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
Local Area Transport is a non-routable networking technology developed by Digital Equipment Corporation to provide connection between the DECserver 90, 100, 200, 300, 500, 700 and DECserver 900 terminal servers and Digital's VAX and Alpha and MIPS_architecture host computers via Ethernet, giving...
AppleTalk is a proprietary suite of protocols developed by Apple Inc. for networking computers. It was included in the original Macintosh released in 1984, but is now unsupported as of the release of Mac OS X v10.6 in 2009 in favor of TCP/IP networking...
DNET is a proprietary software suite of network protocols created by DIAB, originally deployed on their Databoard products. It was based upon X.25, which was particularly popular in European telecommunications circles at that time...
DNET is a proprietary software suite of network protocols created by DIAB, originally deployed on their Databoard products. It was based upon X.25, which was particularly popular in European telecommunications circles at that time...
Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communications facility using a virtual terminal connection...
rlogin is a software utility for Unix-like computer operating systems that allows users to log in on another host via a network, communicating via TCP port 513.It was first distributed as part of the 4.2BSD release....
DNET is a proprietary software suite of network protocols created by DIAB, originally deployed on their Databoard products. It was based upon X.25, which was particularly popular in European telecommunications circles at that time...
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
A packet assembler/disassembler, abbreviated PAD is a communications device which provides multiple asynchronous terminal connectivity to an X.25 network or host computer. It collects data from a group of terminals and places the data into X.25 packets...
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
Local Area Transport is a non-routable networking technology developed by Digital Equipment Corporation to provide connection between the DECserver 90, 100, 200, 300, 500, 700 and DECserver 900 terminal servers and Digital's VAX and Alpha and MIPS_architecture host computers via Ethernet, giving...
DNET is a proprietary software suite of network protocols created by DIAB, originally deployed on their Databoard products. It was based upon X.25, which was particularly popular in European telecommunications circles at that time...
In computing, xterm is the standard terminal emulator for the X Window System. A user can have many different invocations of xterm running at once on the same display, each of which provides independent input/output for the process running in it .xterm originated prior to the X Window System...
-like)
document (passbook) printer
dmap (ruptime analog)
windowmac (GUI gateway to Macintosh)
system patches
named pipe handler
ISC's Extensions
ISC purchased both 5.2 (SVR2 compatible) and 5.3 (SVR3 compatible) versions of DNIX. At the time of purchase, DNIX 5.3 was still undergoing development at DIAB
Diab
Diab is a village in the Bassar Prefecture in the Kara Region of north-western Togo.-External links:**...
so DNIX 5.2 was what was deployed. Over time, ISC's engineers incorporated most of their 5.3 kernel's features into 5.2, primarily shared memory
Shared memory
In computing, shared memory is memory that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Depending on context, programs may run on a single processor or on multiple separate processors...
In computing, Inter-process communication is a set of methods for the exchange of data among multiple threads in one or more processes. Processes may be running on one or more computers connected by a network. IPC methods are divided into methods for message passing, synchronization, shared...
, so there was some divergence of features between DIAB
Diab
Diab is a village in the Bassar Prefecture in the Kara Region of north-western Togo.-External links:**...
and ISC's versions of DNIX. DIAB's 5.3 likely went on to contain more SVR3 features than ISC's 5.2 ended up with. Also, DIAB went on to DNIX 5.4, a SVR4 compatible OS.
At ISC, developers considerably extended their version of DNIX 5.2 (only listed are features involving the kernel itself) based upon both their needs and the general trends of the Unix industry:
Diskless workstation support. The workstation's kernel filesystem was removed, and replaced with an X.25-based Ethernet communications stub. The file server's kernel was also extended with a mating component that received the remote requests and handed them to a pool of kernel processes for service, though a standard handler could have been written to do this. (Later in its product lifecycle, ISC deployed standard SVR4-based Unix servers in place of the DNIX servers. These used X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
In computer networking, STREAMS is the native framework in Unix System V for implementing character devices.STREAMS was designed as a modular architecture for implementing full-duplex I/O between kernel or user space processes and device drivers. Its most frequent uses have been in developing...
and a custom-written file server program. In spite of the less efficient structuring, the raw horsepower of the platforms used made for a much faster server. It is unfortunate that this file server program did not support all of the functionality of the native DNIX server. Tricky things, like named pipes, never worked at all. This was another justification for the named pipe handler process.)
gdb watchpoint support using the features of ISC's MMU
Memory management unit
A memory management unit , sometimes called paged memory management unit , is a computer hardware component responsible for handling accesses to memory requested by the CPU...
Asynchronous I/O, or non-blocking I/O, is a form of input/output processing that permits other processing to continue before the transmission has finished....
to the filesystem was made real. (Originally it blocked anyway.) Kernel processes (kprocs, or threads) were used to do this.
strace is a debugging utility for Linux and some other Unix-like systems to monitor the system calls used by a program and all the signals it receives, similar to "truss" utility in other Unix systems...
-like program. In addition to some repairs to bugs in the standard Unix ptrace single-stepping mechanism, this required adding a temporary process adoption facility so that the tracer could use the standard single-stepping mechanism on existing processes.
A signal is a limited form of inter-process communication used in Unix, Unix-like, and other POSIX-compliant operating systems. Essentially it is an asynchronous notification sent to a process in order to notify it of an event that occurred. When a signal is sent to a process, the operating system...
mechanism extensions. Primarily for the new STOP and CONT signals, but encompassing the new signal control calls as well. Due to ISC's lack of source code for the adb
ADB
ADB is a three-letter acronym that may refer to the intergovernmental organizations:* The Asian Development Bank, a non-profit financial institution whose aim is to help developing Asian countries...
and sdb debuggers the u-page could not be modified, so the new signals could only be blocked or receive default handling, they could not be caught.
A packet analyzer is a computer program or a piece of computer hardware that can intercept and log traffic passing over a digital network or part of a network...
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
driver so that a single event could satisfy more than one I/O request, and conditionally implementing the hardware filtering in software to support promiscuous mode
Promiscuous mode
In computer networking, promiscuous mode or promisc mode is a mode for a network interface controller that causes the NIC to pass all traffic it receives to the central processing unit rather than just passing frames the NIC is intended to receive...
.
Disk mirroring. This was done in the filesystem and not the device driver, so that slightly (or even completely) different devices could still be mirrored together. Mirroring a small hard disk to the floppy was a popular way to test mirroring as ejecting the floppy was an easy way to induce disk errors.
In computing, an inode is a data structure on a traditional Unix-style file system such as UFS. An inode stores all the information about a regular file, directory, or other file system object, except its data and name....
In computing, a symbolic link is a special type of file that contains a reference to another file or directory in the form of an absolute or relative path and that affects pathname resolution. Symbolic links were already present by 1978 in mini-computer operating systems from DEC and Data...
In computing, the sticky bit is an access-right flag that can be assigned to files and directories on Unix systems.-History:The sticky bit was introduced in the Fifth Edition of Unix in 1974 for use with pure executable files. When set, it instructed the operating system to retain the text segment...
directory extensions to the filesystem. Added /dev/zero, /dev/noise, /dev/stdXXX, and /dev/fd/X devices.
Process group id lists (from SVR4).
#! direct script execution.
Serial port multiplication using ISC's Z-80 based VMEbus
VMEbus
VMEbus is a computer bus standard, originally developed for the Motorola 68000 line of CPUs, but later widely used for many applications and standardized by the IEC as ANSI/IEEE 1014-1987. It is physically based on Eurocard sizes, mechanicals and connectors , but uses its own signalling system,...
communications boards.
Movable swap partition.
Core 'dump' snapshots of running processes. Support for fuser
Fuser (Unix)
fuser is a UNIX command used to show which processes are using a specified file, file system, or unix socket. For example, to check process IDs and users accessing a USB drive: # fuser -m -u /mnt/usb1 /mnt/usb1: 1347c 1348c 1349c...
command.
Process renice function. Associated timesharing reprioritizer program to implement floating priorities.
A way to 'mug' a process, instantly depriving it of all memory resources. Very useful for determining what the current working set
Working set
Peter Denning defines “the working set of information W of a process at time t to be the collection of information referenced by the process during the process time interval ”. Typically the units of information in question are considered to be memory pages...
is, as opposed to what is still available to it but not necessarily being used. This was associated with a GUI utility showing the status of all 1024 pages of a process's memory map. (This being the number of memory pages supported by ISC's MMU.) In use you would 'mug' the target process periodically through its life and then watch to see how much memory was swapped back in. This was useful as ISC's production environment used only a few long-lived processes, controlling their memory utilization and growth was key to maintaining performance.
Features that were never added
When DNIX development at ISC effectively ceased in 1997, a number of planned OS features were left on the table:
Shared objects. There were two dynamically-loaded libraries in existence, an encryptor for DNET and the GUI's imaging library, but the facility was never generalized. ISC's machines were characterized by a general lack of virtual address
Virtual address
In computer technology, a virtual address is an address identifying a virtual, i.e. non-physical, entity.-Description:The term virtual address is most commonly used for an address pointing to virtual memory or, in networking, when referring to a virtual network address...
space, so extensive use of memory-mapped entities would not have been possible.
lightweight processes. The kernel itself already had multiple threads that shared a single MMU context, extending this to user processes should have been straightforward. The API implications would have been the most difficult part of this.
An access control list , with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject...
s. Trivial to implement using an ACL handler mounted over the stock filesystem.
Multiple swap partitions. DNIX already used free space on the selected volume for swapping, it would have been easy to give it a list of volumes to try in turn, potentially with associated space limits to keep it from consuming all free space on a volume before moving on to the next one.
Remote kernel debugging via gdb. All the pieces were there to do it either through the customary serial port or over Ethernet using the kernel's embedded X.25 link software, but they were never assembled.
68030 support. ISC's prototypes were never completed. Two processor piggyback plug-in cards were built, but were never used as more than faster 68020's. They were not reliable, nor were they as fast as they could have been due to having to fit into a 68020 socket. The fast context switching ISC MMU would be left disabled (and left out altogether in proposed production units), and the embedded one of the 68030 was to have been used instead, using a derivative of the DS90-20's MMU code. While the ISC MMU was very efficient and supported instant switching among 32 resident processes, it was very limited in addressability. The 68030 MMU would have allowed for much more than 8 MB of virtual space in a process, which was the limit of the ISC MMU. Though this MMU would be slower, the overall faster speed of the 68030 should have more than made up for it, so that a 68030 machine was expected to be in all ways faster, and support much larger processes.
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