ITS Internals Manual - Revision history

Jnc: /* Terminals and controllers */ Add MC details

2023-12-01T12:00:58Z

‎Terminals and controllers: Add MC details

Larsbrinkhoff: New section for terminals and their controllers.

2023-12-01T08:21:53Z

New section for terminals and their controllers.

Jnc: /* Daemons */ typo

2023-10-17T18:56:06Z

‎Daemons: typo

Larsbrinkhoff: /* Jobs */ Typo.

2023-09-15T09:57:36Z

‎Jobs: Typo.

Larsbrinkhoff: A little background info about jobs.

2023-09-15T09:57:07Z

A little background info about jobs.

Jnc: /* External links */ typo

2023-09-15T00:41:27Z

‎External links: typo

Jnc: /* External links */ +useful tips

2023-09-15T00:40:48Z

‎External links: +useful tips

Larsbrinkhoff at 08:28, 14 September 2023

2023-09-14T08:28:20Z

Larsbrinkhoff: Flesh out some I/O devices.

2023-09-14T08:25:51Z

Flesh out some I/O devices.

Jnc: Add stuff from Talk:Daemon

2023-09-13T15:12:50Z

Add stuff from Talk:Daemon

@@ Line 68: / Line 68: @@
 ** GE Datanet 760 controller with four CRT consoles.
 ** A few ARDS terminals.
 * The AI KA10:
 ** TK10 &mdash; 16 low-speed lines.
 ** Systems Concepts DK-10: 16 medium-speed lines with DMA.
 ** Datapoint 3300 CRT terminals.
 * The DM KA10:
 ** "Morton box" controller with 32 very high-speed lines.
-** Imlac PDS-1 "intelligent terminals", or actually full minicomputers.
+** [[Imlac PDS-1]] "intelligent terminals", or actually full [[minicomputer]]s.
 * The ML KA10:
 ** "Morton box".
 ** One Imlac PDS-1.
 * The MC KL10:
-** (Various, to do.)
+** Many lines attached to two [[DH11 asynchronous serial line interface|DH11]]'s and one [[DL11 asynchronous serial line interface|DL11]] (main console [[DECwriter II|LA36]]) on the main [[front end]] [[PDP-11/40]] attached to the [[DTE20 Ten-Eleven Interface|DTE20]].
 ** One Imlac PDS-4.
 * All KS10:
-** DZ11 controller.
+** [[DZ11 asynchronous serial line interface|DZ11]] controller.
 ==Disk controllers==

@@ Line 61: / Line 61: @@
 * Logo TV
 * Imlac PDS-1
 ==Disk controllers==

@@ Line 39: / Line 39: @@
 On ITS, a "dragon" is a permanent system job, and a "demon" is a temporary system job which is started on demand; this terminology is somewhat different (in both in the distinguishing characteristics, as well as in the actual words used) from the classic [[daemon]] terminology. ITS also has both classic daemons (which are ordinary processes, which load their code from the [[file system]], run in the same CPU mode as normal user processes - and thus have a private [[address space]]), and what we are calling 'system processes' [temporary placeholder - I need to send that email to COFF] (whose code is statically linked in with the kernel, and thus loaded into [[main memory]] at [[bootstrapping]] time, and run in 'executive' mode, and thus share the kernel's address space).
-On startup, ITS starts a job called SYSJOB (would this be considered a 'dragon' in ITS terminology?), which does some system tasks (complete list [https://github.com/PDP-10/its/blob/master/doc/sysdoc/usr.102#L664 here]) as a regular job; it is something of a 'system process' as its code is part of the kernel - but it appears to run in user mode (there some confusion over this; see [https://github.com/PDP-10/its/blob/master/doc/sysdoc/usr.102#L664 here]). It runs in usermode, in part, because ITS does not allow jobs to do [[system call]]s from exec mode.
+On startup, ITS starts a job called SYSJOB (would this be considered a 'dragon' in ITS terminology?), which does some system tasks (complete list [https://github.com/PDP-10/its/blob/master/doc/sysdoc/usr.102#L664 here]) as a regular job; it is something of a 'system process' as its code is part of the kernel - but it appears to run in user mode (there some confusion over this; see [https://github.com/PDP-10/its/blob/master/doc/sysdoc/usr.102#L664 here]). It runs in user mode, in part, because ITS does not allow jobs to do [[system call]]s from exec mode.
 There is also a system process called the CORE JOB, which before paging used to shuffle processes around in core, but which now allocates main memory to jobs that need it, and also takes care of user variable blocks, which have to be allocated consecutively, by shuffling those around.

@@ Line 29: / Line 29: @@
 ITS terminology for what is know generally known as a [[process]] is ''job''.  A 'child process' is an ''inferior job'' and the parent is the ''superior''.  The top-level job, HACTRN, can normally handle eight inferiors, though this isn't a hard limit.
-A job has a address space, consisting of 256 pages of 1024 words each.  Each page may individually be mapped to some backing store, and have access read/write bits set.  Backing store is normally anonymous core memory or files, but it can also be PDP-6 or PDP-11 memory.
+A job has an address space, consisting of 256 pages of 1024 words each.  Each page may individually be mapped to some backing store, and have access read/write bits set.  Backing store is normally anonymous core memory or files, but it can also be PDP-6 or PDP-11 memory.
 Jobs can be created by the system itself, see ''How system jobs get started'', or by a user application opening a file on the USR: device which creates an inferior.  The superior can read and write the inferior core image with normal .IOT read/write calls, and there is a ''LOAD'' system call to specify an on-disk file core image to load.

@@ Line 24: / Line 24: @@
 * Bootstrapping
 * Networking
 ==Daemons==

@@ Line 107: / Line 107: @@
 ** [https://github.com/PDP-10/its-vault/blob/master/files/sysdoc/its.histry SYSDOC; ITS HISTRY] - log of changes from ITS 946 to 1263
 ** [https://github.com/PDP-10/its/tree/master/doc/_info_/disk.info DISK INFO] - explanation of the volume hierarchy
-** [https://github.com/PDP-10/its/blob/master/doc/info/tips.2 TIPS > - useful tips
+** [https://github.com/PDP-10/its/blob/master/doc/info/tips.2 TIPS] - useful tips
 ** [https://github.com/PDP-10/its-vault/blob/master/files/%25sys/1412.doc The DMS Batch System]
 * [https://dspace.mit.edu/handle/1721.1/6194 ITS Status Report] - these cover very old versions of the system

@@ Line 37: / Line 37: @@
 Other daemons include COMSAT (the mailer daemon); NAMDRG, which maintains the list of logged in users which appears on all free Knight TV consoles, and PFTHMG DRAGON, which maintains usage (time logged on, and CPU use) statistics. At least one ITS machine, DM, had a 'batch' daemon.
-===Graphical displays===
+===How system jobs get started===
 * Type 340 point-plotting display
@@ Line 46: / Line 54: @@
 * Imlac PDS-1
-===Disk controllers===
+==Disk controllers==
 * Analex
@@ Line 56: / Line 64: @@
 * RH10
 * RH11
 ==The horrible hack hack==

@@ Line 17: / Line 17: @@
 ** Terminals
 *** Terminal-type independent output
 ** Virtual devices
 * Daemons
 * Bootstrapping
@@ Line 33: / Line 36: @@
 Other daemons include COMSAT (the mailer daemon); NAMDRG, which maintains the list of logged in users which appears on all free Knight TV consoles, and PFTHMG DRAGON, which maintains usage (time logged on, and CPU use) statistics. At least one ITS machine, DM, had a 'batch' daemon.
 ===How system jobs get started===

@@ Line 6: / Line 6: @@
 * Jobs
-** User variables
+** User variables/user blocks
 ** Interrupts
 ** How they get started
-* Memory management (pages)
+* Memory management
 * File system
 * I/O
 ** Terminals
@@ Line 21: / Line 24: @@
 ==Daemons==
-ITS has both classic [[daemon]]s (which are ordinary processes, which load their code from the [[file system]], run in the same CPU mode as normal user processes - and thus have a private [[address space]]), and what we are calling 'system processes [temporary placeholder - I need to send that email to COFF] (whose code is statically linked in with the kernel, and thus loaded into [[main memory]] at [[bootstrapping]] time, and run in 'executive' mode, and thus share the kernel's address space).
+[[Image:KnightTV.png|thumb|right|400px|PEEK output, showing 4 system jobs]]
-On startup, ITS starts a job called SYSJOB which does some system tasks as a regular job.  One of the things it does when it starts, is to run SYS; ATSIGN DRAGON which is a central daemon. (On ITS, a "dragon" is a permanent system job, and a "demon" is a temporary system job which is started on demand.) This dragon is also called TARAKA and lives in the CHANNA directory (names taken from the book Lord of Light.)  TARAKA is responsible for starting other dragons in there, which start with the file name RAKASH.  One of those is RAKASH CNAVRL which launches COMSAT (the mailer daemon).
+On ITS, a "dragon" is a permanent system job, and a "demon" is a temporary system job which is started on demand; this terminology is somewhat different (in both in the distinguishing characteristics, as well as in the actual words used) from the classic [[daemon]] terminology. ITS also has both classic daemons (which are ordinary processes, which load their code from the [[file system]], run in the same CPU mode as normal user processes - and thus have a private [[address space]]), and what we are calling 'system processes' [temporary placeholder - I need to send that email to COFF] (whose code is statically linked in with the kernel, and thus loaded into [[main memory]] at [[bootstrapping]] time, and run in 'executive' mode, and thus share the kernel's address space).
-There is also a system process called the CORE JOB, which before paging used to shuffle processes around in core, but which now ??
+On startup, ITS starts a job called SYSJOB (would this be considered a 'dragon' in ITS terminology?), which does some system tasks (complete list [https://github.com/PDP-10/its/blob/master/doc/sysdoc/usr.102#L664 here]) as a regular job; it is something of a 'system process' as its code is part of the kernel - but it appears to run in user mode (there some confusion over this; see [https://github.com/PDP-10/its/blob/master/doc/sysdoc/usr.102#L664 here]). It runs in usermode, in part, because ITS does not allow jobs to do [[system call]]s from exec mode.
-At least one ITS machine, DM, had a 'batch' daemon.
+There is also a system process called the CORE JOB, which before paging used to shuffle processes around in core, but which now allocates main memory to jobs that need it, and also takes care of user variable blocks, which have to be allocated consecutively, by shuffling those around.
-==How system jobs get started==
+Other daemons include COMSAT (the mailer daemon); NAMDRG, which maintains the list of logged in users which appears on all free Knight TV consoles, and PFTHMG DRAGON, which maintains usage (time logged on, and CPU use) statistics. At least one ITS machine, DM, had a 'batch' daemon.
-When ITS wants to start a system job, it calls NUJBST with the SIXBIT job name in T.  The core image in SYS: ATSIGN ''T'' will be started.  This is used to start HACTRN, the Arpanet NETRFC handler, the TCP handler, the CHAOS agent, and demons.
+===How system jobs get started===
 T is stored in a ring buffer, and is read out on a "slow clock" tick by USTART.  A new  job is created, and its user PC is set to 1.  The job accumulators are loaded with code from NUSTCD, which opens the file, calls LOAD, and jumps to the starting address.  In ancient times, the NUSTCD code would first try the file on the SYS: device, and then fall back to the UT2: device; this is a remnant from when ITS ran off DECtape with the system tape mounted on unit 2.