Glossary

Glossary of Multics acronyms and terms. Entries by Tom Van Vleck ([THVV]) unless noted. Please post additions or corrections to alt.os.multics, or mail them to Tom Van Vleck.

validation level

When inner ring procedures are called to work on behalf of an outer ring procedure,the validation level indicates the ring number that should be used for access checking. The validation level is a per-ring variable. The file system uses the validation level when initializing ring brackets and default ACLs for new segments.

For example, if a ring-4 program calls a gate into ring 1, the validation level would typically be set to 4, and the ring-1 program would ensure that operations it performed for the ring-4 program were permitted for ring 4, and it would leave the validation level set to 4 when calling ring 0 to perform file system operations. If the ring-1 program needed to set up a ring-1 database, it would save the validation level, set it to the current ring number, call the file system, and restore the validation level.

vfile_

The Multics DIM that allowed users to access segments with read/write calls instead of virtual memory access.

Video System

[BSG] Supported a character based window system and a real-time input editor much like the Unix ksh command line editor. Followed on the heels of Multics Emacs.

VIP7760

[BSG] Honeywell video terminal. Synchronous device, required a controller. Lacking insert or delete lines or characters, it was not well suited for screen-managed video at less than 9600 baud. Prior to Emacs, video terminals were in general less desirable than good printing terminals for any number of reasons.

VIP7801

[BSG] Honeywell video terminal. Worked asynchronously or synchronously. Complete with insert and delete lines and characters and nicely-chiseled high-resolution characters, this was an excellent Emacs terminal popular in the Multics development community, although its high cost kept it from being used almost anywhere outside Honeywell. Developed by Honeywell in Billerica, MA.

virtual cpu

The system keeps track of "virtual" CPU usage for each user, that is, CPU usage not counting overhead. Interrupt service time is subtracted from a process's "real" CPU usage so that a user program incurs repeatable CPU charges for running the same program, regardless of load. See accounting.

virtual memory

[BSG] As in "The Multics Virtual Memory", a paper by Clingen, Bensoussan, and Daley. A Multics process accesses all the data (it is allowed to) on the system as part of a huge, two-dimensional address space (see segmentation). There is no "file I/O", no buffers, no read-in, no write-out. All the data on the system is "virtual memory", paging being handled completely transparently.

VisiCalc

Microcomputer spreadsheet developed by Multicians Bob Frankston and Dan Bricklin. Not derived from Multics except for the authors' experience. Bricklin wrote a line-oriented desk calculator program, calc, for Multics, and did two versions of APL. Frankston did core usage metering.

[Dan Bricklin] The final version of the original VisiCalc was written on the MULTICS system at MIT which we paid dearly for out of our pockets. We used timesharing at night. Bob would get up at 3 PM when I would get back from school and work until 6 or 7 in the morning. Since MIT took three months to bill, we also had a little float.

VLSI Design software

?

VMM

Virtual Machine Monitor. A virtual machine implementation done by Russ McGee of GE Phoenix and a bunch of AEPs in the early 1970s. Users could run virtual 645s and 635s, and run GECOS and Multics simultaneously on a GE-645 under control of the VMM "Hypervisor." Comparable to early versions of IBM's CP-67. Never a product.

volume backup

The volume dumper dumped by physical volumes, like BOS SAVE, but ran while the system was up. Not possible until after NSS. Programmed by Dave Vinograd.

volume map

[BSG] A data structure with one bit for each allocatable record on a Physical Volume, indicating whether the record is in use or available for allocation. Prior to NSS, there was one volume map for the whole system, which was stored in, and more or less known as, the FSDCT. This data base was wired, as disk pages were allocated at the time pages were written out from main memory, and it had to be touched in a wired environment. In NSS, this data base became per-PV, and grew measurably in size, and could no longer be kept wired: Bernie Greenberg, inspired by Decimal Unit prepaging, made it pageable by making instructions taking page faults on unallocated pages appear to take page faults on the volume map, effectively virtualizing a hardware prepage. Being a paged, segmented data base whose paging-out is not controlled, and suffering the same as any such at crash time, the volume maps had to be reconstructed at crash recovery time, consuming a long time per volume (although this was infinitely better than before NSS, when there was only one FSDCT) by the volume salvager.

[WOS] In the early 1980s, inspired by published work on Amber, John Bongiovanni remedied this by a scheme of incremental maintenance of the volume maps by withdrawing limited "record stocks" against it in a synchronous and safe manner, bounding the potential per-crash loss to that limit. Combined with this, John invented the scavenger, a legendarily complex program that regenerated the correct content of volume maps as the system ran by careful cooperation with concurrent record allocation and deallocation activity, to recover such incremental loss at leisure.

volume pool

RCP concept. A volume pool can allocate volumes, e.g. "system-scratch-tape" might contain 100 tapes, and a mount request for "system-scratch-tape" will withdraw one and assign it to the requesting user.

volume salvager

This program is invoked automatically when volumes are mounted, if they were not shut down correctly. It scans the volume's VTOC, and checks that every disk record on the volume is either free or is part of only one filemap, and rebuilds the volume free map.

VOS

Stratus operating system, influenced by Multics, developed by Multicians.

VPI

Virginia Polytechnic Institute, Blacksburg, VA. Multics customer.

VTOC

Volume Table of Contents. OS/360 volumes had these data structures, and NSS adopted the term for its similar database. By defining the segment catalogue of a disk pack as a fixed-record, fixed-form database, NSS achieved a substantial advance in reliability over previous versions of the file system. Source code: vtoc_man.pl1.

VTOCE

VTOC Entry. Very like an inode in the Unix file system. Contains the activation attributes of a segment (date/time modified, page fault count, etc.) and its file map.

VW

[JWG, HVQ] Multics site: Volkswagen of America (Troy MI). Accepted by VW and installed in space Honeywell found for it for a few months (1981-82), before VW of Germany canceled the deal. They claimed VW was supposed to be an all-IBM site and that VW of America didn't have the authority to make such a deal.