Interface Message Processor - Revision history

Jnc: /* External links */ Bitsavers file rename

2026-10-09T20:53:17Z

External links: Bitsavers file rename

← Older revision		Revision as of 20:53, 9 October 2026
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	==External links==		==External links==

	* [http://www.bitsavers.org/pdf/bbn/imp/~~BBN1763_IMP_InitialDesign_Jan69~~.pdf Initial Design for Interface Message Processors for the ARPA Computer Network]		* [http://www.bitsavers.org/pdf/bbn/imp/BBN-1763_IMP_InitialDesign_Jan69.pdf Initial Design for Interface Message Processors for the ARPA Computer Network]
	* [http://walden-family.com/impcode/ Resurrection of the 1973 IMP code] - While focused on the retrieval, and running under a simulator, of the original IMP code, this site contains much other IMP-related material too (manuals, etc)		* [http://walden-family.com/impcode/ Resurrection of the 1973 IMP code] - While focused on the retrieval, and running under a simulator, of the original IMP code, this site contains much other IMP-related material too (manuals, etc)
	** F.E. Heart, R.E. Kahn, S.M. Ornstein, W.R. Crowther, and D.C. Walden, [http://www.walden-family.com/public/1970-imp-afips.pdf The interface message processor for the ARPA computer network], Proceedings [[American Federation of Information Processing Societies\|AFIPS]], 1970 SJCC, Vol. 36, pp. 551-567.		** F.E. Heart, R.E. Kahn, S.M. Ornstein, W.R. Crowther, and D.C. Walden, [http://www.walden-family.com/public/1970-imp-afips.pdf The interface message processor for the ARPA computer network], Proceedings [[American Federation of Information Processing Societies\|AFIPS]], 1970 SJCC, Vol. 36, pp. 551-567.

Jnc: /* External links */ Link AFIPS

2025-10-06T10:15:49Z

External links: Link AFIPS

← Older revision		Revision as of 10:15, 6 October 2025
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	* [http://www.bitsavers.org/pdf/bbn/imp/BBN1763_IMP_InitialDesign_Jan69.pdf Initial Design for Interface Message Processors for the ARPA Computer Network]		* [http://www.bitsavers.org/pdf/bbn/imp/BBN1763_IMP_InitialDesign_Jan69.pdf Initial Design for Interface Message Processors for the ARPA Computer Network]
	* [http://walden-family.com/impcode/ Resurrection of the 1973 IMP code] - While focused on the retrieval, and running under a simulator, of the original IMP code, this site contains much other IMP-related material too (manuals, etc)		* [http://walden-family.com/impcode/ Resurrection of the 1973 IMP code] - While focused on the retrieval, and running under a simulator, of the original IMP code, this site contains much other IMP-related material too (manuals, etc)
	** F.E. Heart, R.E. Kahn, S.M. Ornstein, W.R. Crowther, and D.C. Walden, [http://www.walden-family.com/public/1970-imp-afips.pdf The interface message processor for the ARPA computer network], Proceedings AFIPS, 1970 SJCC, Vol. 36, pp. 551-567.		** F.E. Heart, R.E. Kahn, S.M. Ornstein, W.R. Crowther, and D.C. Walden, [http://www.walden-family.com/public/1970-imp-afips.pdf The interface message processor for the ARPA computer network], Proceedings [[American Federation of Information Processing Societies\|AFIPS]], 1970 SJCC, Vol. 36, pp. 551-567.
	** [https://walden-family.com/impcode/imp-hardware.pdf Intermodem Processor System] - Honeywell manual covering much of the custom IMP hardware		** [https://walden-family.com/impcode/imp-hardware.pdf Intermodem Processor System] - Honeywell manual covering much of the custom IMP hardware
	** [https://walden-family.com/impcode/imp-code.pdf The Arpanet IMP Program: Retrospective and Resurrection]		** [https://walden-family.com/impcode/imp-code.pdf The Arpanet IMP Program: Retrospective and Resurrection]

Jnc: Move Pluribus IMP image here

2025-09-29T13:33:33Z

Move Pluribus IMP image here

← Older revision		Revision as of 13:33, 29 September 2025
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	[[Image:516IMP.jpg\|thumb\|right\|~~250px~~\|Honeywell 516 IMP]]		[[Image:516IMP.jpg\|thumb\|right\|350px\|Honeywell 516 IMP]]

	The '''Interface Message Processor''' (or '''IMP''', as they were universally known) was the [[packet switch]] which the [[ARPANET]] was made out of; the IMPs were connected to each other via high-speed dedicated point-point telephone links, connected to the IMPs via a [[modem]]. All ARPANET [[host]]s connected to an IMP; connection of a host to an IMP required a special [[network interface]], an [[IMP interface]], which used the asynchronous bit-serial [[1822 interface]] standard, which was especially created for the ARPANET.		The '''Interface Message Processor''' (or '''IMP''', as they were universally known) was the [[packet switch]] which the [[ARPANET]] was made out of; the IMPs were connected to each other via high-speed dedicated point-point telephone links, connected to the IMPs via a [[modem]]. All ARPANET [[host]]s connected to an IMP; connection of a host to an IMP required a special [[network interface]], an [[IMP interface]], which used the asynchronous bit-serial [[1822 interface]] standard, which was especially created for the ARPANET.

	A message from one Host to another was sent via the source Host's IMP, then routed through some number (possibly zero) intermediate IMPs, then through the destination Host's IMP (possibly the same IMP as the first one, in which case the message never went over a telephone line), on to the destination Host. The [[protocol]] which controlled both the channel between the host and IMP, and inter-host communication, was the [[Host-to-IMP Protocol]].		A message from one Host to another was sent via the source Host's IMP, then routed through some number (possibly zero) intermediate IMPs, then through the destination Host's IMP (possibly the same IMP as the first one, in which case the message never went over a telephone line), on to the destination Host. The [[protocol]] which controlled both the channel between the host and IMP, and inter-host communication, was the [[Host-to-IMP Protocol]].

			[[Image:Wharton-DECsystem-10-pluribus.jpg\|thumb\|left\|300px\|Pluribus IMP]]

	The IMPs were 'ruggedized' [[Honeywell]] [[Series 16\|DDP-516]] [[minicomputer]]s, with added special high-speed modem interfaces, and 1822 host interfaces. Later, other variant minicomputers were also used; the Honeywell [[Series 16\|DDP-316]] (a slower, and presumably cost-reduced, [[program compatible]] version of the 516), the [[Pluribus]], and the [[Bolt, Beranek, and Newman\|BBN]] C/30 (which first had [[microcode]] which emulated the Honeywell machines; later an updated "native mode" microcode exposing the full 20-bit hardware).		The IMPs were 'ruggedized' [[Honeywell]] [[Series 16\|DDP-516]] [[minicomputer]]s, with added special high-speed modem interfaces, and 1822 host interfaces. Later, other variant minicomputers were also used; the Honeywell [[Series 16\|DDP-316]] (a slower, and presumably cost-reduced, [[program compatible]] version of the 516), the [[Pluribus]], and the [[Bolt, Beranek, and Newman\|BBN]] C/30 (which first had [[microcode]] which emulated the Honeywell machines; later an updated "native mode" microcode exposing the full 20-bit hardware).

	{{semi-stub}}		{{semi-stub}}

			<br clear=all>

	==External links==		==External links==

Jnc: Link to Series 16 page

2025-09-29T11:13:13Z

Link to Series 16 page

← Older revision		Revision as of 11:13, 29 September 2025
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	A message from one Host to another was sent via the source Host's IMP, then routed through some number (possibly zero) intermediate IMPs, then through the destination Host's IMP (possibly the same IMP as the first one, in which case the message never went over a telephone line), on to the destination Host. The [[protocol]] which controlled both the channel between the host and IMP, and inter-host communication, was the [[Host-to-IMP Protocol]].		A message from one Host to another was sent via the source Host's IMP, then routed through some number (possibly zero) intermediate IMPs, then through the destination Host's IMP (possibly the same IMP as the first one, in which case the message never went over a telephone line), on to the destination Host. The [[protocol]] which controlled both the channel between the host and IMP, and inter-host communication, was the [[Host-to-IMP Protocol]].

	The IMPs were 'ruggedized' [[Honeywell]] DDP-516 [[minicomputer]]s, with added special high-speed modem interfaces, and 1822 host interfaces. Later, other variant minicomputers were also used; the Honeywell DDP-316 (a slower, and presumably cost-reduced, [[program compatible]] version of the 516), the [[Pluribus]], and the [[Bolt, Beranek, and Newman\|BBN]] C/30 (which first had [[microcode]] which emulated the Honeywell machines; later an updated "native mode" microcode exposing the full 20-bit hardware).		The IMPs were 'ruggedized' [[Honeywell]] [[Series 16\|DDP-516]] [[minicomputer]]s, with added special high-speed modem interfaces, and 1822 host interfaces. Later, other variant minicomputers were also used; the Honeywell [[Series 16\|DDP-316]] (a slower, and presumably cost-reduced, [[program compatible]] version of the 516), the [[Pluribus]], and the [[Bolt, Beranek, and Newman\|BBN]] C/30 (which first had [[microcode]] which emulated the Honeywell machines; later an updated "native mode" microcode exposing the full 20-bit hardware).

	{{semi-stub}}		{{semi-stub}}

Jnc: /* External links */ + "'deep dive' analysis of [some of] the IMP code from the early 1970s"

2025-09-13T15:34:03Z

External links: + "'deep dive' analysis of [some of] the IMP code from the early 1970s"

← Older revision		Revision as of 15:34, 13 September 2025
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	** [http://bitsavers.org/pdf/computerControlCompany/series16/h316/70130072180L_DMC_Option_Jun75.pdf H316-20 Data Multiplex Control Option] - DMA controller heavily used by the IMP modem and host interface hardware		** [http://bitsavers.org/pdf/computerControlCompany/series16/h316/70130072180L_DMC_Option_Jun75.pdf H316-20 Data Multiplex Control Option] - DMA controller heavily used by the IMP modem and host interface hardware
	* [http://www.chiappa.net/~jnc/tech/arpanet.html ARPANET Technical Information]		* [http://www.chiappa.net/~jnc/tech/arpanet.html ARPANET Technical Information]
			* [https://elists.isoc.org/pipermail/internet-history/2025-August/010861.html Ruggedized Honeywell 516 ARPANET IMP] - "'deep dive' analysis of [some of] the IMP code from the early 1970s"
			** [https://walden-family.com/impcode/c-listing-ps.txt IMP,3050,IMP] - actual source code listing for the above
	* [https://elists.isoc.org/pipermail/internet-history/2025-August/010815.html The IMP Lights story] - improving the reliability of the IMPs		* [https://elists.isoc.org/pipermail/internet-history/2025-August/010815.html The IMP Lights story] - improving the reliability of the IMPs

	[[Category: ARPANET]]		[[Category: ARPANET]]

Jnc: /* External links */ +The IMP Lights story

2025-09-07T16:30:41Z

External links: +The IMP Lights story

← Older revision		Revision as of 16:30, 7 September 2025
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	** [http://bitsavers.org/pdf/computerControlCompany/series16/h316/70130072180L_DMC_Option_Jun75.pdf H316-20 Data Multiplex Control Option] - DMA controller heavily used by the IMP modem and host interface hardware		** [http://bitsavers.org/pdf/computerControlCompany/series16/h316/70130072180L_DMC_Option_Jun75.pdf H316-20 Data Multiplex Control Option] - DMA controller heavily used by the IMP modem and host interface hardware
	* [http://www.chiappa.net/~jnc/tech/arpanet.html ARPANET Technical Information]		* [http://www.chiappa.net/~jnc/tech/arpanet.html ARPANET Technical Information]
			* [https://elists.isoc.org/pipermail/internet-history/2025-August/010815.html The IMP Lights story] - improving the reliability of the IMPs

	[[Category: ARPANET]]		[[Category: ARPANET]]

Jnc: The DDP-516 came in non-ruggedized form too

2025-01-21T05:55:00Z

The DDP-516 came in non-ruggedized form too

← Older revision		Revision as of 05:55, 21 January 2025
Line 5:		Line 5:
	A message from one Host to another was sent via the source Host's IMP, then routed through some number (possibly zero) intermediate IMPs, then through the destination Host's IMP (possibly the same IMP as the first one, in which case the message never went over a telephone line), on to the destination Host. The [[protocol]] which controlled both the channel between the host and IMP, and inter-host communication, was the [[Host-to-IMP Protocol]].		A message from one Host to another was sent via the source Host's IMP, then routed through some number (possibly zero) intermediate IMPs, then through the destination Host's IMP (possibly the same IMP as the first one, in which case the message never went over a telephone line), on to the destination Host. The [[protocol]] which controlled both the channel between the host and IMP, and inter-host communication, was the [[Host-to-IMP Protocol]].

	The IMPs were [[Honeywell]] DDP-516 ~~'ruggedized'~~ [[minicomputer]]s, with added special high-speed modem interfaces, and 1822 host interfaces. Later, other variant minicomputers were also used; the Honeywell DDP-316 (~~the non~~-~~ruggedized~~ version of the 516), the [[Pluribus]], and the [[BBN]] C/30 (which first had [[microcode]] which emulated the Honeywell machines; later an updated "native mode" microcode exposing the full 20-bit hardware).		The IMPs were 'ruggedized' [[Honeywell]] DDP-516 [[minicomputer]]s, with added special high-speed modem interfaces, and 1822 host interfaces. Later, other variant minicomputers were also used; the Honeywell DDP-316 (a slower, and presumably cost-reduced, [[program compatible]] version of the 516), the [[Pluribus]], and the [[Bolt, Beranek, and Newman\|BBN]] C/30 (which first had [[microcode]] which emulated the Honeywell machines; later an updated "native mode" microcode exposing the full 20-bit hardware).

	{{semi-stub}}		{{semi-stub}}

Jnc: Add image of a 516 IMP

2025-01-15T12:55:51Z

Add image of a 516 IMP

← Older revision		Revision as of 12:55, 15 January 2025
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			[[Image:516IMP.jpg\|thumb\|right\|250px\|Honeywell 516 IMP]]

	The '''Interface Message Processor''' (or '''IMP''', as they were universally known) was the [[packet switch]] which the [[ARPANET]] was made out of; the IMPs were connected to each other via high-speed dedicated point-point telephone links, connected to the IMPs via a [[modem]]. All ARPANET [[host]]s connected to an IMP; connection of a host to an IMP required a special [[network interface]], an [[IMP interface]], which used the asynchronous bit-serial [[1822 interface]] standard, which was especially created for the ARPANET.		The '''Interface Message Processor''' (or '''IMP''', as they were universally known) was the [[packet switch]] which the [[ARPANET]] was made out of; the IMPs were connected to each other via high-speed dedicated point-point telephone links, connected to the IMPs via a [[modem]]. All ARPANET [[host]]s connected to an IMP; connection of a host to an IMP required a special [[network interface]], an [[IMP interface]], which used the asynchronous bit-serial [[1822 interface]] standard, which was especially created for the ARPANET.

Jnc: +links

2024-12-16T02:57:18Z

+links

← Older revision		Revision as of 02:57, 16 December 2024
Line 3:		Line 3:
	A message from one Host to another was sent via the source Host's IMP, then routed through some number (possibly zero) intermediate IMPs, then through the destination Host's IMP (possibly the same IMP as the first one, in which case the message never went over a telephone line), on to the destination Host. The [[protocol]] which controlled both the channel between the host and IMP, and inter-host communication, was the [[Host-to-IMP Protocol]].		A message from one Host to another was sent via the source Host's IMP, then routed through some number (possibly zero) intermediate IMPs, then through the destination Host's IMP (possibly the same IMP as the first one, in which case the message never went over a telephone line), on to the destination Host. The [[protocol]] which controlled both the channel between the host and IMP, and inter-host communication, was the [[Host-to-IMP Protocol]].

	The IMPs were Honeywell DDP-516 'ruggedized' [[minicomputer]]s, with added special high-speed modem interfaces, and 1822 host interfaces. Later, other variant minicomputers were also used; the Honeywell DDP-316 (the non-ruggedized version of the 516), the Pluribus, and the [[BBN]] C/30 (which first had [[microcode]] which emulated the Honeywell machines, later an updated "native mode" microcode exposing the full 20-bit hardware).		The IMPs were [[Honeywell]] DDP-516 'ruggedized' [[minicomputer]]s, with added special high-speed modem interfaces, and 1822 host interfaces. Later, other variant minicomputers were also used; the Honeywell DDP-316 (the non-ruggedized version of the 516), the [[Pluribus]], and the [[BBN]] C/30 (which first had [[microcode]] which emulated the Honeywell machines; later an updated "native mode" microcode exposing the full 20-bit hardware).

	{{semi-stub}}		{{semi-stub}}

Jnc: /* External links */ +Initial Design for Interface Message Processors for the ARPA Computer Network

2023-12-17T18:49:53Z

External links: +Initial Design for Interface Message Processors for the ARPA Computer Network

← Older revision		Revision as of 18:49, 17 December 2023
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	==External links==		==External links==

			* [http://www.bitsavers.org/pdf/bbn/imp/BBN1763_IMP_InitialDesign_Jan69.pdf Initial Design for Interface Message Processors for the ARPA Computer Network]
	* [http://walden-family.com/impcode/ Resurrection of the 1973 IMP code] - While focused on the retrieval, and running under a simulator, of the original IMP code, this site contains much other IMP-related material too (manuals, etc)		* [http://walden-family.com/impcode/ Resurrection of the 1973 IMP code] - While focused on the retrieval, and running under a simulator, of the original IMP code, this site contains much other IMP-related material too (manuals, etc)
	** F.E. Heart, R.E. Kahn, S.M. Ornstein, W.R. Crowther, and D.C. Walden, [http://www.walden-family.com/public/1970-imp-afips.pdf The interface message processor for the ARPA computer network], Proceedings AFIPS, 1970 SJCC, Vol. 36, pp. 551-567.		** F.E. Heart, R.E. Kahn, S.M. Ornstein, W.R. Crowther, and D.C. Walden, [http://www.walden-family.com/public/1970-imp-afips.pdf The interface message processor for the ARPA computer network], Proceedings AFIPS, 1970 SJCC, Vol. 36, pp. 551-567.
Line 16:		Line 17:
	** [http://bitsavers.org/pdf/computerControlCompany/series16/h316/70130072156_316_516_PgmrRef_Nov70.pdf Models 316 and 516 Programmers' Reference Manual]		** [http://bitsavers.org/pdf/computerControlCompany/series16/h316/70130072156_316_516_PgmrRef_Nov70.pdf Models 316 and 516 Programmers' Reference Manual]
	** [http://bitsavers.org/pdf/computerControlCompany/series16/h316/70130072180L_DMC_Option_Jun75.pdf H316-20 Data Multiplex Control Option] - DMA controller heavily used by the IMP modem and host interface hardware		** [http://bitsavers.org/pdf/computerControlCompany/series16/h316/70130072180L_DMC_Option_Jun75.pdf H316-20 Data Multiplex Control Option] - DMA controller heavily used by the IMP modem and host interface hardware

	* [http://www.chiappa.net/~jnc/tech/arpanet.html ARPANET Technical Information]		* [http://www.chiappa.net/~jnc/tech/arpanet.html ARPANET Technical Information]

	[[Category: ARPANET]]		[[Category: ARPANET]]