Editing Hercules Graphics Card

{{Short description|IBM PC graphic adapter and display standard}}
{{Infobox GPU
| name = Hercules Graphics Card
| image = KL Hercules HGC.png 
| caption = HGC with parallel port
| codename = 
| created = {{Start date and age|1982}}
| transistors = 
| architecture = [[Motorola 6845]]
| entry = Hercules Graphics Card
| midrange = [[#Hercules_Graphics_Card_Plus|Hercules Graphics Card Plus]]
| highend = [[Hercules InColor Card]]
| predecessor = [[IBM Monochrome Display Adapter|MDA]], [[Color Graphics Adapter|CGA]]
| successor = [[Enhanced Graphics Adapter]]
}}

The '''Hercules Graphics Card''' ('''HGC''') is a computer [[video card|graphics controller]] formerly made by [[Hercules Computer Technology|Hercules Computer Technology, Inc.]] that combines [[IBM]]'s [[Text-based user interface|text-only]] [[IBM Monochrome Display Adapter|MDA]] display standard with a [[Raster graphics|bitmapped graphics]] mode, also offering a [[Parallel port|parallel printer port]].<ref name=":2" /><ref>{{Cite web |title=Hardware / Hercules Computer Technology, HTC // retrocmp / retro computing |url=https://retrocmp.de/hardware/hercules-card/hercules-card.htm#hgc |access-date=2023-04-13 |website=retrocmp.de}}</ref> This allows the HGC to offer both high-quality text and graphics from a single card.

The HGC was very popular and became a widely supported [[De facto standard|de facto]] [[computer display standard|display standard]] on [[IBM PC compatible]]s. The HGC standard was used long after more technically capable systems had entered the market, especially on [[dual-monitor]] setups.

==History==
The Hercules Graphics Card was released to fill a gap in the IBM video product lineup. When the [[IBM Personal Computer]] was launched in 1981, it had two graphics cards available: the [[Color Graphics Adapter]] (CGA) and the [[Monochrome Display Adapter|Monochrome Display And Printer Adapter]] (MDA). CGA offered low-resolution ({{resx|320x200}}) color graphics and medium-resolution ({{resx|640x200}}) monochrome graphics, while MDA offers a sharper text mode (equivalent to {{resx|720×350}}) but has no per-pixel addressing modes and is limited to a fixed [[Character encoding|character set]].

These adapters were quickly found to be inadequate by the market, creating a demand for a card that offers high-resolution graphics and text.<ref>{{Cite news |last=Gibson |first=Steve |date=19 Sep 1988 |title=IBM's EGA unified backward-compatible CGA, MDA, Hercules standards |pages=49 |work=InfoWorld |url=https://books.google.com/books?id=mDoEAAAAMBAJ&q=IBM+MDA+more+popular+than+CGA&pg=PA49}}</ref> The founder of [[Hercules Computer Technology]], Van Suwannukul, created the Hercules Graphics Card so that he could work on his [[Thesis|doctoral thesis]] on an [[IBM PC]] using the [[Thai alphabet]], impossible with the low resolution of CGA or the fixed character set of MDA.<ref>{{Cite news |date=16 May 1989 |title=Monitors for VGA and beyond |pages=96 |work=PC Magazine |url=https://books.google.com/books?id=2jkWJsu_9CoC&q=van+suwannukul+hercules&pg=RA1-PA96}}</ref> It initially retailed in 1982 for $499.<ref>{{Cite news |last=Welch |first=Mark |date=1 September 1986 |title=Hercules improves its monochrome card |pages=42 |work=InfoWorld |url=https://books.google.com/books?id=cS8EAAAAMBAJ&dq=hercules+graphics+price&pg=PA42}}</ref>

== Hardware design ==
The original HGC is an [[Industry Standard Architecture|8-bit ISA]] card with 64&nbsp;KB of [[Random-access memory|RAM]], visible on the board as eight 4164 RAM chips, and a [[D-subminiature|DE-9 output]] compatible with the [[IBM 5151|IBM monochrome monitor]] used with the MDA. Like the MDA, it includes a parallel interface for attaching a printer.<ref name=":2">{{Cite news |date=27 September 1982 |title=Hardware News |pages=77 |work=InfoWorld |url=https://books.google.com/books?id=BzAEAAAAMBAJ&q=infoworld+1982+hercules&pg=PA77}}</ref>

The video output is 5&nbsp;V [[Transistor–transistor logic|TTL]], as with the MDA card.<ref name="nemesis">{{cite web |title=IBM PC-Compatible EGA Video Reference |url=http://nemesis.lonestar.org/reference/video/ega.html |access-date=2007-08-22 |archive-url=https://web.archive.org/web/20140511072035/http://nemesis.lonestar.org/reference/video/ega.html |archive-date=2014-05-11 |url-status=dead}} 070822 nemesis.lonestar.org</ref><ref name="ports">{{Cite web |last=White |first=Ray |date=2004 |title=Monitor Ports - Obsolete Interfaces |url=https://whitefiles.org/b1_s/1_free_guides/fg1mt/pgs/h10f.htm |website=Technology Guides|archive-url=https://web.archive.org/web/20170322001323/https://whitefiles.org/b1_s/1_free_guides/fg1mt/pgs/h10f.htm |archive-date=2017-03-22 }}</ref><ref>{{Cite web |date=2011 |title=PC video hardware page: Monitor connections |url=http://www.epanorama.net/links/pc_video.html#monitor |access-date=2023-04-13 |website=ePanorama.net|archive-url=https://web.archive.org/web/20170317051011/http://www.epanorama.net/links/pc_video.html#monitor |archive-date=2017-03-17 }}</ref> Nominally, the Hercules card provides a horizontal scanning frequency of 18.425&nbsp;±&nbsp;0.500&nbsp;kHz and 50&nbsp;Hz vertical.<ref name="industrial-monitors">{{cite web |title=Industrial monochrome monitors 7"–14" |url=http://www.adm-electronic.de/pdf/MNL115_ita_eng.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070202201848/http://www.adm-electronic.de/pdf/MNL115_ita_eng.pdf |archive-date=2007-02-02}} 070822 adm-electronic.de</ref> It runs at two slightly different sets of frequencies depending on whether in text or graphics mode, providing a different vertical refresh rate and a different aspect ratio via a different pixel clock and number of scanlines.{{Citation needed|date=August 2020}}

== Capabilities ==
[[File:Hercules Graphics Card test image.png|thumb|Wikipedia logo rendered at {{resx|720x348}} without aspect ratio correction]]
[[File:Wikipedia logo on Hercules display (adjusted).png|thumb|Wikipedia logo displayed on a CRT monitor by a Hercules-compatible video card]]
[[File:Hercules graphics simulated image.png|thumb|Hercules image at {{resx|720x348}} without aspect ratio correction]]
[[File:Hercules graphics (aspect ratio corrected).png|thumb|Hercules image with correct aspect ratio as would be seen on a [[Fullscreen (aspect ratio)|4:3 monitor]]]]
The Hercules card provides two modes: 
* {{resx|80×25}} [[text mode]] with {{resx|9×14}} pixel font (effective resolution of {{resx|720×350}}, MDA-compatible)
* {{resx|720×348}} graphics mode (pixel-addressable graphics)<ref name=":0">{{Cite news |last=Pointing |first=Bob |date=June 26, 1989 |title=High-Resolution Standard Is Latest Step in DOS Graphics Evolution |pages=48 |work=InfoWorld |url=https://books.google.com/books?id=lTAEAAAAMBAJ&q=infoworld+1982+hercules&pg=PT47}}</ref>

The text mode of the Hercules card uses the same signal timing as the MDA text mode.

The Hercules graphics mode is similar to the CGA high-resolution ({{resx|640×200}}) two-color mode; the [[Framebuffer|video buffer]] contains a packed-pixel bitmap (eight pixels per byte, one bit per pixel) with the same byte format—including the pixel-to-bit mapping and byte order—as the CGA two-color graphics mode, and the video buffer is also split into interleaved banks, each 8&nbsp;KB in size.

However, because in the Hercules graphics mode there are more than 256 scanlines and the display buffer size is nearly 32&nbsp;KB (instead of 16&nbsp;KB as in all CGA graphics modes), four interleaved banks are used in the Hercules mode instead of two as in the CGA modes. Also, to represent 720 pixels per line instead of 640 as on the CGA, each scanline has 90 bytes of pixel data instead of 80.<ref name="manual101">{{cite book |title=Hercules Graphics Card Owner's Manual |page=16}}</ref>

The 64&nbsp;KB RAM of the HGC can hold two graphics display pages.  Either page can be selected for display by setting a single bit in the Mode Control Register.  Another bit, in a configuration register exclusive to the HGC, determines whether the second&nbsp;32 KB of RAM on the HGC is accessible to the CPU at the base address B8000h.  This bit is reset at system reset (e.g. power-on) so that the card does not conflict with a CGA or other color card at address B8000h.<ref name="manual101b">{{cite book |title=Hercules Graphics Card Owner's Manual |page=3}}</ref>

== Use ==
In text mode, the HGC appears exactly like an MDA card.<ref name="wadlow198312">{{cite news |url=https://archive.org/stream/byte-magazine-1983-12/1983_12_BYTE_08-12_Easy_Software#page/n343/mode/2up |title=The Hercules Graphics Card |work=BYTE |date=December 1983 |access-date=2013-10-20 |author-last=Wadlow |author-first=Tom |pages=343}}</ref> Graphics mode requires new techniques to use. Unlike the MDA and CGA, the [[BIOS|PC BIOS]] provides no intrinsic support for the HGC. Hercules developed extensions, called ''HBASIC'', for [[IBM BASIC|IBM Advanced BASIC]] to add HGC support<ref>{{Cite news |last=Wadlow |first=Tom |date=December 1983 |title=The Hercules Graphics Card |pages=343 |work=BYTE Magazine |url=https://www.tech-insider.org/personal-computers/research/acrobat/8312.pdf}}</ref> and Hercules cards came with ''Graph X'', a [[software library]] for Hercules graphical-mode support and [[geometric primitive]]s.{{r|wadlow198312}}

Popular IBM PC programs such as [[Lotus 1-2-3]] spreadsheet,{{r|wadlow198312}} [[AutoCAD]] computer-aided drafting, [[Pagemaker]] and [[Xerox Ventura]] desktop publishing, and [[Microsoft Flight Simulator 2.0]] came with their own drivers to use the Hercules graphics mode.<ref>{{Cite web |date=May 1984 |title=Microsoft Flight Simulator (v2.0) back cover scan |url=https://www.mobygames.com/game/pc-booter/microsoft-flight-simulator-v20/cover-art/gameCoverId,2149/ |website=MobyGames}}</ref>

Though the graphics mode of the Hercules card is not CGA-compatible, it is similar enough to the two CGA graphics modes that with the use of third-party [[terminate-and-stay-resident program]]s it can also work with programs written for the CGA card's standard graphics modes. As the Hercules card does not actually have color-generating circuitry, nor can it connect to a color monitor, color appears as simulated grayscale in varying [[Dither|dithering patterns]].<ref>{{Cite web|title=ibm pc - How do CGA emulators for Hercules graphics work?|url=https://retrocomputing.stackexchange.com/questions/6963/how-do-cga-emulators-for-hercules-graphics-work|access-date=2021-02-07|website=Retrocomputing Stack Exchange}}</ref><ref>{{Cite web |title=CGA Simulators for Hercules Cards |url=https://www.dosdays.co.uk/topics/cga_simulators_for_hercules.php |access-date=2022-12-03 |website=DOS Days - Old PC Computing Resource}}</ref><ref>{{Cite web |last=Guzis |first=C. |date=1987 |title=SIMCGA - A CGA SIMULATOR FOR MONOCHROME GRAPHICS CARDS |url=https://www.pcorner.com/list/GRAPHUTI/SIMCGA41.ZIP/INFO/ |access-date=2022-12-03 |website=The Programmer's Corner |archive-date=2022-12-03 |archive-url=https://web.archive.org/web/20221203150326/https://www.pcorner.com/list/GRAPHUTI/SIMCGA41.ZIP/INFO/ |url-status=dead }}</ref>

[[Clone (computing)|Clones]] of the Hercules appeared, including generic models at very low prices, usually without the printer port. Hercules advertisements implied that use of generic Hercules clones can damage the monitor.<ref name="Byte_Magazine">{{cite news |url=https://archive.org/details/byte-magazine-1985-04-rescan/page/n25|title=Hercules ad from Byte Magazine April 1985|work=Byte Magazine|date=April 1985}}</ref>

== Reception ==
The Hercules Graphics Card was very successful, especially after Lotus 1-2-3 supported it, with one-half million units sold by 1985. {{asof|1986|06}} Hercules Computer Technology had 18% of the graphics card market, second to IBM.<ref>{{Cite news |last=Bright |first=David |date=June 23, 1986 |title=Hercules graphics card to debut |pages=52 |work=Computerworld |url=https://books.google.com/books?id=mop2UUCt4kIC&q=computerworld+hercules+1982&pg=PA52}}</ref> Hercules-compatible graphics cards shipped as standard hardware with most [[IBM PC compatible|PC clones]]. As a [[de facto standard]], support in software was widespread.<ref name=":0" />

== Card versions ==
The Hercules Graphics Card had several versions.

=== Hercules Graphics Card ===
Several updated versions of the original '''Hercules Graphics Card''' exist. The original board from 1982 is referenced as '''GB100''', with updated versions in 1983 ('''GB101'''), 1984 ('''GB102''') and 1988 ('''GB102Z''').<ref>{{Cite web |last=Brase |first=Thomas |title=Hardware / Hercules Computer Technology, Hercules Graphics Cards (HGC) |url=https://retrocmp.de/hardware/hercules-card/hercules-card.htm#hgc |access-date=2023-04-13 |website=retrocmp.de - BRING OLD HARDWARE BACK TO LIFE AGAIN}}</ref>

=== Hercules Graphics Card Plus ===
The '''Hercules Graphics Card Plus''' or '''HGC+''' ('''GB112''') was released in June 1986 at an original retail price of $299.<ref name="InfoWorld 1 Sep 19862">{{Cite news |last=Welch |first=Mark |date=September 1, 1986 |title=Hercules improves its monochrome card |pages=41 |work=InfoWorld |url=https://books.google.com/books?id=cS8EAAAAMBAJ&pg=PA41}}</ref> It was an enhancement of the HGC, adding support for redefinable fonts called RAMFONT in [[IBM Monochrome Display Adapter|MDA]]-compatible text mode.<ref name="Elliott_2012_HGCPlus2">{{cite web |author-last=Elliott |author-first=John C. |date=2012-08-09 |title=Hercules Graphics Card Plus: Notes |url=http://www.seasip.info/VintagePC/hercplus.html |url-status=live |archive-url=https://web.archive.org/web/20161123124757/http://www.seasip.info/VintagePC/hercplus.html |archive-date=2016-11-23 |access-date=2016-11-23 |website=John Elliott's homepage}}</ref> It was based around a specialty chip designed by Hercules Computer Technology, unlike the original Hercules Graphics Card, which used standard components.<ref>{{cite journal |date=October 1986 |title=Inside the IBM PC: Before you consider the Hercules Graphics Card Plus consider the technology behind it |url=https://archive.org/stream/198610ByteMagazineVol1111InsideTheIBMPC/198610%20Byte%20Magazine%20Vol%2011-11%20Inside%20the%20IBM%20PC#page/n259/mode/2up/search/RAMfont |journal=[[Byte Magazine]] |type=Advertisement |volume=11 |access-date=2016-11-24}}</ref> Software support included [[Lotus 1-2-3]]&nbsp;v2, [[Lotus Symphony (MS-DOS)|Symphony]]&nbsp;1.1, [[Framework&nbsp;II]] and [[Microsoft Word]]&nbsp;3.<ref name="InfoWorld 1 Sep 19862" />

=== Hercules Network Card Plus ===
In 1988 Hercules released the '''Hercules Network Card Plus''', ('''HNC NB112''') a variant of the Graphics Card Plus with an integrated [[TOPS (file server)|TOPS]]/FlashTalk-compatible network adapter.<ref>{{Cite news |last1=Stephens |last2=Moran |date=March 21, 1988 |title=Hercules to ship card after 3-month delay |page=21 |work=InfoWorld |url=https://books.google.com/books?id=9j4EAAAAMBAJ&q=hercules+network+card&pg=PA21}}</ref> Like the HGC+, it supported RAMFONT, but lacked a printer port.<ref>{{cite journal|author=CW|date=1988-04-22|title=Hercules bringt neues PC-Board mit Ramfont: Grafik und Netzwerk auf einer Karte|url=http://www.computerwoche.de/a/grafik-und-netzwerk-auf-einer-karte,1154889|journal=[[Computerwoche]]|language=de|access-date=2016-11-24}}</ref><ref>{{cite journal|date=1988-05-31|title=Hercules Network Card Plus|url=https://books.google.com/books?id=voPUUGTC56UC&pg=PA262|journal=[[PC Magazine]]|access-date=2016-11-24}}</ref><ref>{{Cite news |last=Patton |first=Carole |date=October 26, 1987 |title=Hercules Weds Networking and Video on 1 Board |pages=20 |work=InfoWorld |url=https://books.google.com/books?id=_z4EAAAAMBAJ&q=hercules+network+card+parallel&pg=PA20}}</ref>

=== Hercules InColor Card ===
{{Main articles|Hercules InColor Card}}
The '''InColor Card''' ('''GB222''') was introduced in April 1987. It included color capabilities similar to the [[Enhanced Graphics Adapter|EGA]], with 16 colors from a palette of 64. It retained the same two modes ({{resx|80×25}} text with redefinable fonts and {{resx|720×348}} graphics), and was backward-compatible with software written for the earlier monochrome Hercules cards.<ref name="Elliot_2012_InColor">{{cite web |author-last=Elliott |author-first=John C. |date=2012-08-05 |title=Hercules InColor Card: Notes |url=http://www.seasip.info/VintagePC/incolor.html |url-status=live |archive-url=https://web.archive.org/web/20161123123816/http://www.seasip.info/VintagePC/incolor.html |archive-date=2016-11-23 |access-date=2016-11-23}} (Pictures and programming information)</ref><ref name="Wilton_1993">{{cite book |author-last=Wilton |author-first=Richard |title=Programmer's guide to the PC & PS/2 video systems |date=1987 |publisher=[[Microsoft Press]] |isbn=1-55615-103-9 |edition=1st}} (NB. The second edition does no longer discuss the InColor and [[Multi-Color Graphics Array|MCGA]] cards at detail level.)</ref><ref name="Brown_2000_RBIL">{{cite web |author-last=Brown |author-first=Ralf D. |author-link=Ralf D. Brown |date=2012-01-21 |title=Public Files on FTP.CS.CMU.EDU - The x86 Interrupt List aka "Ralf Brown's Interrupt List" (RBIL) |url=https://www.cs.cmu.edu/~ralf/files.html |url-status=live |archive-url=https://web.archive.org/web/20160616113421/https://www.cs.cmu.edu/~ralf/files.html |archive-date=2016-06-16 |access-date=2016-06-16 |orig-year=2000-07-16}}</ref><ref name=":02">{{Cite web |last=Brase |first=Thomas |title=Hardware / Hercules Computer Technology, Hercules InColor Card (GB222) |url=https://retrocmp.de/hardware/hercules-card/hercules-card.htm#hicc |access-date=2023-03-01 |website=retrocmp - retro computing}}</ref><ref name=":1">{{Cite news |last=CBR Staff Writer |date=March 1987 |title=PERSONAL GRAPHICS: HERCULES TO BURST INTO 16 COLOURS |work=Tech Monitor |url=https://techmonitor.ai/technology/personal_graphics_hercules_to_burst_into_16_colours}}</ref>

=== Hercules Color Card ===
The '''Hercules Color Card''' ('''GB200''') was a CGA-compatible video board and should not be confused with the InColor Card.<ref>{{Cite book |url=https://minuszerodegrees.net/manuals/Hercules/Hercules%20Color%20Card%20GB200%20-%20Owner's%20Manual%20-%20PARTIAL.pdf |title=Hercules Color Card GB200 - Owner's Manual |publisher=Hercules}}</ref> This board could coexist with the HGC and still allow both graphics pages to be used.<ref>{{Cite web |last=Brase |first=Thomas |title=Hardware / Hercules Computer Technology, Hercules Color Card (GB200) |url=https://retrocmp.de/hardware/hercules-card/hercules-card.htm#hcc |access-date=2023-03-13 |website=retrocmp.de - BRING OLD HARDWARE BACK TO LIFE AGAIN}}</ref> It would detect when the second graphics page was selected and disable access to its own memory, which would otherwise have been at the same addresses. A version without printer port exists<ref>{{Cite web |last=Brase |first=Thomas |title=Hardware / Hercules Computer Technology, Hercules Color Card/NP |url=https://retrocmp.de/hardware/hercules-card/hercules-card.htm#hccnp |access-date=2023-04-13 |website=retrocmp.de}}</ref>

=== Hercules Text Card ===
The '''Hercules Text Card''' was a text-only MDA clone, but offered a parallel printer port.<ref>{{Cite web |last=Brase |first=Thomas |title=Hardware / Hercules Computer Technology, Hercules Text Card |url=https://retrocmp.de/hardware/hercules-card/hercules-card.htm#htc |access-date=2023-04-13 |website=retrocmp.de - BRING OLD HARDWARE BACK TO LIFE AGAIN}}</ref>

== Clone boards ==

Other boards offered Hercules compatibility.<ref name="vgamuseum">{{Cite web |url=http://www.vgamuseum.info/index.php/component/content/article/59-vlasks-articles/index.php?option=com_customproperties&view=show&task=show&cp_made=&cp_bus=&cp_memsize=&cp_year=&cp_memory=&cp_family=&cp_cardtype=hercules&cp_owner=&cp_directx=&cp_opengl=&cp_pipelines=&cp_manufacturer=&cp_process=&cp_text_search= |title=VGA Legacy |access-date=2014-06-28 |archive-url=https://archive.today/20140629122627/http://www.vgamuseum.info/index.php/component/content/article/59-vlasks-articles/index.php?option=com_customproperties&view=show&task=show&cp_made=&cp_bus=&cp_memsize=&cp_year=&cp_memory=&cp_family=&cp_cardtype=hercules&cp_owner=&cp_directx=&cp_opengl=&cp_pipelines=&cp_manufacturer=&cp_process=&cp_text_search= |archive-date=2014-06-29 |url-status=dead}}</ref>

* [[Silicon Integrated Systems|SiS]] 86C12, 86C22
* [[ATI Technologies|ATI]] Small Wonder Graphics Solution, 18700, Graphics Solution Plus
* [[Tamarack Microelectronics]] TD3088A, TD3088A2, TD3088A3, TD3010, RY-3301, TD3010
* [[Yamaha Corporation|Yamaha]] V6366C-F, V6363-F, V6363
* [[Winbond]] W86855AF, W86855AF
* [[NEC]] μPD65042GD
* [[Tseng Labs]] ET1000-A
* [[DFI]] MG-150
* [[Hitachi]] HD6445P4, HD6845SP
* RAM MCG2502, MCG2502
* Proton PT6121T
* [[Acer Inc.|Acer]] M3127
* [[Sigma Designs]] 53C101+53C280A
* CM607P
* [[AST Research]] AST Preview!<ref>{{Cite book |url=https://vintageapple.org/byte/pdf/198509_Byte_Magazine_Vol_10-09_10th_Anniversary_Issue.pdf|title=Byte Magazine September 1985, page 19|year=1985|pages=19}}</ref>

Certain later models of the [[Tandy 1000]] (such as the 1000 TL and SL) and the [[Epson Equity]]<ref name=":9">{{Cite book |url=https://files.support.epson.com/pdf/e1p___/e1p___u1.pdf |title=Equity I+ User's Guide and Diagnostics |publisher=Epson |year=1986 |pages=}}</ref> contained circuitry built into their CPU boards that supported Hercules display modes in addition to their standard CGA modes.

<gallery class="center" widths="160px" heights="120px">
ET1000-A.JPG|[[Tseng Labs|Tseng]] ET-1000 Hercules compatible card
ATI Hercules Card 1986 (cropped and transparent).png|[[ATI Technologies|ATI]] Hercules compatible card from 1986
HGCclone.jpg|A [[Tamarack Microelectronics]] Hercules compatible card
Uncle-RAY.jpg|Uncle-RAY Hercules compatible card
</gallery>

==See also==
{{Commons category|HGC}}
* [[Orchid Graphics Adapter]]
* [[Plantronics Colorplus]]
* [[IBM Monochrome Display Adapter]]
* [[Color Graphics Adapter]]
* [[Light pen]]
* [[List of display interfaces]]
* [[List of defunct graphics chips and card companies]]

== References ==
{{reflist}}

== Further reading ==
{{refbegin}}
* Wilton, Richard (1987) ''Programmer's Guide To PC and PS/2 Video Systems'', Microsoft Press, {{ISBN|1-55615-103-9}}
* Hercules Computer Technology (1987) ''Hercules Compatibility Guide'' (a leaflet)
* [http://wi-fiplanet.webopedia.com/TERM/H/Hercules_graphics.html "Hercules graphics" definition] {{Webarchive|url=https://web.archive.org/web/20050325212616/http://wi-fiplanet.webopedia.com/TERM/H/Hercules_graphics.html |date=2005-03-25 }}, ''Wi-FiPlanet.com''
* [http://support.microsoft.com/kb/51886 How to Print Hercules Graphics SCREEN 3 to an Epson Printer] {{Webarchive|url=https://web.archive.org/web/20090510000628/http://support.microsoft.com/kb/51886 |date=2009-05-10 }}, ''[[Microsoft|Microsoft.com]]''
* [http://everything2.com/index.pl?node_id=1130121 Hercules Monochrome Graphics Adapter], ''[[Everything2.com]]''
{{refend}}

{{Computer display standard}}

[[Category:Graphics cards]]
[[Category:Computer display standards]]
[[Category:Monochrome Display Adapter]]
[[Category:Computer-related introductions in 1982]]