Editing Enterprise (computer) (section)

== Hardware ==
[[File:Enterprise128 02.jpg|thumb|Enterprise 128 rear view]]
[[File:Enterprise128 03.jpg|thumb|Enterprise 128 right view]]

=== CPU, memory and ASIC chips ===

The Enterprise has a 4 [[megahertz]] (MHz) Z80 [[Central processing unit]] (CPU),<ref>{{cite journal |last=Mace |first=Scott |date=6 February 1984 |title=British firm unveils micros at Consumer Electronics Show |url=https://books.google.com/books?id=gC4EAAAAMBAJ&pg=PA3 |journal=[[InfoWorld]] |volume=6 |issue=6 |page=62 |issn=0199-6649 |quote=The Enterprise's Z80 runs at a speed of 4 MHz, [...]}}</ref> 64 KB (65,536 bytes) or 128 KB of RAM, and 32 KB (32,768 bytes) of internal [[read-only memory]] (ROM) that contains the EXOS operating system and a screen editor / word processor. The [[BASIC programming language]] was supplied on a 16 KB ROM module.

Two [[application-specific integrated circuit]] (ASIC) chips take some of the workload off of the central processor. They are named "Nick" and "Dave" after their designers, [[Nick Toop]], who had previously worked on the [[Acorn Atom]], and [[Dave Woodfield]]. "Nick" manages graphics, while "Dave" handles sound and memory paging (bank switching).<ref name="ElanStory" />

A [[bank switching]] scheme allows the memory to be expanded to a maximum of 4 megabytes (4,194,304 bytes). The highest 2 [[address line]]s from the Z80 are used to select one of the four 8-bit Page Registers in the Dave chip. The output from the selected register is used as the highest 8 bits of the 22-bit address bus, while the lowest 14 bits come directly from the Z80 address bus.<ref>{{cite book | title=Enterprise Technical Information | year=1984 | publisher=Enterprise Computers Ltd.}}</ref> Effectively, the 64 KB address space of the Z80 processor is divided into four 16k sections. Any 16k page from the 4 MB address space can be mapped to any of these sections. The lowest two pages (pages 0 and 1) of the 4 MB address space contain system ROM. The next four pages (2 to 5) are reserved for a ROM cartridge (max 64 KB). The top four pages (pages 252 to 255, totaling 64 KB) are used as video RAM, but can be used for storage of program code and data as well. On the 128k model, the additional 64 KB of ram is mapped on pages 248 to 251. The remaining memory space can be used by external devices and memory modules connected to the expansion bus.

=== Keyboard and case ===

The case is unusual in that it contains both a full-sized keyboard with programmable [[function keys]], and a [[joystick]]. Its distinctive shape was due to the designers' desire to break away from customary designs.<ref name="YC_Feb_1985">{{cite journal |date=February 1985 |title=Enterprise Review |url=https://archive.org/details/your-computer-magazine-1985-02/page/n45/mode/2up |journal=[[Your Computer (British magazine)|Your Computer]] |volume=5 |issue=2 |pages=46–48}}</ref> The low-profile keyboard is constructed with mechanical keycaps on top of a rubber membrane and has a standard layout, but the feel of the keys was disliked by many, or even most people, because the keys weren't "full travel", but had a squishy feel, similar to a [[Sinclair QL]] or [[ZX Spectrum#ZX Spectrum+|Spectrum+]]. The joystick replaces the normal cursor keys, and allows the cursor to be moved diagonally.

[[Royal College of Art]] graduates Geoff Hollington and Nick Oakley were responsible for the design, having tendered for this particular contract, and had only seven days to produce the visual design concept. Tooling for production of the casing was also demanded in a rapid timeframe and took five months. Originally, a combination of greys was envisaged for the casing elements, but seeking to avoid the look of office equipment and to appeal to "the lower end of the market", the eventual dark grey case with red, green and blue keys was chosen.<ref name="design198311_enterprise">{{ cite magazine | url=https://archive.org/details/sim_design_1983-11_419/page/n63/mode/2up | title=Enterprise out of the ordinary | magazine=Design | date=November 1983 | access-date=16 March 2022 | last1=Robinson | first1=Colin | pages=62–63 }}</ref>

=== Graphics ===

Enterprise has four hardware graphics modes: 40-column text modes, Lo-Res and Hi-Res [[raster graphics|bit mapped]] graphics, and attribute graphics. The OS offers 80-column text via high-resolution graphics mode. Bit mapped graphics modes allow selection between displays of 2, 4, 16 or 256 colours (from a [[List of monochrome and RGB color formats#3-3-2 bit RGB or 8-8-4 levels RGB|3-3-2 bit RGB palette]]), but horizontal resolution decreases as colour depth increases. [[Interlacing (bitmaps)|Interlaced]] and non-interlaced modes are available. The maximum resolution is {{Resx|640|512}} [[pixels]] interlaced, or {{Resx|640|256}} pixels non-interlaced. These resolutions permit only a 2-colour display. A 256-colour display has a maximum resolution of {{Resx|80|256}}. The attribute graphics mode provides a {{Resx|320|256}} pixel resolution with 16 colours, selectable from a palette of 256.

Multiple pages can be displayed simultaneously on the screen, even if their graphics modes are different. Each page has its own palette, which allows more colours to be displayed onscreen simultaneously. The page height can be larger than the screen or the window it is displayed on. Each page is connected to a channel of the EXOS operating system, so it is possible to write on a hidden page.

=== Sound ===

The sound is handled by the second [[ASIC]] chip, "Dave", and has 3 sound channels plus a noise channel. Each channel's sound can be placed freely in the stereo image. Available effects include [[distortion (music)|distortion]], [[Low-pass filter|low-pass]] and [[high-pass filter]]s, and [[ring modulation]].

The Enterprise [[firmware]] also provides programmable [[envelope (music)|envelope]] generators that are more flexible than synthesizers' traditional [[ADSR envelope]], and allow up to 255 phases to be specified for each envelope. On each phase, the envelope can adjust the sound's [[pitch (music)|pitch]] and [[Panning (audio)|stereo balance]].

=== Interfaces ===

The Enterprise included an array of connectors far beyond what was common on home computers of the time. There is an [[RGB]] output, a [[RS-232]] / [[RS-423]] serial port, a [[Centronics]] printer port, two external joystick ports, two [[cassette tape interface]]s, a [[ROM cartridge]] slot, and an ordinary expansion port. To save expense, many of the connectors did not use sockets, but instead had simple [[edge connector]]s that used the exposed traces at the edge of the [[printed circuit board]].

The BASIC ROM can be replaced by a ROM that emulates a ZX Spectrum 48K, which allows the Enterprise to run the catalogue of thousands of Spectrum BASIC games and any other titles that don't access hardware directly; a hardware peripheral was available to provide more complete emulation for other Spectrum titles — catching Spectrum hardware accesses and issuing an interrupt so that emulation software can deal with them.

An external [[floppy drive]] became available later, and allowed access to [[CP/M]] programs, while at the same time being compatible with the [[MS-DOS]] disc format and [[FAT12]] file structure (sub-directories etc.).