ZX Spectrum+

Introduction

In October 1984, Sinclair Research introduced the ZX Spectrum+, an updated version of the highly successful 48K ZX Spectrum. The new machine replaced the distinctive rubber-key case with a larger, more conventional design and introduced a substantially improved keyboard, while retaining the Spectrum's established hardware architecture and compatibility with its existing software library.

Rumours of a new Spectrum with a conventional keyboard had circulated for some time, but Sinclair Research had repeatedly denied that such a machine was being developed. When the Spectrum+ finally appeared, it brought the familiar electronics of the 48K Spectrum into a new case whose styling followed the design language of the recently introduced QL.

The Spectrum+ was therefore not intended to replace the Spectrum with an entirely new computer. Instead, Sinclair addressed some of the weaknesses of the original design while preserving the large software and hardware ecosystem that had grown around the machine.

The new case

The distinctive wedge-shaped case of the original Spectrum was replaced by a larger, more angular enclosure finished in black ribbed plastic. The new case was approximately 320 mm × 140 mm × 40 mm and was considerably longer than the original machine.

Two folding feet were incorporated underneath the case. When extended, these raised the rear of the keyboard and provided a more conventional typing angle; when folded away, the computer could sit flat on the desk.

A reset button was also fitted to the left-hand side of the case. This was a useful improvement for Spectrum owners, as resetting the computer no longer required the power supply to be disconnected and reconnected. The machine still did not have a conventional mains on/off switch.

Although the new case looked considerably more substantial, Sinclair had not abandoned the basic Spectrum design. The computer remained a 48K Spectrum in terms of its principal capabilities, with the changes concentrated largely on the physical design and keyboard.

The new keyboard

The most obvious improvement was the keyboard. The small moulded rubber keytops of the original Spectrum were replaced by hard plastic keycaps arranged in a much more conventional layout. There were 58 keys in total, including a number of new keys that made frequently used functions easier to enter.

Despite its conventional appearance, the Spectrum+ continued to use the Spectrum's membrane-based keyboard switching system. The flexible membrane remained beneath the keys, while the new moulded keycaps provided a much more substantial typing experience.

A proper space bar and separate cursor controls were provided, while several functions which had previously required combinations involving SHIFT could now be entered directly.

Dedicated keys were provided for CAPS LOCK, DELETE, EDIT, BREAK, TRUE VIDEO, INVERSE VIDEO, GRAPHICS and EXTENDED MODE.

Separate keys were also provided for punctuation such as the comma, full stop, semicolon and inverted comma. Two CAPS SHIFT keys and two SYMBOL SHIFT keys were retained, making frequently used combinations easier to reach.

The new keyboard made programming considerably more convenient, particularly for users who regularly entered graphics and extended-mode commands. It also made the Spectrum more suitable for applications such as word processing, where the original rubber keyboard could be uncomfortable during extended typing.

The keyboard was not universally praised, however. Its compact layout still contained some unusual decisions and the removal of the original colour-coded key legends meant that some of the different Spectrum keyboard modes were less immediately obvious.

The key legends were formed into the moulded keycaps rather than simply being printed onto their surface, helping to prevent them from wearing away through use.

The hardware

The Spectrum+ retained the fundamental hardware architecture of the 48K Spectrum. It used the same Z80A processor running at approximately 3.5 MHz, 48K of RAM and 16K of ROM containing the Spectrum's BASIC and operating routines.

The display system remained the familiar 256 × 192 pixel colour display with the Spectrum's eight basic colours, attribute-based colour control and flashing and brightness features. Sound continued to be produced through the built-in one-bit beeper.

The machine also retained the Spectrum's expansion system and could use the large range of Sinclair and third-party peripherals developed for the original computer.

There were nevertheless differences between the various Spectrum+ circuit board revisions, and the machine represents an important stage in the development of the Spectrum hardware. Later Spectrum designs would introduce further changes to the board layout and integrate more of the logic into fewer components.

Compatibility

One of the most important decisions made with the Spectrum+ was to preserve compatibility with the existing Spectrum software library. The machine remained fundamentally a 48K Spectrum, allowing the huge collection of commercial and user-written programs already available for the computer to continue to be used.

The same principle applied to much of the existing peripheral ecosystem. However, the new case could create practical problems for some accessories which had been designed to plug directly into the original Spectrum's edge connector. The altered shape and position of the case meant that certain peripherals required an extension or modification to fit correctly.

Preserving compatibility was commercially important. By 1984 the Spectrum already had an enormous library of software and a substantial installed user base. Users could therefore buy the new machine without abandoning the programs and accessories they already owned.

The User Guide

The Spectrum+ was supplied with a new User Guide, written by Neil Ardley and published by Dorling Kindersley.

The guide was markedly different from the original Spectrum documentation. Rather than concentrating primarily on detailed programming reference material, it used photographs, diagrams, illustrations and colour-coded sections to make the computer more approachable to newcomers.

The opening section, Get Going, concentrated on setting up the computer and dealing with common problems. Later sections introduced programming, graphics and sound before moving on to explanations of the computer's hardware and a BASIC reference.

The guide was attractive and easy to follow, although contemporary reviewers noted that it was less comprehensive than the original Spectrum manual. Experienced programmers were therefore likely to continue using the earlier manual as a more detailed reference.

The Companion Cassette

The User Guide was accompanied by a Companion Cassette containing programs intended to introduce owners to the Spectrum+ and its keyboard.

The cassette included a keyboard tutorial together with games and demonstration programs, giving new owners something they could immediately load and explore.

The combination of the illustrated guide and demonstration software reflected Sinclair's attempt to make the Spectrum more approachable to people who might previously have regarded computers as difficult or intimidating.

The official £20 upgrade

Sinclair Research also provided existing 48K Spectrum owners with a way of obtaining the new keyboard without purchasing another computer.

The official Spectrum Upgrade Kit was advertised at £20 and allowed a working 48K Spectrum to be converted to the Spectrum+ design. The conversion involved soldering several wires, with instructions supplied with the kit.

For owners who did not want to carry out the modification themselves, Sinclair Research offered an upgrade service for £30. Owners could return their computer to Sinclair, which would carry out the conversion and return the upgraded machine.

Both options included the new User Guide and Companion Cassette.

The official upgrade is an important indication of how Sinclair viewed the Spectrum+. Rather than treating it as a completely new computer, the company offered existing owners a relatively inexpensive route to the new case and keyboard.

Why the Spectrum+ mattered

The Spectrum+ was an unusual upgrade because most of its important changes were aimed at the way people interacted with the computer rather than what the electronics could do. The processor, memory capacity and BASIC environment remained essentially unchanged, while the new case and keyboard addressed criticisms that had increasingly been directed at the original Spectrum.

For programmers and users of business and educational software, the new keyboard was a substantial improvement. For games players, the advantages were less obvious because the original Spectrum could already run the same games, particularly when a joystick was used.

The market had already recognised the limitations of the rubber keyboard. Companies such as Saga, DK'tronics, Transform and Fuller had produced replacement keyboards and interfaces for the original Spectrum, demonstrating that there was considerable demand for a more conventional typing experience.

The Spectrum+ therefore helped modernise the appearance and usability of the machine without breaking the connection with the enormous software and peripheral ecosystem that had grown around it.

The ZX Spectrum+ 128K

The next major development was the ZX Spectrum+ 128K, introduced in Spain in 1985 and subsequently made available in other markets. It retained the general design of the Spectrum+ while introducing a much more substantial hardware upgrade.

The 128K machine added 128K of RAM, the AY-3-8912 sound chip and additional hardware and software designed to make use of the expanded memory. It also introduced a new extended version of Spectrum BASIC.

At the same time, Sinclair retained compatibility with the established 48K Spectrum software library. This allowed the new machine to benefit from the growing market for more sophisticated 128K software without abandoning the enormous collection of existing Spectrum programs.

The 128K Spectrum consequently marked a much more substantial technical development than the original Spectrum+. The + had concentrated mainly on the physical design of the computer, whereas the 128K model expanded the underlying capabilities of the Spectrum itself.

These machines retained the identity and software heritage of the Spectrum while introducing increasingly substantial changes to the hardware. The +2 incorporated a built-in cassette recorder, while the +3 introduced a built-in disk drive and a new disk-based operating environment.

The later +2A and +2B used much of the newer Amstrad hardware developed for the +3 while retaining the cassette-based design. The Spectrum+ therefore represents an important point in the transition from the original Sinclair Spectrum towards the later Amstrad generation.

Technical specification

Summary

The ZX Spectrum+ was not a completely new computer. Instead, it was Sinclair's attempt to modernise the successful 48K Spectrum while preserving the software, hardware and user base that had grown around it.

Its redesigned case, conventional keyboard and reset button addressed some of the principal criticisms of the original machine, while the official upgrade kit allowed existing owners to adopt the new design without replacing their computer.

More importantly, the Spectrum+ helped carry the original Spectrum design into the next stage of its development. The 128K Spectrum introduced a much more substantial technical expansion, and the later Amstrad machines would take the Spectrum even further with integrated cassette and disk systems.