ZX Spectrum software

Because most British home computer owners used tape instead of disk storage into the mid-1980s,[10] most ZX Spectrum software was originally distributed on audio cassette tapes. The software is encoded on tape as a sequence of pulses that sound similar to the noises made by a modem. Since the Spectrum has only a rudimentary tape interface, data is recorded using an unusually simple and very reliable modulation - similar to pulse-width modulation but without a constant clock rate. Pulses of different widths (durations) represent 0s and 1s. A "zero" is represented by a ~244 μs pulse followed by a gap of the same duration (855 clock ticks each at 3.5 MHz) for a total ~489 μs;[11] "one" is twice as long, totalling ~977 μs. This allows for 1,023 "ones" or 2,047 "zeros" to be recorded per second. Assuming an even proportion of each, the resulting mean transmission rate is ~1,365 average bits/s. Higher speeds are possible using custom machine code loaders instead of the ROM routines.

In theory, a standard 48K program may take about 5 minutes to load: 49,152 bytes × 8 = 393,216 bits; 393,216 bits / 1,365 baud ≈ 288 seconds = 4:48 minutes. In practice, however, such a program usually takes between 3–4 minutes to load (because of different number of 0s and 1s encoded using audio frequency shift keying, and not all memory needs loading), and 128K programs could take up to 11:23 minutes to load. Experienced users can often tell the type of a file, e.g. file header, screen image or main block of code, from the way it sounds on the tape.[12]

The standard method of storing files on tape uses a combination of header and associated data blocks. Both types of blocks are preceded by pilot and synchronization signals, used to accommodate numerous physical variations present such as tape deck speed and distortion arising from tape stretching. Headers have a short size of 19 bytes (1 zero-value flag byte, 17 header information bytes, and 1 checksum byte), where the header information consists of a type byte, a 10-byte filename, a word data block length, and two word parameters. Depending on the type byte, the loader presents one of the follow messages: Program: <filename> for programs written in BASIC; Bytes: <filename> for machine code, screen dumps, etc.; or Character array: <filename> for an ASCII-encoded file.[13]

During standard loading and saving processes, the border of the screen flashes with cyan/red stripes for the pilot signal and yellow/blue stripes for the header and data blocks; which colour of the pair is used depends upon the bit that was last read from the tape. Pilot and synchronization signals are usually represented with a thick stripe size; on header and data blocks, the stripes are thinner. Striped border effects, as used in the standard loader or more complex ones (see below) can also be found on games written for other 8-bit computers, such as the Commodore C64, and the Amstrad CPC 464/664/6128 - which, as it used the same Z80 CPU, often received ports of loading routines originally for the Spectrum.

The Spectrum was intended to work with almost any cassette tape player, and despite differences in audio reproduction fidelity, the software loading process was designed to be reliable; nevertheless it was still possible for tapes to fail loading with the message R Tape loading error, 0:1. One common cause was the use of a cassette copy from a tape recorder with a different head alignment to the one being used. This could sometimes be fixed by pressing on the top of the player during loading, or wedging the cassette with pieces of folded paper, to physically shift the tape into the required alignment. A more reliable solution was to realign the head, which was easily accessible on a number of tape players, with a small (jeweller's) screwdriver.

Typical settings for loading were ¾ volume, 100% treble, 0% bass. Audio filters like loudness and Dolby Noise Reduction had to be disabled, and it was not recommended to use a Hi-Fi player to load programs. There were some tape recorders built specially for digital use, such as the Timex Computer 2010 Tape Recorder or Grundig CR 100 Data Recorder. The ZX Spectrum Plus 2 and 2A models are fashioned after an Amstrad CPC 464 and feature a built-in tape "datacorder".

It is possible to alter the colours between which the border alternates during loading, and/or to use more than two colours, in order to obtain more flashy visual effects during the loading process.

Complex loaders with unusual speeds or encoding were the basis of the ZX Spectrum copy protection schemes, although other methods were used including asking for a particular word from the documentation included with the game — often a novella — or the notorious Lenslok system. This had a set of plastic prisms in a fold-out plastic holder: the idea was that a scrambled two-letter code would appear on the screen, which could only be read by holding the prisms at a fixed distance from the screen courtesy of the plastic holder. This relied rather too much on everyone using the same size television, and Lenslok became a running joke with Spectrum users.

One very interesting kind of software was copiers. Most were copyright infringement oriented, and their function was only tape duplication, but when Sinclair Research launched the ZX Microdrive, copiers were developed to copy programs from audio tape to microdrive tapes, and later on diskettes. Best known were the Lerm suite produced by Lerm Software and Trans Express by Romantic Robot. As the protections became more complex (e.g. Speedlock) it was almost impossible to use copiers to copy tapes, and the loaders had to be cracked by hand, to produce unprotected versions. Special hardware, like Romantic Robot's Multiface which was able to dump a copy of the ZX Spectrum RAM to disk/tape at the press of a button, was developed, entirely circumventing the copy protection systems. "Snapshots" generated by these black boxes would later become the original filetype recognised by emulators - .SNA - although these memory dumps have been generally replaced by more complex files, incorporating original loading features and multi-level options.

ZX Microdrive cartridge

The ZX Microdrive system was released in July 1983 and quickly became quite popular with the Spectrum user base due to the low cost of the drives, however, the actual media was very expensive for software publishers to use for mass market releases (by a factor of 10, compared to tape duplication). Furthermore, the cartridges themselves acquired a reputation for unreliability, and publishers were reluctant to QA each and every item shipped.[14] Hence the main use became to complement tape releases, usually utilities and niche products like the Tasword word processing software and the aforementioned Trans Express. No games are known to be exclusively released on Microdrive, but some companies allowed, and even aided, their software to be copied over. One such example was Rally Driver by Five Ways Software Ltd.[14]

The CF has a harder casing than a 3-inch floppy; the metal door is opened by a sliding plastic tab on the right side.

Several floppy disk systems were designed for the ZX Spectrum. The most popular (excepting Eastern Europe,) were the DISCiPLE and +D systems released by Miles Gordon Technology in 1987 and 1988 respectively. Despite becoming popular and being reliable (from using standard Shugart disk drives), most releases were utility software. However, both systems had the ability to store memory images onto disk, snapshots, which later on could be loaded back into the ZX Spectrum and execution would commence from the point where they were "snapped", making them perfect for "backups". Both systems were also compatible with the Microdrive command syntax, which made porting existing software simpler.

The ZX Spectrum +3 featured a built-in 3" disk drive and enjoyed more success when it came to commercial software releases.

Most Russian releases since 1989 are made for the Beta 128 disc interface, the only system now in use there.

In addition, software was also distributed through print media, fan magazines and books. The prevalent language for distribution was the Spectrum's BASIC dialect Sinclair BASIC. The reader would type the software into the computer by hand, run it, and save it to tape for later use. The software distributed in this way was in general simpler and slower than its assembly language counterparts, and lacked graphics. But soon, magazines were printing long lists of checksummed hexadecimal digits with machine code games or tools. There was a vibrant scientific community built around such software, ranging from satellite dish alignment programs to school classroom scheduling programs.

One unusual software distribution method were radio or television shows in e.g. Croatia (Radio 101), Serbia (Ventilator 202), Slovenia (Radio Študent), Poland, Czechoslovakia, Romania, Lebanon or Brazil, where the host would describe a program, instruct the audience to connect a cassette tape recorder to the radio or TV and then broadcast the program over the airwaves in audio format. In former Soviet Union, mostly in Russia and Ukraine unauthorised radio operators (so-called radio hooligans) often exchanged software from cassette tapes for Spectrum and other popular computers by broadcasting it.

Another unusual method which was used by some magazines were 7" 33⅓ rpm "flexidisc" records, not the hard vinyl ones, which could be played on a standard record player. These disks were known under various trademarked names including "Floppy ROM", "Flexisoft", and "Discoflex".

Between October 1991 and February 1992 Your Sinclair published a list of what they considered to be the top 100 games for the ZX Spectrum. Their top 10 were:[18][19]

1. Deathchase
2. Rebelstar
3. All or Nothing
4. Stop the Express
5. Head Over Heels
6. R-Type
7. The Sentinel
8. Rainbow Islands
9. Boulder Dash
10. Tornado Low Level

Between August and December 1991 CRASH published their list of the top 100 ZX Spectrum games, including in the top 10:[20]

1. Rainbow Islands
2. Chase H.Q.
3. RoboCop
4. RoboCop 2
5. Dizzy
6. Target: Renegade
7. Magicland Dizzy
8. Batman: The Movie
9. Operation Wolf
10. Midnight Resistance

Techradar published their list of the best 30 ZX Spectrum games in 2012, underlining which games stood the test of time.[21]

1. Elite – Firebird Games
2. R-Type – Electric Dreams Software
3. Chuckie Egg - A'n'F Software
4. Manic Miner - Bug-Byte Software Ltd
5. Knight Lore - Ultimate Play the Game
6. Back to Skool - Microsphere
7. Football Manager - Addictive Games Ltd
8. Lunar Jetman - Ultimate Play the Game
9. Horace Goes Skiing – Beam Software
10. Boulder Dash – Front Runner
11. Sim City - Infogrames
12. Underwurlde - Ultimate Play the Game
13. Super Hang-On - Electric Dreams Software
14. Jet Set Willy - Software Projects Ltd
15. Rainbow Islands - Ocean Software Ltd
16. Tornado Low Level - Vortex Software
17. Ant Attack - Quicksilva Ltd
18. Chase H.Q. - Ocean Software Ltd
19. Deus Ex Machina - Automata UK Ltd
20. Lode Runner - Software Projects Ltd
21. Gauntlet - US Gold Ltd
22. Fantasy World Dizzy - Code Masters Ltd
23. The Hobbit - Melbourne House
24. Atic Atac - Ultimate Play the Game
25. Tetris - Mirrorsoft Ltd
26. Hyper Sports - Imagine Software Ltd
27. The Way of the Exploding Fist – Melbourne House
28. Daley Thompson's Decathlon - Ocean
29. Skool Daze - Microsphere
30. The Great Escape - Ocean