Commodore Datasette

A Datasette ( Commodore: Datassette ) is a widely used in the 1980s device to store computer data on conventional compact cassette (CC). Datasette is a portmanteau word from Data (English for data) and cassette. The term originally comes from Commodore, was later occasionally used for similar devices from other home computers, including Atari, Apple, Robotron, Tandy Sinclair, Texas Instruments and Amstrad / Schneider.

Disk

Specifically, there were designated as data cartridge tapes (for example the products or Magna Computape ), but these were expensive and gave less space than conventional cassette, so that in most cases commercially available audio tapes have been used as a data cartridge. In a conventional cassette with 30 minutes of around 100 Kbytes can be stored in the standard format of Commodore computers. Through the use of loading accelerators such as Turbo Tape roughly 1 MB per 30 minutes of tape can be stored. The bit rate is in the range of approximately 300 bit / s to just under 5 kbit / s

Disadvantages

Today datasettes no longer be used because they are inferior to the current media in terms of capacity and speed many orders of magnitude. In addition, almost all datasettes purely linear media, the tape stops from users must be studied by means of protracted spool by hand; they are thus the media with random access, such as floppy disks, hard disks or CD -ROMs, also inferior in principle.

Variants

Cartridge drives random access were represented only in the mid-range systems, especially in the 1970s; the only home computer, which possessed a cassette drive with random access, apply the Philips P2000M from the year 1980, and the portable Epson HX -20 and PX -8. Both used the mini cassette developed by the manufacturer for Dictation and designed for the Start-/Stopp-Betrieb. There, both brought about 170 KB of data under.

There were also a number of drives that used special cartridges with a continuous belt, such as the Sinclair Microdrive the company, or the more exotic Entrepo Quick Data Drive for the Commodore 64

Distant relatives of Datasette are drives that store the data on VHS video cassettes or video -8 tapes. These were not used because of their high price at home computers, but were partially in the professional area for data backup large archives used because they offered an extremely high storage capacity for that time ( on a 240 -minute VHS tape was in the mid- 1980s on 2 gigabytes of storage, which at that time the contents of several dozen disks corresponded ). Tape drives of this type are also referred to as a " streamer ".

The first digital synthesizer (and some storable analog synthesizers like the Korg Poly 61) often possessed a socket for connecting a tape recorder or a tape recorder, over which individual presets were stored on tape or cartridge and recall. As with the instrument itself does not control the drive has been made, each suitable for recording audio medium could be used in principle. The media used in the recording studios varied with time and as well as digital formats such as DAT, DCC and MiniDisc were often used. Lovers of classic synthesizers save your presets today usually via the audio port of a personal computer.

The Datasette 1530/31 of Commodore was 0.7 kg heavy and 19.5 cm wide, 5 cm high and 15 cm deep.

Technology

To build the Datasette the drive, the preamplifier and the heads of a normal music cassette recorder be used on speaker and microphone will be omitted. As an additional element, it has a demodulator, which in this case is a Schmitt trigger and is used to determine the zero crossings of the received signal.

The data is usually (exception: Atari ) stored with a modified frequency shift on the tape, as shown in the adjacent figure. In this recording, the amplitude carries no information. Reading and decoding according to the Schmitt trigger, the time intervals between the positive and negative zero crossings of the signal on timer modules, such as the MOS Technology CIA ( 6526 ) were measured and recovered from this period information, the data information. In the drawing on the important data for the reconstruction of negative zero crossings of the signal are shown as black circles on the center line. Depending on the time interval so the two values ​​can be logic 1 and logic 0 distinguished.

Bits thus received are then individually shifted in a shift register and compared continuously at the beginning of a data transfer with special bit sequences for synchronization. The first byte of such a sequence for synchronization start of the block is referred to as the lead-in byte followed by multiple sync bytes which are used to compensate for possible flutter of the tape through the coordination of timers. For example, use the Turbo Tape 64 used on the Commodore 64 as a lead-in byte 0x02, followed by the sync sequence 0x08, 0x07, 0x06, 0x05, 0x03, 0x02, 0x01. This was followed by the actual user data.

Devices from the company Atari used a direct frequency shift keying. Instead of recognizing and measuring the time spacing of the zero crossings of the signal, two fixed frequencies, which stood for the bit values ​​0 and 1, filtered by bandpass filters from the audio signal and comparing their amplitude were during playback; the respective stronger signal determined the output from the Atari Datasette logic level. Quick - charging programs could be with the Atari datasettes not use because the most properties of the recording format were unchangeably set by the hardware of these devices.

On some computer models (among Apple II and the Sinclair models), there were no matching specific datasettes from the same manufacturer. Instead we use any commercial audio cassette player could be connected via the audio inputs and outputs, the demodulator was in this case the computer itself to recording, it is important that the tape head is properly adjusted, typically uses only a mono track with a typical bandwidth of around 10 kHz. An exception are the devices manufactured by Atari, which brought under one music track to the accompaniment of charging on a stereo track, the data on the other. Flutter, the move from the drive and the cartridge were either compensated by correspondingly low and thus more robust data rate, or in some quick chargers through special, constantly repeated synchronization sequences that were repeated depending on the procedure and within blocks of data at runtime.

Also in the original IBM PC and the IBM PCjr a Datasettenport was present, which, like the keyboard port was designed as a 5 -pin female DIN round plug connector. However cassettes were considered as storage media already on the introduction of the IBM PC for the targeted market segment as obsolete; also could be accessed directly on the Datasette only on the internal ROM Basic IBM - PC, but not on the much more powerful and most commonly used DOS. For these reasons, the interface was hardly used and there was, unlike in previous minicomputers, no market for prerecorded cassettes program. For this reason, the interface was at the immediate successor to the IBM PC, XT, is no longer used.

On the part of the PC BIOS was held the programming interface for application programs very simple and consisted of four functions of the software interrupt 15h. This made ​​it possible to start the drive motor ( function 00h, AH = 00h) to stop (Function 01h, AH = 01h) and reading (function 02h) and Write (function 03h) a certain number of bytes on the tape, which in CX had to be specified. In ES: BX pointer was to mention the memory address of the data buffer. Since DOS - in contrast to the floppy drives - offered no further routines for Datasette, only the low-level access routines of the BIOS for the use of the interface were by programmers and users are available, which own way of managing the data had to be found on the cassette. After the disappearance of the interface 15h of the interrupt has been used for other purposes in the PC - successors. For the PC AT an attempted call to the Datasettenroutinen could even lead to a system crash.

Applications

Can be saved, depending on the home computer, in various file formats. Even Written programs were often referred to as a single BASIC file. Commercial programs and games existed, as well as floppy disks programs, usually from multiple files (title graphics, more levels), which were then reloaded and were often stored in machine language. On the back of the tape often was an identical copy of the game or more levels.

Emulators use almost only tape images, such as. TAP and. T64, rarely, true sound files such as. WAV.

In the television program WDR Computer Club Audio signals were sent a so-called hard- rock bit in BASICODE that absorb you and could read by Datasette.

Gallery

Datasette for Commodore CBM 3008 (1982)

Datassette Commodore 1531

A clone version of the Commodore Datassette

Commodore PET (office computer ) with integrated Datassette

Luxury design for Office Environment

Atari Datasette XC 12

Compact cassettes were made ​​specifically for datasettes; here by the company Computape