Although Atlas 1 employed a six-bit character, a total of 124 characters could be represented. This was achieved by use of two distinct character sets (known as the outer and the inner sets) each comprising 62 characters. The remaining two characters were used to switch between the sets. Thus the sequence

The quick, brown fox

T<shift outer>he quick<shift inner>,<shift outer> brown fox

The emulator maps Atlas 1 characters onto the equivalent Windows characters as far as possible. This enables input to be prepared using a standard Windows text editor such as Notepad. Letters (upper and lower case) and digits are treated in this way, alongside the following list -

( ) , £ ? & * / < > = + - . ' : [ ] _ | ½ % ; ² α β space and tab

Shift to Upper Case

Shift to Lower Case

Stop

Punch On

Punch Off

ø , ⇾, ≥, ≠, ~, ⒑, ⒒ (all as single characters)

Then, there is the issue of backspace. The emulator maps the Atlas 1 backspace character onto the Windows \ symbol. The Atlas backspace character was used (on 7/8-track paper tape) as a means of representing compound characters, where two characters occupying the same position combined to form a special, ‘compound’ symbol. Thus the Atlas Autocode/Algol delimited word

begin

begin\\\\\_____

_____\\\\\begin

b\_e\_g\_i\_n\_

abcd\\\\ӾӾӾӾ

None of the facilities in this section were supported for punched card input. However, in the emulator, this restriction is relaxed if Lax mode is in use.

Lastly, if an Atlas program wished to output to a lineprinter (where backspace was not supported), it might write two records

begin

_____

Although the subterfuge of using ‘\’ to represent backspace might be acceptable for occasional use, its frequent use to indicate underlining in high-level languages makes the provision of alternative arrangements in the emulator useful. Text to be input to the emulator may be prepared in a word-processor such as Word or Wordpad instead of Notepad and so input to the emulator as a simulated paper tape. By using a subset of Word’s capabilities and saving the file in Rich Text Format (RTF), a more user-friendly approach may be taken. The text can be read by the emulator as a simulated paper tape document and the emulator will detect underlined text and convert it into the equivalent paper tape sequence of backspaces and underline characters. In a similar fashion, the use of Erase may be emulated using Word’s “Strikethrough” facility. We might then write abcd\\\\ӾӾӾӾ as abcd.

In addition, the symbol ≠ (not equal) (=\/ or =\|) can be expressed using the # symbol. A more elegant mapping for ≠ is available but # has the advantage of presence on the keyboard. In a similar manner a number of “unusual” characters which are available to Word users may be employed for paper tape input for convenience and for clarity when viewing the files. Click Special Character Support below for more detail. Click The Full Atlas Character Set below for the full list of Atlas 1 characters as listed in the ABL manual. Note that other character styles such as italic or bold are ignored and the use of other RTF constructs such as superscripting may produce unpredictable results.

The table below gives the list of characters supported on each of the peripheral types. Note that this is not quite the same as on the original machine.

* Lower case letters sent to the printer were rendered in upper case.

Note that, in Lax mode, all characters are supported on all devices.