Sinister Scrollbar in the Xerox Star Xplained

Alan Dix

School of Computing
Staffordshire University
Stafford, ST18 0DG, UK.

Full reference:
A. Dix (1998).
Sinister Scrollbar in the Xerox Star Xplained.
Interfaces, Summer 1998.
This short note is an update to:
A. Dix (1998). Hands Across the Screen - why scrollbars are on the right and other stories. Interfaces, Spring 1998.
See also:
my pages on why little things matter in interface design
discussion in comp.humanfactors on Why are the scrollbar placed at the righthand side of the document frame?

In my previous article "Hands across the screen - why scrollbars are on the right and other stories", I explained how the scollbar first moved to the right in the Xerox Star interface, but that I did not believe this was the correct place for it. Whilst at the CHI98 conference I was able to talk to David Smith, now of Stagecast Software, who worked as part of the Star design team.

He explained how the movement of the scrollbar to the right was not an accident, but a deliberate design decision. The reasoning was that precisely because the left-hand side of the screen is important for reading text it is also important to keep it clear of unnecessary visual clutter. Hence the scrollbar, that had been on the left in the Smalltalk and InterLisp environments, was moved to the right-hand side.

So, given my pronouncement that the right-hand side is a bad idea, am I wrong or were they?

In fact, the answer is that the Xerox Star scrollbar is fundamentally different from current scrollbars and hence the problems I highlighted with current right-hand scrollbars do not apply to the Star scrollbar.

Looking at the Star scrollbar (right), it has three types of control:

  1. the arrows which move the text a line at a time
  2. the +/- buttons which move the text a page at a time
  3. the scroll area with its diamond shaped 'handle'

The arrow and page up/down buttons are similar to current scrollbar buttons and the scrollbar 'handle' similarly allowed one to scroll to any point in the document. The major difference however between this and current scrollbars is that both kinds of large movement (2 and 3) moved to page boundaries. In each case the top of a page is aligned with the top of the screen. This is very similar to the redesign of the page up/down buttons in my previous article and the disorientation as one tries to match the old and new pages is thus not an issue. Only the line up/down buttons move the text to other, non-page-boundary offsets. This is also not a problem as the small movements make reorientation easy and for repeated line-by-line movement it is possible to position the mouse and then watch the screen as the mouse is clicked or held down for continuous scrolling.

As the Star evolved into the current Macintosh, Windows and X environments, the design changed to the current dragging form where the 'handle' is grasped by the mouse and moved to an arbitrary point in the document. The design changed, but the rationale for placement was not revisited leading to the current, unsatisfactory situation.

Another bit of design rationale that got lost in this transition was the direction of the arrows on the scrollbar. On most current scrollbars the line-by-line arrows point outwards whereas the Star arrows pointed inwards. In both cases pressing the upper arrow makes the window move upwards in the text (and hence also the scrollbar handle upwards). Recall, there is no obvious 'right' answer for this. If the arrows point outwards they match the movement of the handle, but the text moves in the opposite direction (as you move up the document the text moves down). If instead, the arrows point inwards they match the movement of the text on the screen, but oppose the movement of the handle (the downwards arrow moves you upwards in the document).

David Smith described to me how in the first version of the design documents for the Star, the scrollbar arrows pointed outwards as they do in modern interfaces. However, unsure of the correct orientation, the Star design team performed user studies with both orientations. Whereas the software designers were quite happy with the outwards form, the non-computing users were uniformly confused by this direction of arrows, hence the inwards pointing arrows were adopted for the final Star design. Unfortunately when the Star design documents were passed on to the later design teams for the Lisa and Macintosh, the initial, wrong version of the scrollbar designs was used! Hence we came by our current scrollbar arrow direction by accident and it is precisely the opposite of what was found to be easy to use.

In both these examples, we see that apparently minor design changes can radically affect the feel and behaviour of an interface widget. Little things really do matter.

Further info on the Star

David Canfield Smith and Charles H. Irby (1998) Xerox Star Live Demonstration. page 17. In CHI98 Summary, Claire-Marie Karat and Arnuld Lund (Eds).
Alan Dix 22/7/98