Pencomps were allegedly very popular in the period leading up to the Technocalypse, and definitely for some time thereafter. They are much rarer today, with ubiquitous access to the Known Net across much of the civilized Sephirotic empires. They remain in use, however, especially amongst those opposed to implantation-augments if not to all excessive technology.
A pencomp is a processing device which is usually networked to additional, more capable processing devices. It is typically a 12- 20cm tube some 1-2 cm in diameter, semi-pointed at one end. It typically has one 'activation' button on the blunt end, one or more status indicators, and can pick up input via the motions a sophont moves it through - as in writing.
While a small screen was standard in most of the early models, some older variants had no display capability, relying instead on networked items such as a monocle, audio output, or the like.
More advanced variants project a "display" on any flat monochrome surface which it alters with the motion of the pencomp to give it a stable appearance. This allows for traditional scrolling and clicking actions via the tip of the pencomp.
Additional Comments: 1) Early versions used short range wireless technology to network with an associated PC or PDA. Anything 'written' with the pencomp appeared on the display.
2) Later versions incorporated a built-in ink pen that extended or retracted as needed. (In some early nano-enhanced versions the ink doubled as an (auxiliary) battery)
3) Still later versions used first MEMS and later early nanotech to produced myriad effects:
a) Variable ink tip adjustable from finepoint to medium size felt tip.
b) Variable ink color, first within the pen itself, later with 'smart ink' that could have its color adjusted even after having been written down. Just place the tip of the pen against the ink and adjust a control.
4) Digital paper eventually replaced a defined display. Digital paper employed embedded processors and 'electronic ink' to initially produce B/W displays and eventually full color. Eventually the paper was designed so that any pencomp could link to it (perhaps by 'writing' a code word, circling it, and then tapping the circle firmly 3x or something similar) right 'off the shelf' either a single sheet or an entire notebook.
5) Eventually digital paper becames so cheap and ubiquitous that it was more difficult to purchase the non-digital form.
6) Digital paper eventually added in MEMS and nanotech to culminate in a display material with all the properties of paper (flexibility, light, common) combined with all the capabilities of a hi-resolution full color wireless-network computer display. Eventually, the issue of a 'display' for a pencomp became as meaningless as the need for a built in display for pens and pencils. Anything written/drawn on digital paper could be uploaded either into the pencomp or onto a website.
7) Those who wanted a more dedicated display used "video fabric". Turned off it had all the lightness and flexibility of a cloth handkerchief. Turned on it became as rigid as cardboard and had all the abilities of a computer display.