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Mobile Computers

$\mathcal{CELCUS\ ULTRA\ POSSE\ NEMO\ OBLIGATUR}$

In my environment mobile computers should be self-contained, i.e., they should be fully functional computers with their own operating system (e.g., Windows95, OS/2, or Linux) and applications--allowing the user to work independently from other machines (e.g., servers). In my particular case the operating system chosen is Linux, since it is currently in use on the mobile computers used in connection with the AMIGOS project, and it has sockets. In the long run any operating system providing a socket abstraction (in C),^2.1 so in this sense the mobile computers supported are heterogeneous.

In Bayou [53] the mobile computers must run some sort of Posix compliant operating system (actually, it could run in the same setting as mine) which confines the use to some sort of UNIX-clone.

In Coda [22], [42] the mobile clients are not allowed to be heterogeneous, in fact, they do not even come with their own operating system, thus making it necessary to cache system files on clients in order for them to work during periods of disconnection from the server(s). Personally, I would find it a bit absurd (and terribly annoying), if the machine I was using, stopped working for the lack of some obscure system file that I have never heard of. This problem can be tricky to handle^2.2 and even nearly impossible [25].

The people behind the SEER [26] predictive caching system (an extension to Ficus) also caches system files (i.e., the mobile clients are not heterogeneous), and they have found that "interrelationships among programs are complex and deliberately hidden", and therefore users cannot be expected to provide accurate specifications of critical files to cache.

I expect that the need to track down file usage as in Coda (by use of a help utility) or as with SEER (by constantly logging file references) is avoided altogether in my system because all (necessary) system files will be available on the mobile clients as they are self-contained, i.e., come with their own operating systems.

As another part of the AMIGOS project a system MIo-NFS [9] (Mobile Integration of NFS) that integrates mobile computing with NFS has been developed. That system is also heterogeneous in the sense that the clients only have to provide NFS--and nowadays you can even get NFS for PCs [49].

Everybody can agree on the fact that a mobile computer should be small, light and at least to some extent handy. Making them that way necessarily means that they become inferior to stationary workstations or desktops in terms of processing power (CPU & RAM), storage capacity (harddisk), and user interface (screen & keyboard). These factors as well as the question of limited power supply will be discussed in the following subsections.

Footnotes

...C),^2.1

It could, I have been told, equally well have been Windows and winsockets, i.e., the socket facility provided with the former, but I found it best (at first, anyway) to stick with the existing systems.

... handle^2.2

In Coda [42] they have even developed a special spy program to track down use of files during a session.

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