4.4. Why not X?   

Given that X is the universal cure for all ills, why should anyone ever not use X?

The device independence and distributed nature of X does incur an overhead. On most Unix workstations approximately 16 MB of RAM is recommended for good performance in X. (DOS PC implementations of the X Window System normally require 2MB of RAM to even start and recommend 4MB of RAM for reasonable performance).

X also takes up more disk space than custom, hardware dependant windowing systems. On the Sun SPARCstation range, OpenLook plus all the programming libraries takes up about 30MB. Compare this to the fact that the SPARCstation 1 was only sold with a 100MB disk when it first came out, and that this was quite adequate when running the SunView windowing system.

On older systems, X may also incur a performance overhead. An example of this is with the Intergraph range of workstations. Their custom windowing system, EnvironV, had hardware support in their old series of machines (the 100 and 200 series). You can run the X Window System on these machines, but without the hardware accelerators the windowing system is sloooooooooow.

However, given that disk and memory prices are forever becoming cheaper, these limitations of X are not overwhelming ones. As far as I know all unix workstation vendors are currently selling their machines with an X based windowing system as standard.