The human stance on legal proscriptions is that when anything is outlawed, then only outlaws use/do it.  The more desirable the prohibited thing, the more people will be outlaws.

Unless the "laws" were such that they made people not *want* to use computing technology, people would surreptitiously be pushing at the edge of the proscriptions.  Where do you draw the line between electronics (or even mechanics) and computing?  How does law enforcement even recognize that a pile of components is actually a computer?

The main effect in my view would be that computers will be more primitive, and computer components would likely have other purposes that don't involve instruction processing, but a few seemingly unrelated items could be assembled into a computer.

That, however, assumes that your society is human and/or that proscriptions are things to be worked around.

It could well be that computers are simply thought to be impossible to make (or your society doesn't try to bend the rules), so no-one wastes time with them.  In that case, secretaries and counting-houses (filled with abacus-using calculation personnel) will be a major part of the workforce as they were some years ago - someone needs to do all the repetitive note-writing and calculating that is now done with computers.  They may not be particularly well-paid, but in those days, there was very little unemployment - even an employment shortage - finding a secretarial job was literally a matter of applying to a few companies and choosing which of the acceptances *you* would accept.