What does "Subject to" + verb mean?
Part of the problem may be that this usage pertains to the adjective subject rather than the verb.
One definition at dictionary.com for the adjective is:
19. open or exposed (usually followed by to ): subject to ridicule.
"These computers are subject to change" means the computers are open to change.
Another part of the problem with this usage may be the alternate definitions:
Some other definitions at dictionary.com for the adjective are:
20. being dependent or conditional upon something (usually followed by to ): His consent is subject to your approval.
21. being under the necessity of undergoing something (usually followed by to ): All beings are subject to death.
The range of definitions from "open to exposed" to "being dependent or conditional upon" to "being under the necessity of undergoing" almost seems designed to confuse.
There seems to be a bit of a misunderstanding: change is a noun here, not a verb.
As Krueger has explained, the adjective subject + to + noun x normally means "exposed to x / open to x / susceptible to x".
So your example these computers are subject to change could mean something like this:
These computers may be changed ("are open to change/changes").
But I must say I find the use of subject to change with computers a bit odd: when something is said to be subject to change, it is usually some statement or position or document, not really a physical object like a computer. But of course in an unusual context it is possible.
It means that verb can happen to it. Change can happen to computers, or computers can be caused to undergo or endure change.
It bears mentioning that, while you can say subject to [verb], "subject to change" itself is a rather common phrase that just means "[noun] might change in the future."
The English phrase "X is/are subject to Y" has three different common meanings:
Y is required for X to happen or regulates the manner in which X can happen. "The merger is subject to shareholder approval." "U.S. action in Libya is subject to the War Powers Act."
Y is a process that often happens to X. "Battery contacts are subject to corrosion."
Y is thing that may act on or become associated with X. "Specifications are subject to change." "Are tablets subject to malware?"