This question has a few answers to it. Specifically if you are asking this on the Varian Cary 50, it has a full range of 190 to 1100 nm it covers. So that is not of concern to this Spectrophotometer. I think your question is more oriented at Spectrophotometers in general. Since the Visible spectrum is considered in the 390 to 750 nm range, the UV range falls typically into 190 nm to 400 nm for most spectrophotometer analysis even though the UV spectrum is classified as 10 nm to 400 nm.

For Spectrophotometers, some designs incorporate a separate lamp for the Visible bandwidth and another lamp for the UV bandwidth. So you'll see some Spectrophotometers with two lamps, and these models are typically called UV/VIS or UV Visible. The Cary 50 with it's Xenon pulsed lamp covers the full range with a single lamp.

To answer the question directly as asked, a UV/VIS instrument will cover a wavelength range typically of 190 nm to 800 nm. A UV Spectrophotometer will cover the range of 190 to 400 nm.

The differences in the instrument will be seen in their performance specifications, specifically I think you need to look at the source lamp and the characteristics of the source lamp itself. Of course you need to look at the photomultiplier or PhotoDiodes/Diode Arrays for their characteristics. Diodes typically have very high sensitivity to visible light in comparison to the UV, so even though a Diode Array may use a deuterium lamp, the responsiveness of the diodes to the lower visible energy of D2 lamps provides a nice match making a visible lamp unnecessary for most applications. I personally love this combination for routine UV and VIS work and it's only one lamp, one detector with nice performance at all wavelengths.

If you want to push performance limits to the edge, a photomultiplier tube equipped instrument is going to be your choice, and this will be where you need to determine your lamp requirements and in some cases photomultiplier requirements.

At the end of the day, the way to answer your question properly is to understand what you want to analyze and concentrations of what you are looking for.