Computer hardware is like any other tangible asset. When you make an outright purchase, you own the asset. (You may also lease or rent hardware rather than purchasing it outright.) You may also purchase related services (such as a maintenance contract) at the same time, or have other rights such as a guarantee.
Although software is delivered in tangible form (eg on a CD-ROM), the software 'code' itself is an intangible intellectual property, protected by copyright law. In general, you do not purchase software outright. While you may purchase a physical CD-ROM, you also purchase a licence allowing you to use the software in accordance with the terms of the licence. Ownership of the software remains with the copyright owner (eg the company which originally created the software).
If you commission bespoke software, or use a consultant to modify software for you, you should ensure that the contract specifies that you will own the copyright - otherwise, you may be unable to make further changes to the software without permission, and may have to make further payments to the original software developer.
When you purchase a computer system, the contract may involve a mix of these, and may include other organisations apart from the final supplier. As a simple example, if you buy a computer system, including some installed software, the supplier might sell you the hardware and various services (eg installation and configuration) but your use of the software could still be governed by a licence from the original software developer or publisher.
