Nixon employed his first staff member in 2006 and in early 2007 opened an office in Wicksteed St.
In 2012 he opened an office in New Plymouth and in 2016 moved to the business's current premises in Glasgow St. He now employs 10 staff, seven of them in Whanganui.
"Some people think we're a big franchise because of the 'New Zealand' in our name but we're a small Whanganui-owned company," Nixon said.
"We can service anywhere in the country remotely. We work for clients all around New Zealand but predominantly in the central districts area. Alarm Watch in Whanganui would be one of our bigger clients. We do software and look after their IT.
"There are two sides to the business. One side is managing networks for businesses, particularly law firms.
"Some companies do 'break/fix' where they fix something when it breaks. We get a monthly fee and ensure nothing breaks so there's less disruption for the business. We are motivated to fix problems. It's a different mindset to a lot of other companies."
The other side of the business is Appmani which does software development and writes mobile applications.
NZCS has its own software applications and in 2017 released its online form creator, Easy Peasy Lemon Squeezy Forms.
There have been many changes in technology during NZCS's 20 years.
"People are a lot more reliant on their computer," Nixon said.
"Twenty years ago, if the computer wasn't working for a day it didn't matter. Now it's a problem. Downtime is expensive for a company.
"There are different sorts of problems. Things are more stable than they used to be but because there are more applications out there, there's more involved in fixing problems. We are constantly having to learn."
The NZCS staff were treated to a trip to Waiheke Island to celebrate the company's 20 years.
"It was a nice way to say thank you to the staff for making the company do so well," Nixon said.