With the recent economic downturn it must have been tempting for many firms to delay upgrading their PC estate. Yet on the other side of the coin analysts will point out that sweating PC assets for too long could have a detrimental effect on staff productivity, and also actually cost more money because older PCs are less energy efficient and have a higher management and security burden. So when should a company bite the bullet and upgrade their fleet of ageing computers?

A study of 109 enterprises in the UK, US and Germany by IT services firm Wipro last year found that the optimal refresh rate is three years, based on a study of the cost of ownership of both PCs and laptops. The company noted, for instance, that the average cost of PC maintenance was 59% higher in a four year-old PC than a one year-old computer. It found that patches and application updates were far more likely to fail with older PCs. It also found that the cost of removing viruses from a five year old PC was twice that of a year-old computer.

Those costs, together with the energy savings from more efficient hardware, meant that hanging on to PCs for more than three years was a false economy according to its research. It found that the payback from moving to a three-year refresh cycle would come within 14 months for laptop PCs and 19 months for desktop PCs, if they were priced at $950 and $700 respectively.

Interestingly, the optimal time to refresh the PC estate has not changed dramatically since a study by analyst firm Robert Frances Group back in 2005: the magic number was found to be 30-40 months, or about three years.

But the firm also advised that while companies could optimise their refresh cycles using up-front PC purchasing, it would be even more effective to use leasing to optimise the PC refresh cycle: "Leasing can be a powerful tool to help maintain this desired refresh period. Leasing can lead to predictable spending patterns. It can also help to introduce best practices and technologies for PC management, and reduce support requirements by streamlining system images," said Robert Frances Group. "Additionally, leasing can help eliminate upfront costs and meet CFO and financial team cost drivers. IT and other business executives should consider leasing as an effective tool in reducing PC TCO costs by promoting a three-year PC refresh period, while obtaining preferential lending rates." Good news perhaps for the likes of Lombard Technology Services who specialise in IT leasing.

A similar study of 200 PCs at a financial services organisation in the UK by Intel and A.T. Kearney looked at whether a three year, or five year PC refresh cycle produced the lowest total cost of ownership (TCO). As well as looking at the various costs involved it surveyed the 200 users of those PCs, which ranged in age from brand new to over six years old, to find out what the user experience was like for different ages of computer.

They found that following a three year refresh cycle saved between $450 to $500 per user per year over a five year refresh cycle – meaning that a firm with 50,000 people could save up to $25 million per year by using a three-year refresh cycle instead of a five-year cycle. It also found that users with PCs that were four years old experienced twice as much downtime, and made twice as many calls to the IT help desk, than those whose machines were three years old. Yet there was very little difference in downtime or help-desk calls for those whose machines ranged between a year and three years old.

All three studies found that the optimal time to refresh the PC estate is three years. Two final metrics worth considering from the A.T. Kearney and Intel study: users with PCs older than four years lost data three times more often than users with PCs that were less than three years old, and users with PCs older than four years had security breaches three times more often than users with PCs less than three years old – ouch!