Table:
| ($ in millions) |  |  |  |
| --- | --- | --- | --- |
| For the year ended December 31: | 2018 | 2017 | Yr.-to-Yr. Percent/ Margin Change |
| Systems |  |  |  |
| External Systems Hardware gross profit | $2,590 | $2,893 | (10.5)% |
| External Systems Hardware gross profit margin | 40.7% | 44.6% | (3.8)pts |
| External Operating Systems Software gross profit | $1,412 | $1,469 | (3.9)% |
| External Operating Systems Software gross profit margin | 84.5% | 86.4% | (1.9)pts. |
| External total gross profit | $4,002 | $4,362 | (8.2)% |
| External total gross profit margin | 49.8% | 53.2% | (3.4)pts. |
| Pre-tax income | $ 904 | $1,128 | (19.9)% |
| Pre-tax margin | 10.2% | 12.6% | (2.4)pts. |
Paragraphs:
The Systems gross profit margin decrease year to year was driven by the mix away from IBM Z and margin declines in Power Systems and Storage Systems.
The pre-tax income decline was driven by the strong performance in IBM Z in the prior year and the continued investment in innovation across the Systems portfolio.
Question:
What led to decrease in pre-tax income?
Answer: The pre-tax income decline was driven by the strong performance in IBM Z in the prior year and the continued investment in innovation across the Systems portfolio.