21. Other intangible assets
| Acquisition intangibles | Databases US$m | Internal use software US$m | Internally generated software US$m | Total US$m | |||
| Customer and other relationships US$m | Acquired software development US$m | Marketing- related assets US$m | |||||
| Cost | |||||||
| At 1 April 2021 | 1,505 | 401 | 100 | 1,345 | 327 | 1,042 | 4,720 |
| Differences on exchange | 9 | 2 | 5 | 90 | 1 | (8) | 99 |
| Additions through business combinations (note 41) | 207 | 105 | 9 | (1) | 1 | (6) | 315 |
| Other additions | — | — | — | 180 | 29 | 236 | 445 |
| Disposals | (87) | (11) | (6) | (99) | (11) | (74) | (288) |
| At 31 March 2022 | 1,634 | 497 | 108 | 1,515 | 347 | 1,190 | 5,291 |
| Accumulated amortisation and impairment | |||||||
| At 1 April 2021 | 721 | 266 | 85 | 923 | 251 | 508 | 2,754 |
| Differences on exchange | 9 | 3 | 6 | 69 | — | (8) | 79 |
| Charge for the year | 116 | 54 | 4 | 162 | 29 | 167 | 532 |
| Disposals | (87) | (11) | (6) | (99) | (11) | (74) | (288) |
| At 31 March 2022 | 759 | 312 | 89 | 1,055 | 269 | 593 | 3,077 |
| Net book amount at 31 March 2022 | 875 | 185 | 19 | 460 | 78 | 597 | 2,214 |
| Acquisition intangibles | Databases US$m | Internal use software US$m | Internally generated software US$m | Total US$m | |||
| Customer and other relationships US$m | Acquired software development US$m | Marketing- related assets US$m | |||||
| Cost | |||||||
| At 1 April 2020 | 1,094 | 337 | 91 | 1,311 | 376 | 860 | 4,069 |
| Differences on exchange | 25 | 8 | (2) | (13) | (2) | 35 | 51 |
| Additions through business combinations | 386 | 57 | 11 | 8 | 1 | 18 | 481 |
| Other additions | — | — | — | 147 | 30 | 197 | 374 |
| Disposals | — | (1) | — | (108) | (78) | (68) | (255) |
| At 31 March 2021 | 1,505 | 401 | 100 | 1,345 | 327 | 1,042 | 4,720 |
| Accumulated amortisation and impairment | |||||||
| At 1 April 2020 | 617 | 224 | 81 | 882 | 300 | 382 | 2,486 |
| Differences on exchange | 10 | 5 | (2) | (8) | 1 | 20 | 26 |
| Charge for the year | 94 | 38 | 6 | 157 | 28 | 141 | 464 |
| Impairment charge | — | — | — | — | — | 33 | 33 |
| Disposals | — | (1) | — | (108) | (78) | (68) | (255) |
| At 31 March 2021 | 721 | 266 | 85 | 923 | 251 | 508 | 2,754 |
| Net book amount at 1 April 2020 | 477 | 113 | 10 | 429 | 76 | 478 | 1,583 |
| Net book amount at 31 March 2021 | 784 | 135 | 15 | 422 | 76 | 534 | 1,966 |
Within the above are the following individually material assets at 31 March 2022:
- North America Healthcare customer relationships have a net book value of US$160m and a remaining amortisation period of six years.
- North America Tapad, Inc. customer relationships with a net book value of US$143m and a remaining amortisation period of 16 years.
- The former Risk Management division of AFS customer relationships with a net book value of US$126m and a remaining amortisation period of 11 years.
In addition to the development capitalised above we charged US$281m (2021: US$138m) of research and development costs in the Group income statement.
The impairment charge in the year ended 31 March 2021 largely related to an internally generated software asset in the UK and Ireland identified as requiring impairment due to a planned upgrade of our technology estate.