| Number | Date | Country | Kind | 
|---|---|---|---|
| 62-4741 | Jan 1987 | JPX | |
| 62-21030 | Jan 1987 | JPX | 
| Number | Name | Date | Kind | 
|---|---|---|---|
| 4399502 | MacDonald et al. | Aug 1983 | |
| 4604690 | Crabtree et al. | Aug 1986 | |
| 4665555 | Alker et al. | May 1987 | |
| 4755808 | Bullock et al. | Jul 1988 | |
| 4772882 | Mical | Sep 1988 | 
| Entry | 
|---|
| Ralston, Anthony ed., Encyclopedia of Computer Science and Engineering, 2nd edition, 1983, pp. 779-789. |