Longest PCs

MORE THAN 1000 DAYS.
This list had been drawn from the IBM Vintage PCs table, which includes only "family one" (PC/XT, PC/AT) and PS/2 systems, and not PS/1s and PS/VPs, which were introduced in 1992. Also note that I left out all models whose exact announcement or withdrawal date is not available.

machine type	model	Announced	Withdrawn	Days
PS/2 Model 25	8525-001/-004/-G01/-G04	04/08/87	23/02/93	2030
PS/2 Model 25 Collegiate	8525-C02/-C05/-K02/-K05	04/08/87	23/02/93	2030
PS/2 Model 25	8525-L01/-L04	02/06/88	23/02/93	1727
PS/2 Model P70 386	8573-121	09/05/89	15/12/92	1316
PS/2 Model 30	8530-021	02/04/87	02/10/90	1279
PS/2 Model 80 386	8580-111	02/04/87	02/10/90	1279
PS/2 Model 30 286	8530-E01	13/09/88	04/02/92	1239
PS/2 Model 60	8560-041/-071	02/04/87	31/07/90	1216
PS/2 Model 80 386	8580-041/-071	02/04/87	31/07/90	1216
PS/2 Model 80 386	8580-311	04/08/87	02/10/90	1155
PS/2 Model 70 386	8570-121/-A21	02/06/88	11/06/91	1104
PS/2 Model 80 386	8580-A31	20/03/90	23/02/93	1071
PS/2 Model 70 386	8570-E61	02/06/88	23/04/91	1055
Personal Computer AT	5170-068	14/08/84	30/06/87	1050
Personal Computer	5150-104/-166/-176	19/06/84	02/04/87	1017
Personal Computer XT	5160-086	19/06/84	02/04/87	1017
PS/2 Model 30 286	8530-E21	13/09/88	11/06/91	1001

IBM, XT, AT, PS/1, PS/2, and PS/VP are trademarks of International Business Machines Inc.