R S / 6 0 0 0   M a c h i n e   T i m e - L i n e

Sources: The RS/6000 Systems Handbook 2000 Edition & IBM Sales Manual
Machine types are in blue: 7012, and the year of announcement is given.
1990 The first RS/6000 was announced February 1990 and shipped June 1990 (7013-520&530)
7012 (20 to 200 MHz) Micro Channel Desktop Systems (withdrawn)
7013 (20 to 200 MHz) Micro Channel Deskside Systems
(withdrawn)
7015 (25 to 200 MHz) Micro Channel Rack Systems
(withdrawn, except R50)
1992 7011 (33 to 80 MHz) Micro Channel Workstations (withdrawn)
1993 9076/SP1 (withdrawn)
7008 (33 MHz) Micro Channel Desktop Workstation (withdrawn)
1994 7006 (80 to 120 MHz) Micro Channel Entry Desktops (withdrawn) 
7007 (50 MHz) Notebook! (withdrawn)
7009 (80 to 120 MHz) Micro Channel Compact Servers
(withdrawn)
7030 (59 to 67 MHz) 2D/3D Graphics Workstations
7020 (66 Mhz) Entry Workstation

9076/SP2
1995 7248 (100 to 133 MHz) PCI Workstations (withdrawn)
7024 (100 to 233 MHz) PCI Deskside Systems (withdrawn)
1996 7025 (166 to 500 MHz) PCI Workgroup Servers Deskside Systems
7026 (166 to 500 MHz) PCI Workgroup Servers - Rack Systems
7043
/43P (166 to 375 MHz) PCI Workstations & Workgroup Servers
SP2 renamed to SP
1997 7017 (125 to 600 MHz) PCI Enterprise Servers
1998 7046 (375 MHz) PCI Workgroup Servers - Rack Systems
2000 7044/44P (333 to 450 MHz) PCI Workstations & Workgroup Servers
2001 7028 (333 MHz to 1.45 GHz) Deskside & Rack-mount Systems
2001 7040 (1.1 to 1.7 GHz) Enterprise Servers
2001 1,200,000 systems have shipped
2002 9112 (450 MHz) Workstations
7038 (1.2 to 1.45 GHz) Rack-mount Systems
7039 (1.1 to 1.7 GHz) Rack-mount Systems
2003 7029 (1.2 GHz) PCI Deskside & Rack-mount Systems 

You can also take a look at RS/6000 Machine Type Models (table with Announced/Available/Marketing withdrawn/Replaced by information).