370 Systems

Home Up 370-3115/3125 370-3135 370-3138 370-3145 370-3148 370-3155 370-3158 370-3165 370-3168 370-3195







Following IBM's success with the 360 range the 370 range followed. Obviously these machines were compatible with the 360's and their peripherals. This meant that customers could literally wheel in a new CPU and connect it to the existing peripherals and start processing. I will again concentrate on the machines that we have collected the front panels from, but it was the 370 range that started to see the end of flashing lights on IBM Mainframe computers.

The initial improvements were in the type of circuitry used, the 370 used MST chips. Faster and more compact than the SLT circuits of the 360. Micro code was no longer Read Only (the 155 still used ROS) but loaded via floppy disc and referred to as reloadable control store. At power up time the CPU would perform an Initial Microprogram Load (IMPL). This would make engineering changes and additional feature changes much easier to accomplish. The block Multiplexer channel was also announced, this was more efficient than the the old selector channels for high speed devices. DASD systems had Rotational Position Sensing (RPS). This allowed the DASD to disconnect from the channel whilst seeking, and we started to see the end of CORE storage.

IBM also introduced the Integrated Storage Controller (ISC) this unit mounted inside the processor acted as a DASD control unit, the ISC is described in the Standard Interface section. In the later series of 370 machines Extended Architecture (XA) was also provided lifting the old 16 Megabyte real storage constraint and allowing more flexible use of I/O.  Cache Memory also came into use to buffer the speed of the CPU and main memory. The Channel to Channel Adapter (CTCA) was introduced so that CPU,s could be linked via their channels. Another complete story would be the change in Operating Systems and Pricing.

The 370 series developed over a number of what I shall call sub series. It started with the range ending in 5 (3135). This series was then superseded by the 8's (3138). Similar machines but obviously additional features as you will see. Now the numbers game start's to get a little more complicated. The smaller systems were replaced with 4321's, 4331's and 4341's whilst the large systems turned into 3031's, 3032's and 3033's. Finally we had the 4361 and 4381's at the bottom and 3083's, 3081's and 3084's at the high end. And that's as far as I'm going because the hardware started to get pretty boring around the 4341 stage. (CPU's had turned into something looking like a large chest freezer).

One interesting point I would like to make is how IBM moves to new platforms. The 4331 used the same micro code as the 3138, the 4341 the 3148. The first 3032 was a repackaged 3168 the 3031 was made from the 3158. All of the 30xx range used directors to handle the I/O channels these were 3158 processors with a change of code. The first 3081-D was a repackaged 3033. Each time new technology would be used offering all of the environmental and reliability benefits or as IBM puts it Increased Reliability Accessability and Serviceability (RAS) but using proven working architecture.

The Major new components that the 370 range brought were:

M.S.T. Circuits faster and more compact than the S.L.T of the 360 (these were real Integrated Circuits)
Buffer or Cache Memory between the CPU and Main Memory
Block Multiplexer Channels and 3 Megabyte transfer rates.
Channel To Channel Adapters (CTCA) to loosely connect processors
Reloadable Control Storage to replace the old Read Only Storage of the 360's.

Below are the machines that we have Control panels for but I have also tried to put in details of all of the 370 range.

img0076_small.gif (4229 bytes)     img0073_small.gif (4045 bytes)    img0074_small.gif (4092 bytes)    img0075_small.gif (3933 bytes)    img0072_small.gif (4120 bytes)

        3135                        3138                         3145                      3148                        3155



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This page was last edited on 27/03/00