No “real” S/390 hardware is required, although there are options to attach parallel and ESCON channel devices.4 No special adapter cards or other hardware is needed for basic S/390 emulation. The emulated S/390 runs as a Linux process, in the virtual memory provided by Linux. Every S/390 instruction that is executed is interpreted by the FLEX-ES emulation program, which then uses PC instructions to emulate the effects of the S/390 instruction.5
ThinkPad/EFS is not intended as a production S/390 machine. Many reasons are involved, including obvious ones such as:
No RAID protection is available for emulated S/390 disk volumes.
Total disk space is limited, as is the configuration of the disk space.
No S/390 channel connectivity is supported.
Memory is limited and must be shared between S/390 use and all the Linux-based processes.
The system is intended as a small development machine, a demonstration machine, and may fit in a number of debugging situations. It is definitely a multi-user system, with, for example, TSO users connected through TN3270 sessions.
1.2.1 FLEX-ES
FLEX-ES is a product of Fundamental Software, Incorporated, (FSI) of Fremont, California. ThinkPad/EFS systems are a cooperative effort involving IBM, FSI, and several business partners that market ThinkPad/EFS systems. FLEX-ES runs under Linux or several UNIX operating systems.
FSI also produces four hardware options that may be used with FLEX-ES. These are:
A parallel channel adapter, providing one S/390 parallel channel
A parallel channel adapter, providing three S/390 parallel channels
An ESCON channel adapter, providing one S/390 ESCON channel6
A communications adapter, providing six lines corresponding to S/370 ICA lines
These adapters are full-length PCI adapters and would not normally be used with a laptop machine. In principle, it may be possible to use one by installing it in an appropriate ThinkPad docking station. At the time of writing, such options had not been tested and must be considered unsupported; furthermore, the required FLEX-ES support modules are not provided with ThinkPad/EFS systems. This redbook ignores the FSI hardware adapters. If you are interested in these, you should refer to the NetFinity/EFS redbook.
FLEX-ES is a licensed product. The licenses are arranged through IBM and FSI business partners. A FLEX-ES license specifies the number of PC processors that can be used for S/390 emulation. For the ThinkPad/EFS system described in this redbook, this will specify a single processor. A FLEX-ES license is keyed to a specific serial number in a hardware dongle that is connected to the USB port of the ThinkPad and will run only in a ThinkPad that has this dongle installed. It is provided as part of the FLEX-ES license. A FLEX-ES license is also keyed to a specific PC Server (ThinkPad) speed, and will operate only on a server that operates within 2% of the specified speed.
4At the time of writing, there is no practical support for these adapters on a ThinkPad. We mention them here for completeness.
5This is a very brief statement of a complex process. FLEX-ES internally uses a “just in time” compiler technique to build PC code that emulates the S/390 instructions. A controlled amount of the “compiled” code is retained to improve performance within loops and so forth.
6This adapter was not yet available at the time of writing.
