What is it?
For a technology that has been pronounced dead with tedious regularity every time some new innovation is launched, the mainframe is looking surprisingly healthy.
First, the minicomputer was going to kill it off and then client/server computing. But users soon discovered that distributed computing and the client/server model were expensive to manage and less reliable and scalable than they had been led to believe. In consequence, the mainframe re-emerged as the Enterprise Server.
Then, as thin-client became the dominant model, mainframe-centric computing found itself back in fashion, with PCs and other intelligent devices in place of the traditional green screens.
Users who had distributed their storage along with their servers found it was cheaper and easier to manage if it was all piled back into the datacentre, under the protection of the mainframe's 99.999% availability, and the watertight disciplines that have grown up around mainframes over decades. Frequently you will find Unix and NT servers doing a lot of the work, but relying on the mainframe for data.
The number of mainframe mips (millions of instructions per second) being sold is increasing year on year. IDC gives an industry figure of 40% growth. Hitachi claims 60% growth, and IBM 70%.
However, much of this growth is being driven by existing S/390 users, many of whom are consolidating the workload of mid-range servers that had originally been intended to replace the mainframe. IBM says more than 70% of corporate data is managed by the mainframe.
Most sites still use traditional skills such as Cics and Cobol, but these days the mainframe is just as likely to be acting as a Web server, running Websphere or SAP.
Where did it originate?
In 1964, with IBM's first mainframe, the System/360. The 370 followed, and the newest generation was ushered in with the System/390, in 1990.
What is it for?
Serious computing, where heavy-duty transaction processing is involved.
Where is it used?
In large enterprises.
What makes it special?
Its reliability, availability, scalability and manageability, which have never been equalled by any other processor architecture. Although mainframe hardware and software is expensive, performance is better on big systems, and services can be provided more economically if they are shared between multiple applications.
How hard is it to master?
At first sight, mainframe terminology may seem bewildering and daunting - and it is. Even if you have heard of Cics, what about IMS, Jes, TSO or JCL - the long list of things you need to know to build an application on S/390?
But things are changing, as IBM standardises on development tools and platforms throughout its server range. The way forward is with Java and IBM's Component Broker, which lets programmers write business logic without having to concern themselves with the infrastructure.
Not to be compared with
A shipping container, as in the early days. Some of us remember when a mainframe looked like a mainframe.
What does it run on?
Hitachi and Amdahl both make S/390-compatible mainframes, sometimes leapfrogging IBM with the power and functionality they can offer.
Few people know that
Water cooling systems were once used to stop mainframes overheating. According to Xephon, when ex-IBM chief John Akers told staff to "stop standing round the water cooler", salespeople assumed he meant them to stop pushing the mainframe and sell Unix instead.
What's coming up
The S/390 Application Development Solution, a mainframe-based bundle that will enable customers to build and deploy e-business applications. It includes both Cics/Cobol/DB2, and Visualage for Java and Websphere. Echoes of IBM's disastrous AD Cycle may cause palpitations in older staff.
Rates of pay
The classic Cobol/Cics/DB2 combination is still in demand, and while £25,000 to £35,000 is the usual range, a recently advertised analyst programmer position was offering up to £45,000. With Web skills on mainframe-based systems in the financial sector, the ceiling goes up to £50,000 - although you could make more as a contractor.
IBM is the obvious source for information on mainframe training but, while the independent mainframe training sector is not what it was, you can still find competitive alternatives.
If you are looking for independent options on the Web, it is worth trying www. amdahl-education.com, www.knowledgepool.com, www.bminternational.co.uk, or the Association of Independent Computer Specialists www.aics.org.uk.