Why The Dinosaurs Won't Die

DaveAtFraud writes "Ace's Hardware has a nice introductory article to the animal that will not die: The Mainframe. Ever wonder why these things are still around and what makes them different from a PC or UNIX box? The article is IBM-centric so there's no discussion of say the CDC Cyber series but when most people don't even believe that mainframes exist anymore, what the hay, let's disabuse them of that notion first. Hopefully, the author will follow up with the additional promised articles that go into more technical detail but this is a good place to start. I wonder if they still make card readers, too?" This guide came out last month, but it's worth looking through, even just for the pictures.

Comments

Re:Two words, Sequenced Transactions

[anonymous cupboard]

I think you misundertand, not only must the transactions be uniquely identified (this is easy), but the original ordering must be maintained (hard). Simply time stamping transactions would not be enough.

Currently the TSN is assigned through a cluster-wide 'semaphore' maintained by the distributed lock manager. However, one system at any time has the responsibility for logging the transactions (although the job can 'fail-over' to any other system. The design of the system means that every state change must be written out of the system so that if an individual system dies, the others can continue from the same point with no loss of information permitted unless a major disaster occurs.

Oh and you can forget databases as they tend to be rather slow. Recovery unit journalled ISAM files was the only way fast enough.

There may be a lot of CompSci Theory on this subject but there is very little that is relevant when you want a highly reliable system with several thousand transactions per minute.

Oh and this particular system is running the trading at CBOT, EUREX and XETRA.

Here's a good primer

[wiredog]

The April 1998 Byte cover story has a graphic Why PCs Crash, and Mainframes Don't. It's interesting to see how little has changed in almost 5 years.