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Building a fast reliable fault tolerant system is easier on mainframes than the cloud you're familiar with.

Imagine having transactions ACROSS services. Do you know how much bullshit and over engineering that gets rid of? A lot.

in a nutshell a mainframe is a cloud in a box for high throughput workloads which need crypto and tpu accelerators.

mainframe pricing usually is not by pound of iron but per cpu cycle. unless you say nah I'm buying the thing, not just cycles. soyou have a choice of cloud pricing or hardware pricing.

for significant pure Linux workloads that need an own on premise cloud the TCO pricing is surprisingly competitive with any home grown solution.

even if you don't _need_ an own on premise cloud, AWS and similar donate come for free and there may be a break even there, too.

that said, legacy host software, Delphi, cics, Oracle, DB/2, cobol etc, you named it, yes that's a different story, with all the extra software licensing.

but a pure Linux mainframe is surprisingly competitive not just in compute and throughput but also in pricing.

plus you get quite some high availability in silicon. think ECC on the ALU, hot stand by spare CPU, multipath everything, if your business depends on uptime your system architecture becomes much simpler on highly dependable hardware.

so that spreadsheet compares own people and software construction vs IBM tax in some columns.

lol I start sounding like an IBM sales person https://www.ibm.com/products/integrated-facility-for-linux

I just did Linux on Z for a while and I loved it, so please bear my enthusiasm :-D

>but a pure Linux mainframe is surprisingly competitive not just in compute and throughput but also in pricing.

It's not competitive when you consider what long-time IBM mainframe customers actually do. E.g. SABRE airline and travel reservation system was one of the first IBM mainframe customers in 1960 with the IBM 7090 and then upgraded to System 360 and then the newer Z mainframes. SABRE's multi-decade experience with IBM mainframes with mission-critical business applications means they are one of the world's foremost experts on its capabilities & costs that's not biased by any IBM marketing or sales pitches.

Even with all that in-house experience, SABRE still chose to gradually migrate off of IBM mainframes to less expensive tech stacks. Some have touted IBM's TPF (Transaction Processing Facility) on the mainframe as compelling technology but that still didn't dissuade SABRE in ~2001 when they migrated the airfare pricing application to Tandem (Compaq/HP) NonStop servers running UNIX. (https://www.computerworld.com/article/1339621/has-mainframe-...)

They then started a 10+ year effort to migrate more mainframe workloads to Google Cloud. E.g. from https://www.sabre.com/insights/a-journey-to-tackle-legacy-co... :

> We moved 93% of compute capacity from physical data centers to the public cloud, resulting in a 50% decrease in our compute costs.

> We migrated more than 120 million bookings from a mainframe-based system to one using Google Cloud’s Spanner database, without impacting customer operations.

JP Morgan Bank is another example of migrating from IBM mainframes to cloud. If anyone out there truly thinks that running a new greenfield Linux workload will be be cheaper or even cost-competitive on a new IBM Z mainframe, just pause and consider if you truly know something about IBM mainframes' OpEx that multi-decade IBM customers like SABRE and JP Morgan don't already know.

Why would any new customers in 2025 willingly buy into IBM Z mainframes if they see existing customers spending billions trying trying to move off of them?

I’ve had to budget a line of business app that runs on both z/OS and AWS. Reliability for both hit an asymptote somewhere around 2019. The opex price crossover happened somewhere around the same time, depending on the customer.

Nearly every installation site and their internal support director agrees that the z/OS installations are far less expensive to support, simply because the minimum level of experience for a z/OS engineer is about a magnitude more than a cloud engineer.

So a more experienced engineer with a relatively rare skillset is less expensive? I think i'm missing something.

> Tandem (Compaq/HP) NonStop servers running UNIX

Nitpick: The OS these machines run is called Guardian. It does have a POSIX/Unixy subsystem/compatibility system called Open System Services.

It’s a risk issue. 5 year high risk projects aren’t appealing to CIOs with an average tenure around 18-36 months. Even if it works, why should the next asshole get the credit?

I think the point is that IBM’s market is shrinking, and they can’t acquire new customers. They will eventually need to stop making mainframes because there will be a crossover between the cost for new mainframes for remaining customers vs transition to commodity hardware cost.

Virtually no new tech startup with a greenfield project is going to pay Delphi $1599-per-seat for each of their developers. Only existing customers stuck with their investment in Delphi code are going to pay that.

I agree with this, and all your other reasons why mainframes will remain legacy platforms.

But man, how crazy is it that an industry that is 100% productivity driven and (until AI data centers, at least) labor-cost-constrained would snub its nose at paying a fraction of a percent of those developers’ salaries to put good tools in their hands.

All those times I've seen managers pooh-pooh RAM upgrades for machines used by people whose salaries might be 250-500x the machine...