IBM Z mainframes use Z processors and now Telum, Telum II processors, not POWER.

z Series have used both, POWER and TELUM (I and II) processors.

For many years, the 64-bit extension of the original S/360/370/390 architecture was emulated in the software layer via the static binary translation – just like the i Series AS/400 have been doing since the inception, and there was no native S/360 implementation in silicon for a fairly long time.

If my understanding is correct, with TELUM processors, IBM has gone back to implementing the ISA in silicon, although the available details on TELUM are scarce.

This (and variations) is commonly believed but not the case - IBM's Z hardware has always used processors which natively implement the Z instruction set. I think part of the source of the confusion is a presentation from years ago which showed that some IP is shared between the Z and Power CPUs.

> a presentation from years ago which showed that some IP is shared between the Z and Power CPUs.

The eCLIPz project, for the POWER6 & Z10[0].

"The z10 processor was co-developed with and shares many design traits with the POWER6 processor, such as fabrication technology, logic design, execution unit, floating-point units, bus technology (GX bus) and pipeline design style, i.e., a high frequency, low latency, deep (14 stages in the z10), in-order pipeline.

However, the processors are quite dissimilar in other respects, such as cache hierarchy and coherency, SMP topology and protocol, and chip organization."[1]

[0] https://news.ycombinator.com/item?id=18494225

[1] https://en.wikipedia.org/wiki/IBM_z10

Your understanding is not correct.

IBM z15 mainframes had z15 chip now they have Tellum. z chips are their own line. z14, z13, ...

"mainframes" are z/Architecture, not POWER.

I seriously doubt there's a POWER mainframe in the back of Costco to handle the 3 UPC barcode scans per second. It's possible that every Costco store funnels its orders to a single mainframe somewhere.

I think a more realistic case is the visa and MasterCard credit card networks that have almost 0% downtime.

No such thing as a POWER mainframe. IBM's POWER lines (i and p) are different from their mainframe line (z).

Not a POWER Mainframe, no. But AS/400's come in many sizes. The smallest ones are roughly the size of a standard workstation

Back in 1994, they were small enough like a big PC tower, I used to seat on one occasionally, that was out of order.

One of my Summer intern jobs was to run backups every few days on a AS/400 system.

That "seat" was the old one that was yet to be collected.

> Back in 1994, they were small enough like a big PC tower,

Back then their model lineup ranged from the small size like you mention to approx 3 or 4 refrigerator size at the high end.

When I did some system work out at Costco in the 90's they had 4 of the largest models connected together in one system image (sysplex I think).

Indeed, never saw other sizes in real, only on magazine ads.

Just for completionism, two decades back the absolute smallest zSeries was a "rolling box", low and squat, that just barely fit into an office building elevator. Think of a short rack tipped on its side with wheels, but all a single computer. IBM loaned us one to port our Linux software to it. Normal zSeries are like a custom rack to multiple racks, except again all a single computer.

The smallest iSeries I've seen was essentially an "oversize tower PC" form factor.

Mainframes are not POWER, they are z/Architecture.

For AS/400 (IBM i), they're POWER, but come in pretty small models like IBM Power S1012, it's available as "deskside", i.e. a big tower.

I think it's more likely they have a rack of IBM iSeries servers in the back someplace, or maybe in a colo data center.

I can provide some insight into this. Most stores will have a server which handles the barcodes, pricing, etc, locally. Then all transactions are usually sent in a batch everyday from the store server to a central server/servers somewhere for processing, usually around that time reports are also generated and stats made available for BI analysis.

Payments processed by the payment terminals handle the authorization of the payments separately from any store servers, usually through a service such as Connected Payments.