Buying a mainframe - finding and validating

This article is the first part of a comprehensive guide to purchasing a mainframe. While buying new homelab equipment usually requires some research, the amount of work involved in purchasing a mainframe scales with its size. A successful mainframe purchase will take months of research, planning, and administrative work and will generally progress through five stages. They are: Finding a machine to buy, validating that the machine works, shipping the machine, installing the machine, and sourcing peripherals for the machine. Each phase will present unique challenges, but with careful planning, purchasing a mainframe is a manageable challenge. This article will cover the first two of these phases, part two of this series will cover the next two, and part three will cover peripherals.

Finding a machine

Finding a mainframe for sale will require patience. Due to the nature of most mainframe customers, relatively few ever make it to public second-hand markets. Some will show up on government auctions sites like govdeals, publicsurplus, and gsa auctions, but this is still an infrequent occurrence, and these machines often have problems that make them non-viable for hobbyist use. Although it was even rarer, some machines will also get posted to Ebay, and the sellers here will generally be easier to work with (This is where I got my machine). I would also recommend watching mainframe-related mailing lists and forums like IBM-MAIN and the r/mainframe subreddit. Occasionally, people on these lists will give away hardware they are no longer using. Generally, you will find a machine if you wait long enough, but it takes a lot of work.

Validating a machine

If you find a machine, your first instinct will be to rush into the auction or listing, rushing to place a bid before you miss out on the opportunity. This is not advisable for several reasons. Mainframes are immensely complicated machines, and numerous things commonly happen to second-hand machines that can render them permanently nonfunctional. The only thing worse than losing out on a great deal is paying to ship a ton of someone else’s scrap metal.

Broken, missing or wiped SE laptops

This is by far the most common defect that occurs on used machines. Due to mistaken policy, paranoia, or ignorance, many organizations wipe the drives on their SE laptops or remove them entirely. Unfortunately, the firmware on these laptops is unique to each machine and is required to boot and operate the machine. The laptops also include the licensed internal code (LIC) for the machine, which controls the processor speed, and RAM capacity for the machine. Even if you could replace the code on the laptop, the LIC would not match, and the machine would be slowed down to an almost unusable speed.

Luckily, checking to ensure these laptops are present and functional is not too much of a burden for a prospective mainframe owner. On middle-aged machines (z10-z12), the front of these laptops is visible, even when the trays are folded up. If you can see the ThinkPad logo, the computer is still in the machine. On newer machines, the SE is now a rack-mount server mounted on the top of the rack, so you will have to ask for pictures of the server’s drive cages to ensure they have not been removed. With anything older than a z10, you will have to get photos of the laptop cages dropped down to determine if the laptops are still installed. Once you have ensured the laptops are still in the machine, you must take the seller’s word that they have not been wiped. Government sellers, or other first parties, are generally fairly good at providing honest descriptions of the machines they sell. However, you will have to go through a few layers of bureaucracy before you reach someone knowledgeable enough to help. With second-party sellers like you will find on eBay, you must be more careful. Rather than malice, the primary concern is a lack of knowledge. Many companies operate as bulk resellers, buying anything tech related from surplus auctions. These organizations often have minimal knowledge of mainframes and may not know anything about the condition of the item they are selling or have the equipment to power it on. The ThinkPad can be powered on separately from the machine, however, if the seller has a charger. If the seller is unwilling or unable to test the laptops, I would proceed cautiously. I cannot decide whether or not you should proceed, but be aware that the machine may be unusable when you get it.

Old machines

I recommend avoiding purchasing anything before the z10 series. On z10 and later, the Fiber Channel boot feature is included by default. This means that proper FICON/ESCON storage will not be strictly required, and if you can’t find any, you will still be able to use the machine. This concern is alleviated if the machine comes with storage or the seller can boot the machine and verify that FC 9904 is installed. With older machines, software support is also a concern, but not a particularly major one. You will almost certainly never get IBM support, and most features are either supported on z9 and later or only on z13 and newer. A more significant concern is whether you need ESCON support. Most ESCON hardware is only valuable for retro-computing enthusiasts or far outside a hobbyist’s budget. The only items that would be of concern to a hobbyist would be console controller and FlexCUB support. If you want to use physical CRT 3270 consoles, you will need a console controller or an OEC. An OEC will be a better fit for most people, but if you have especially old, unique, or MLT terminals, you will need a physical controller and an ESCON interface. If this is the case, you are limited to z114/z196 or earlier machines.

Processor, memory, and IO configuration

This will generally not be an issue for hobbyists, but it is something that you should still consider before you purchase. Mainframes are generally shipped from the factory fully populated with CPUs and ram. Your machine will still be fully enabled when you get it, however. Most machines come from the factory preconfigured to a lower spec than the maximum using a software limited called LIC configuration control, or LICCC. This will automatically slow down the processors and limit the memory available. All mainframes will have a chart available, dictating the correlation between the three-digit processor speed number and the MIPS and MSU rating of the machine. Ram is also licensed, with the machine restricted to the number of gigabytes specified in the capacity record. Also of note are specialty engines like zIIPs, zAAPs, and IFLs. These are of limited use to hobbyists, but if you want to run Linux on the mainframe (either under z/VM or directly), IFLs will give you a full-speed processor for that Linux workload. Although system speed and memory capacity will generally not be an issue for hobbyists, it is still something to keep in mind when purchasing.

IO cards, like FICON and OSA modules, are not licensed. You can put as many IO and crypto cards in your machine as you can fit. For older model mainframes, you can find IO cards online for a reasonable price, so don’t worry if your system is missing what you want or need. All cards will have a feature code, part number, and Customer Card Identification Number (CCIN). This chart has the reference numbers for all cards that fit into machines from the z9 through z13 series machines. If you need something, just google the CCIN, or put it into eBay, and you will find what you are looking for.


This one is simple. Get pictures. It doesn’t matter where you buy from or how good of a deal you get, get pictures. Even if the seller is not planning to rip you off, they may not know better. Knowing what cards and equipment are in the machine before you buy is a very good idea. You should also be aware of the preinstalled power wiring and the presence of top-exit IO.

Next steps

If you have made it to this point and are still interested in the machine, congratulations! You have found a working mainframe that you can buy and are closer to owning a mainframe than most people will ever be. Don’t rest on your laurels, however. This is the easy part. Join us next time to learn how to book freight shipping on a mainframe, ensure you can house one once it arrives, and wire one to the power grid.