Glossary

Plain-language definitions of the used-server jargon you'll hit while shopping. New to all of this? Start with the beginner's guide.

CPU generation: Roughly when the CPU was made. Older is cheaper but slower and less power-efficient. Xeon E5 v1/v2 (~2012, Sandy/Ivy Bridge) are the cheapest; Xeon Scalable (~2017+) are much faster.
Fit: A 0-100 score of how well a server's hardware matches the use case you picked (cores, RAM, storage, drive bays, quiet, low-power). Tune which specs count with the weight chips; higher means a closer match to what you said you need. Fit answers 'is this the right machine for me?' -- it ignores price. Pair it with Value (fit per dollar) and Deal strength (is the price good vs the market).
Value: A 0-100 score of how much hardware fit you get per dollar. High means lots of capability for the price. It is NOT a market-deal signal -- that's Deal strength; a pricey but loaded box can still score high on Value. Value = Fit divided by price. A cheap under-specced box and an expensive well-specced box can land on the same Value; use Deal strength to tell whether the asking price itself is good.
Deal strength: A 0-100 score of how good the asking price is versus what the model typically sells for, tempered by how much sold-comp data and spec detail back it. 50 is a typical price; higher is a stronger deal. Deal strength is a market signal (is this cheap for what it is?), distinct from Value, which measures hardware fit per dollar. A high Value with a low Deal strength means lots of hardware but priced about right; a high Deal strength means it's underpriced versus recent sold comps. Shown on cards simply as 'Deal'.
Server generation: The chassis family and age (e.g. Dell G13, HP Gen9). Newer generations are generally quieter, more efficient, and take faster CPUs and RAM.
HBA IT Mode: A storage controller flashed to pass drives straight through to the OS. It's what ZFS / TrueNAS / Unraid want, with no hardware RAID in the way. Many servers ship a RAID controller; for software storage you want it in 'IT mode' (a.k.a. HBA / passthrough) so the OS sees each disk directly.
ZFS / TrueNAS / Unraid: Software that pools your drives into one big, resilient storage system (a NAS). They want the disks passed straight through (see HBA IT Mode), not hidden behind hardware RAID. ZFS is a data-integrity-focused filesystem; TrueNAS and Unraid are ready-made NAS operating systems built around it (and similar). All prefer direct disk access + ECC memory.
IOMMU: Hardware support for handing a device (like a GPU) directly to a virtual machine. Needed for Proxmox / ESXi GPU passthrough.
Proxmox / ESXi: Hypervisors -- software that runs several virtual machines on one server. Proxmox is the popular free/open one; ESXi is VMware's. Both can hand a GPU or NIC straight to a VM (see IOMMU). A hypervisor lets one physical server host many isolated VMs (a firewall, a NAS, a game server...). It's the usual first thing a homelabber installs.
ECC: Error-correcting memory that detects and fixes bit errors. Standard on servers and important for NAS / ZFS data integrity.
NVMe-ready: The chassis can take fast NVMe SSDs (via a U.2 backplane), not just SATA / SAS drives.
SFF / LFF drive bays: Bay size: SFF = small form factor (2.5", for SSDs and 2.5" disks); LFF = large form factor (3.5", for big cheap capacity HDDs). A NAS wants LFF bays; a fast all-flash box wants SFF.
SAS: Serial Attached SCSI, the enterprise drive/controller interface. SAS bays also take SATA drives (not vice-versa); it allows more drives per controller and dual-porting for redundancy.
IPMI / iDRAC / iLO / BMC: Out-of-band remote management: a tiny always-on controller (the BMC) that lets you power-cycle, watch the console, and mount an ISO over the network with the OS down. Dell calls it iDRAC, HPE iLO, Supermicro IPMI. Hugely useful for a headless homelab server: you get remote power and a KVM/console without a monitor attached. Some vendors gate the nicest features (like the HTML5 console) behind a license.
Rack units: Height in a 19-inch rack: 1U is about 1.75 inches. A 2U server is twice as tall as a 1U.
Noise tier: How loud the server is at idle, from 1 (whisper-quiet, home-friendly) to 5 (datacenter screamer).
Idle power: Roughly how many watts the server draws doing nothing. Lower is cheaper to run 24/7 at home.
Single-socket capable: A 2-socket board that runs fine with just one CPU installed. Cheaper to buy, lower idle power.
Form factor: Physical shape: rack (mounts in a 19-inch rack), tower (sits on the floor like a PC), or blade.
AVX-512: An advanced CPU instruction set some software (and AI workloads) use; found on newer Xeon Scalable chips.
CXL: Compute Express Link: a newer interconnect (over PCIe) for attaching extra memory or accelerators to the CPU. Only on the latest platforms; niche for a home server today.

Glossary

Plain-language definitions of the used-server jargon you'll hit while shopping. New to all of this? Start with the beginner's guide.

CPU generation

Roughly when the CPU was made. Older is cheaper but slower and less power-efficient. Xeon E5 v1/v2 (~2012, Sandy/Ivy Bridge) are the cheapest; Xeon Scalable (~2017+) are much faster.

Fit

A 0-100 score of how well a server's hardware matches the use case you picked (cores, RAM, storage, drive bays, quiet, low-power). Tune which specs count with the weight chips; higher means a closer match to what you said you need. Fit answers 'is this the right machine for me?' -- it ignores price. Pair it with Value (fit per dollar) and Deal strength (is the price good vs the market).

Value

A 0-100 score of how much hardware fit you get per dollar. High means lots of capability for the price. It is NOT a market-deal signal -- that's Deal strength; a pricey but loaded box can still score high on Value. Value = Fit divided by price. A cheap under-specced box and an expensive well-specced box can land on the same Value; use Deal strength to tell whether the asking price itself is good.

Deal strength

A 0-100 score of how good the asking price is versus what the model typically sells for, tempered by how much sold-comp data and spec detail back it. 50 is a typical price; higher is a stronger deal. Deal strength is a market signal (is this cheap for what it is?), distinct from Value, which measures hardware fit per dollar. A high Value with a low Deal strength means lots of hardware but priced about right; a high Deal strength means it's underpriced versus recent sold comps. Shown on cards simply as 'Deal'.

Server generation

The chassis family and age (e.g. Dell G13, HP Gen9). Newer generations are generally quieter, more efficient, and take faster CPUs and RAM.

HBA IT Mode

A storage controller flashed to pass drives straight through to the OS. It's what ZFS / TrueNAS / Unraid want, with no hardware RAID in the way. Many servers ship a RAID controller; for software storage you want it in 'IT mode' (a.k.a. HBA / passthrough) so the OS sees each disk directly.

ZFS / TrueNAS / Unraid

Software that pools your drives into one big, resilient storage system (a NAS). They want the disks passed straight through (see HBA IT Mode), not hidden behind hardware RAID. ZFS is a data-integrity-focused filesystem; TrueNAS and Unraid are ready-made NAS operating systems built around it (and similar). All prefer direct disk access + ECC memory.

IOMMU

Hardware support for handing a device (like a GPU) directly to a virtual machine. Needed for Proxmox / ESXi GPU passthrough.

Proxmox / ESXi

Hypervisors -- software that runs several virtual machines on one server. Proxmox is the popular free/open one; ESXi is VMware's. Both can hand a GPU or NIC straight to a VM (see IOMMU). A hypervisor lets one physical server host many isolated VMs (a firewall, a NAS, a game server...). It's the usual first thing a homelabber installs.

ECC

Error-correcting memory that detects and fixes bit errors. Standard on servers and important for NAS / ZFS data integrity.

NVMe-ready

The chassis can take fast NVMe SSDs (via a U.2 backplane), not just SATA / SAS drives.

SFF / LFF drive bays

Bay size: SFF = small form factor (2.5", for SSDs and 2.5" disks); LFF = large form factor (3.5", for big cheap capacity HDDs). A NAS wants LFF bays; a fast all-flash box wants SFF.

SAS

Serial Attached SCSI, the enterprise drive/controller interface. SAS bays also take SATA drives (not vice-versa); it allows more drives per controller and dual-porting for redundancy.

IPMI / iDRAC / iLO / BMC

Out-of-band remote management: a tiny always-on controller (the BMC) that lets you power-cycle, watch the console, and mount an ISO over the network with the OS down. Dell calls it iDRAC, HPE iLO, Supermicro IPMI. Hugely useful for a headless homelab server: you get remote power and a KVM/console without a monitor attached. Some vendors gate the nicest features (like the HTML5 console) behind a license.

Rack units

Height in a 19-inch rack: 1U is about 1.75 inches. A 2U server is twice as tall as a 1U.

Noise tier

How loud the server is at idle, from 1 (whisper-quiet, home-friendly) to 5 (datacenter screamer).

Idle power

Roughly how many watts the server draws doing nothing. Lower is cheaper to run 24/7 at home.

Single-socket capable

A 2-socket board that runs fine with just one CPU installed. Cheaper to buy, lower idle power.

Form factor

Physical shape: rack (mounts in a 19-inch rack), tower (sits on the floor like a PC), or blade.

AVX-512

An advanced CPU instruction set some software (and AI workloads) use; found on newer Xeon Scalable chips.

CXL

Compute Express Link: a newer interconnect (over PCIe) for attaching extra memory or accelerators to the CPU. Only on the latest platforms; niche for a home server today.