Last Updated: 2023-02-21


Traditional server:

  • CPU + DRAM + PCIe connecting local peripherals (NIC, SSD, GPU, TPU).

Future servers:

  • New security considerations including bare metal support and many independent control domains.
  • Limited chip bandwidth for Coherence + DRAM.
  • Emergence of CXL.
  • Tighter coupling between accelerators and general purpose compute.
  • Memory wall landing requiring more tiering (L4 cache, slower memory).

Server racks

  • 1 unit (1U) = 18 inches (480 mm) x 1.75 inches (44mm).
  • The most common form-factor: 42U.

Blade Server vs Rack Server vs Tower Server

  • blade server => blade chasis => rack
  • rack server => rack
  • tower server (stand alone)

Blade Server: a stripped-down server computer with a modular design optimized to minimize the use of physical space and energy.

Blade server popularity declined due to virtualization.

Largest Brands

  • Dell EMC: R740 PowerEdge
  • HPE: DL360 (1U), DL380 (2U)
  • Inspur (浪潮集团)
  • Lenovo

Baseboard Management Controller (BMC)

TL;DR: for remote server management.

A specialized processor for remote monitoring and management of a host system (a computer, network server or other hardware device).

Usually an ARM-based SoC (System on Chip) with graphics and control logic built in.

Accessed remotely either via a dedicated or shared network connection, and has multiple connections to the host system, giving it an ability to monitor hardware via sensors, flash BIOS/ UEFI firmware, give console access via serial or physical / virtual KVM, power cycle the host, and log events.

Allows a system administrator to perform many different monitoring and management tasks remotely without having to be physically located next to and connected to the system. All modern servers and other devices used in a data center (such as switches, storage devices, power supply devices etc.) now have a BMC.

Protocol: Redfish.

Brand specific:

  • HPE: iLO, Integrated Lights-Out
  • Dell: iDRAC, Integrated Dell Remote Access Controller


HPE iLO (Integrated Lights-Out): a proprietary embedded server management technology by HPE;

  • provides out-of-band management facilities
  • The physical connection is an Ethernet port that can be found on most ProLiant servers
  • makes it possible to perform activities on an HP server from a remote location.
  • The iLO card has a separate network connection (and its own IP address) to which one can connect via HTTPS.
  • power up, reset, mount
  • The iLO firmware emulates the BMC functionality.