PC Building

This is a consolidation of what I've learnt about building a new computer in July 2022. Nothing fancy, just a helpful reminder of what steps to consider. Some resources are linked to explore.

There are two parts to building a new computer: selecting what to buy, and eventually assembling them. Assembly is the easy part - selecting what to buy may not.

There are many guides out there talking about choosing components, offering pre-build solutions, dispelling myths about building your own PC, etc. Some of these resources I found helpful are linked below.

Logical increments

• Provides recommendations for general usage PCs catering to different budgets
• Parts they recommend are compatible, so is a good reference for parts selection
• CPUs chosen tend towards the latest generation of CPUs
• As of July 2022, their recommended cost distribution (based on 'Outstanding' category) seems to be the following. Note the currently inflated GPU prices. In comparison, my current build has the following distribution. Remember: configure based on your needs!

Reddit - r/buildapc

• Generally helpful recommendations on what components to avoid, and other technical stuff
• Typically reachable when searching for information via Google
• Note that many comments are anecdotes, so there will be occasional conflicting advice - take them with a pinch of salt

Reddit - r/homelab

• Generally more experienced community, with more emphasis on server hardware / networking / Cisco certification, etc.
• Consider reading their fantastic wiki, especially these two articles:
  • Server hardware: https://www.reddit.com/r/homelab/wiki/hardware/
  • Choose what to buy: https://www.reddit.com/r/homelab/wiki/buyingguide/

Bizgram Asia Pte Ltd

• If you live in Singapore, Bizgram is a pretty great wholesaler for computer components and miscellaneous stuff
• Check the regularly updated pricelist to compile costs and availability of components

A plausible decision flow might follow the lines of this.

First consider if you need any of the following:

• High availability / production systems: Strongly consider investing in memory with error-correction capabilities. This limits the type of CPU you can get, e.g. for Intel CPUs, this is only supported by Xeon processors or 12th gen Core processors coupled with W680 chipset.
• Portability: Small cases like mini-ITX are limited mainly by the available PCIe slots and is dependent on whether the case has sufficient clearance. If portability is a priority, either buy a laptop (these are very much custom-built components that would be hard/costly to source and assembly) or do some serious planning for it, e.g. sufficient airflow, low profile GPUs, etc.
• Overclocking: Overclocking is typically done to boost system performance by increasing CPU clock rates. Not only heat dissipation will be a bigger concern, only certain CPU + chipset combinations can perform overclocking.

On form factors - here is a rough comparison between common case sizes by CG Director:

An entire listing of different form factors on Wikipedia.

• ATX: Most popular form for desktops, typically 12x9.6" (width x depth)
• microATX: Popular in desktops and SFF as of 2017, 9.6x9.6"
• Mini-ATX: Designs for mobile on desktop technology, 5.9x5.9"
• Mini-ITX: For thin clients, 6.7x6.7"
• Nano-ITX: For set top boxes, 4.7x4.7"
• Mini PC: e.g. NUC

A short note on mini-ITX, and why it might not be worth the time:

• Problems with mini-ITX builds: https://www.techspot.com/article/2119-everything-about-small-form-factor-pc/
• How to plan a mini-ITX build: https://global.aorus.com/blog-detail.php?i=862
• Examples of mini-ITX cases: SilverStone, NZXT, Cryorig, Dell Z2 Mini

Two key options guiding the form factor to use:

1. Availability of parts for form factor
   • Potential for extension? e.g. to fit a GPU
   • Compatibility between motherboard and components
   • Heat management more critical
2. Portability
   • How easy is it to lug it around / maintain it?
   • Placement in storage / server shed?

Back to the main topic...

The CPU and motherboard tends to go hand-in-hand because the CPU socket tends to change, e.g. for any of the Intel Alder Lake series (12th gen) CPUs, the available chipsets for it are:

• Z690: For enthusiast builds (read: overclocking)
• W680: For performance builds with overclocking and ECC support, see article
• H670: For performance builds without overclocking and ECC support
• Q670: For performance builds without overclocking/ECC support, but retains peripherals, see article
• B660: For general builds, generally starts to have performance cuts
• H610: For budget builds

Motherboards are built around these chipsets, with varying levels of feature support and available footprints.

The rest is really a mix-and-match. See the following description of each component in the subsequent sections. Then finally decide miscellaneous stuff like airflow management / fan placement (note this is more critical when working with smaller builds with limited airflow):

• Power supply:
  • A good resource can be found here: https://forums.tomshardware.com/threads/psu-recommendations-and-power-supply-discussion-thread-toms-hardware.3212332/
• Airflow management:
  • LinusTechTips video on the possible effects of intake.
  • Intake fans on the side and exhaust fans on the bottom. Do not put intakes on top/bottom where dust likely to settle.
  • Dust filters on intake very important.
  • More fans = more dust.
• Noise management:
  • Noise can go for silent components. All or nothing.
  • Avoid water-cooled systems, typically not cost-effective cooling, mainly for aesthetics.
• Remote GUI access:
  • Commercial centralized server connection: Teamviewer, RealVNC
  • Free software client-server connection: TigerVNC, Remote Desktop (RDP), Guacamole

Clock rate:

• The rate at which operations are processed - higher means faster
• The specified clock rate is typically achieved using a lower front-side bus (base) frequency and multiplying using a PLL

Nothing much here - main part described above.

Diagram shows CPU retrieving data via a single memory channel, where data is internally stored in bank group 0, rank 1, of RAM card 2.

This Reddit post is a nice overview of the topics below, consider reading.

DIMM:

• Stands for dual-inline memory module, the physical interface for common memory cards

Channel:

• A single memory channel is typically a 64-bit physical link between CPU and RAM
• Number of memory channels supported is typically limited by CPU, chipset and motherboard
• The number of slots on motherboard does not necessarily correspond to number of memory channels
  • Consumer motherboards tend to allow duplexing of RAM cards per channel

Rank:

• Each memory card can support multiple ranks of 64-bit width each
• A dual-rank memory card has 128-bit width (quad with 256-bit width)
• The memory controller for *each* memory channel can only address a single rank at a time
  • The order in which memory cards are placed in a four-slot, two-channel motherboard is thus critical with only two memory cards - either achieve dual-channel (good) or single-channel (bad)
• A dual-channel dual-rank setup (2 dual-rank cards or 4 single-rank cards) can boost performance by roughly 5-10% compared to dual-channel single-rank setup (2 single-rank cards)
• The number of ranks per memory channel is determined by the motherboard chipset

Bank groups:

• Introduced in DDR4 to multiplex two 8N prefetches in separate memory groups to achieve interleaving
• Typically in memory geometries of x8 (4 bank groups of 4 memory banks) or x16 (2 bank groups of 8 memory banks)
• There is a performance hit if same bank group accessed consecutively
• Inferring from NotebookCheck, a total of 4 memory banks per DIMM is ideal - for single-ranked memory, 1Rx8 performs better than 1Rx16 geometry

CAS latency (CL):

• The fixed number of clock cycles mandated by RAM to return data after a CPU data request instruction

Clock rate:

• The clock frequency at which RAM runs operations - higher means faster operations
• Must be compatible with CPU max memory speed, otherwise RAM will be downclocked
• Typically not overclocked (unless via Intel XMP in motherboard chipset to support non-industry-standard speeds - the CPU specified max memory speed usually only quotes in industry-standard speeds), can be undervolted for longevity/lower power
  • See interpretation in table below
• Modern architecture typically does not directly synchronize to CPU processor clock, but to front-side bus frequency (FSB) / memory controller speeds instead
  • Frequency ratio to FSB can be further tuned using memory dividers when overclocking CPU via increased FSB rate, to avoid a corresponding overclock to RAM for stability
• Access to memory is arbitrated by the memory controller, which internally handles differences in clock speeds using clock domain crossing

First-word latency:

• The real latency of response is determined by the clock rate to CL ratio, typically on order of 10ns
• Typically the shorter, the better. Standard values are generally already in DDR specification

Error-correcting codes (ECC):

• Increases data width by encoding data with parity bits, protects against bit flips in RAM
• Unbuffered vs registered ECC: Registered = more memory at expense of additional middleman register buffer
• Incidence of errors is rare
• Necessary only for production servers where long uptime is required - optional for consumer systems which can tolerate occasional restarts / OS reinstallation, e.g. when kernel issues start occurring due to RAM errors
• May result in higher costs, although prices have generally converged

• For ECC memory, only up to DDR4 available, up to 64 GB sticks for both registered and unbuffered ECC. Average FWL (first word latency) is 14 ns.
• For non-ECC memory, both DDR4 and DDR5 available, up to 32 GB sticks for unbuffered. No market for registered non-ECC memory. Average FWL is 11 ns.
  • Note that DDR5 typically has on-die ECC (separate from true ECC with extra data correction chip), so FWLs are also around 14 ns. Relatively new standard released in 2020.
  • DDR4 memory sticks are most popular at the moment (2022).
• Ranks are typically dual-ranks, to take advantage of rank-interleaving.

1. Choose CPU (and motherboard) based on:
   • Supported memory types, speeds, and capacity
   • Number of DIMM slots available
   • If quad-channel needed
   • If support for ECC memory needed
2. Prefer RAM:
   • Lowest first word latency
   • Two sticks if at least dual-rank, otherwise four single-rank sticks
   • Must be same type of RAM

Shamelessly copied from TomsHardware.

Another great table on bandwidth requirements for displays, as defined by VESA: Resolution vs refresh rate + color-depth -> Required data bandwidth

Notably, DisplayPort 1.4 and HDMI 2.1 support Display Stream Compression 1.2a (DSC), which provides up to 3:1 compression ratio. Note that 8-bit color depth means 24-bit color (8-bit each RGB). Pretty much just get whatever is convenient, e.g. HDMI.

Need to look out for form factors compatible with motherboard / case.

Supplementary power connectors are typically required to supply more power than available through PCIe x16 slot (75W). Extensions seem to be for PCIe and/or PSU.

Graphics card memory (VRAM):

• Internal memory used by GPU
• Read the many GPU buying guides to get a sense of what capacity is recommended

Video ports:

• This article explains the difference between DisplayPort and HDMI
• Need to balance with bandwidth requirements on displays used, see table above

Clock speed:

• Same as that in RAM and CPU

CUDA Cores / Stream Processors:

• No idea at the moment, didn't read it up

FLOPS:

• Floating-point operations per second, maximum theoretical speed
• Useful only when comparing between same architecture

Memory speed/bandwidth:

• Also no idea at the moment

None at the moment, but consider reading these articles:

• Good overview of what GPU matters: https://www.tomshardware.com/reviews/gpu-buying-guide,5844.html
• Nice comparison between different GPUs: https://www.notebookcheck.net/Mobile-Graphics-Cards-Benchmark-List.844.0.html
• General overview of product code designations: https://www.hp.com/us-en/shop/tech-takes/gpu-buying-guide

Distinguish between transfer rate (raw transfer speed) and throughput (actual data rate after encoding, e.g. for 8b/10b encoding, overhead is 20%, so throughput is 80% of transfer rate).

This only a summary - in reality, PCIe/SATA/SAS are specifications for multiple layers, including the physical, link, transport, etc. Read this diagram with a pinch of salt and treat it more like a starting point

Serial buses are preferred over parallel buses due to inherent problems with the latter, most importantly the timing skew (different signal arrival times due to differences in paths/velocities) on order of nanoseconds requires a longer interface clock period, limiting it to sub-GHz performance. On the other hand, serial connections only has a single differential signal in each direction per data lane (reducing timing skew), and the point-to-point serial links between device host and other devices allows for full duplex communication without need for arbitration by the host (needed in parallel configuration since all devices share common set of data and address lines).

Note that you can compare the speed of a storage interface (order of ~1 Gbps) relative to the bus speeds (order of ~50 Gbps), so typically it won't be a huge constraint.

None, but consider reading these articles:

• Nice overview of PCIe: https://www.tomshardware.com/reviews/pcie-definition,5754.html
• Comparison between different storage form factors: https://www.storagereview.com/best_drives

Good as a rough overview of what specifications to consider, but this isn't actually updated. See the list of components purchased updated on PC Part Picker.