The CPU

Chapter 4 — The CPU

The CPU is the brain of the build — every instruction your code executes, every SSH session you open, every Docker container compiling in the background, every X2GO frame arriving over VPN is processed here. For a development workstation, the CPU choice has more impact on daily feel than any other component. A fast CPU makes compiling quick, IDE indexing snappy, and ten simultaneous tasks manageable. A weak one makes all of those painful.

What we're replacing: Your Intel Core i5-10400 (LGA1200, 6 cores / 12 threads, 4.3GHz max) is a solid older chip but belongs to a dead platform. The LGA1200 socket is gone — no new boards support it, no new CPUs will ever fit it. This chapter selects its replacement, and settles the "i5 vs i7, Intel vs AMD" question for your specific workload.

What a CPU Does

The CPU (Central Processing Unit) executes instructions — sequences of operations like add, compare, branch, and store — at extraordinary speed. Everything that happens on your computer is ultimately a stream of such instructions passing through the CPU. For a development workstation, the CPU is stressed by:

Compilation — converting source code to binaries; naturally parallel, benefits strongly from more cores
IDE background indexing — IntelliJ, VS Code, PyCharm continuously analyse and index your project while you type
Docker and containerisation — each container can pin a core; more containers = more cores needed
Remote desktop decoding — X2GO and RDP decode compressed video streams; sustained CPU load per active session
Virtual machines — each VM gets its own vCPU allocation
Database processes — local PostgreSQL, MySQL, Redis all consume CPU when queries run
Browser + dev tools — Chrome with many dev tabs, Postman, Fiddler — all CPU consumers

Unlike gaming (which favours single-core clock speed), development workloads are a mix: some tasks (interactive typing, browser, IDE UI) favour single-core speed, while others (compilation, Docker builds, parallel test runs) reward many cores. The sweet spot for a dev machine is high IPC with a good core count — not the raw MHz number.

Understanding the Specs

Core Count

e.g. 16 cores

Physical processing units. Each core can run an independent task. More cores = more things happening simultaneously without competition. Critical for dev workloads where compilation, Docker, IDE, and remote sessions all run at once.

Thread Count

e.g. 24 threads

With Intel Hyperthreading (or AMD SMT), each physical core presents two logical threads to the OS. Useful for lightly-threaded tasks. Core count matters more; thread count is a secondary benefit.

P-cores vs E-cores

Hybrid architecture (Intel 12th/13th gen)

Intel's 12th and 13th gen CPUs have two core types: Performance cores (P-cores) for demanding single-threaded work, and Efficient cores (E-cores) for background tasks. Windows 11 automatically routes work to the right core type. Explained in detail below.

Base Clock / Boost Clock

e.g. 3.4 GHz / 5.4 GHz

Base clock is the guaranteed minimum frequency. Boost clock is the peak single-core speed under light load. For sustained all-core work (compilation), the CPU runs below boost — real-world all-core speed is between base and boost. Clock speed alone does not determine performance — IPC matters equally.

IPC (Instructions Per Clock)

Architecture-dependent

How much work gets done per clock cycle. Intel 12th/13th gen ("Alder Lake" / "Raptor Lake") delivered a major IPC jump over 10th/11th gen. Your old i5-10400 at 4.3GHz will lose to an i7-13700K at the same clock because of IPC — newer architecture = more work per tick.

TDP — PL1 / PL2

e.g. 125W (PL1) / 253W (PL2)

TDP (Thermal Design Power) is the base power limit (PL1). PL2 is the burst power limit Intel allows for short periods before throttling back to PL1. Your PSU and cooler must handle PL2 peaks, but sustained load runs at PL1. On a B760 board at defaults, the CPU respects Intel's spec limits — not boards with "enhanced" power profiles.

Cache (L1 / L2 / L3)

e.g. 30MB L3

Ultra-fast on-chip memory the CPU uses to avoid fetching data from RAM. L3 cache (the largest, shared between all cores) is particularly important: more L3 means less time waiting for RAM. This is why the AMD Ryzen 7800X3D (with 96MB 3D V-Cache) is exceptional for gaming — but for compilation, L3 is less decisive than core count and clock speed.

Socket Compatibility

Must match motherboard exactly

Intel LGA1700 CPUs fit only LGA1700 motherboards. AMD AM5 CPUs fit only AM5 motherboards. There is no cross-compatibility. The socket also locks in which chipsets are supported — confirmed in Chapter 3.

Integrated Graphics

Intel UHD 770 (most 13th gen)

A graphics chip built into the CPU die. On Intel 13th gen, most models include one (the "F" suffix variants remove it). Not used when a discrete GPU (your RTX 3050) is installed, but useful as a fallback for diagnostics if the GPU ever fails.

Intel's Hybrid Architecture — P-cores and E-cores

Starting with 12th gen (Alder Lake), Intel moved to a hybrid CPU design that combines two very different core types on the same chip. This directly affects how your development workload is handled:

Intel Core i7-13700K — Die Layout (simplified) ┌─────────────────────────────────────────────────────────┐ │ P0 P1 P2 P3 P4 P5 P6 P7 │ E0 E1 E2 E3 │ │ ─────────────────────────────── │ ──────────── E4 E5 │ │ 8 Performance Cores │ E6 E7 │ │ Hyperthreaded → 16 threads │ 8 Efficient Cores │ │ High clock, high IPC │ No HT → 8 threads │ │ Up to 5.4 GHz boost │ Lower power, lower clock │ ├─────────────────────────────────────────────────────────┤ │ Shared L3 Cache (30MB) │ ├─────────────────────────────────────────────────────────┤ │ Intel Thread Director ← Windows 11 │ │ routes tasks to the right core type automatically │ └─────────────────────────────────────────────────────────┘ Example: you are typing in IntelliJ (P-core handles UI) while a Gradle build runs in background (E-cores handle it) and an SSH session streams data (E-core handles low-load task)

What this means for your workload:

IDE, browser, interactive tasks → automatically scheduled on P-cores for maximum responsiveness
Compilation, Docker build, test runner → spread across all cores (P + E) for maximum throughput
Background X2GO / RDP stream decoding → E-cores absorb this without competing with your foreground work
Requires Windows 11 for Intel Thread Director support — Windows 10 does not route correctly and wastes E-core potential

More cores, not just faster cores: The i7-13700K has 16 cores total (8P + 8E) vs your current i5-10400's 6 cores. Running three simultaneous remote sessions plus an IDE plus a Docker build was forcing your CPU to context-switch aggressively. With 16 cores it can hand each task its own core with headroom to spare.

The Intel 14th Gen Warning

Avoid Intel 14th gen K-series (14600K, 14700K, 14900K) for a new build in 2025. These chips have documented instability issues that caused reports of permanent CPU degradation across many builds — particularly the i9-14900K and i7-14700K. The root cause was boards applying excessively high voltages and power limits beyond Intel's official spec. Intel released a microcode update (0x12B) in August 2024 to address the worst cases, but it does not recover CPUs already damaged, and not all boards apply it correctly. For a reliable development machine that you're investing £200–350 into, this is a real risk not worth taking. The 13th gen i7-13700K performs virtually identically and does not have these issues at spec power limits on a B760 board.

Intel 13th Gen — The Lineup for Your Build

CPU	P-cores	E-cores	Threads	Boost	L3 Cache	TDP (PL1)	Price (est.)	Verdict
i5-13400	6	4	16	4.6GHz	20MB	65W	£160–190	Strong value, but fewer cores than ideal for heavy dev multitasking
i5-13600K	6	8	20	5.1GHz	24MB	125W	£220–260	Strong budget pick — excellent IPC, good core count
i7-13700K ★	8	8	24	5.4GHz	30MB	125W	£280–340	Top pick — best balance of multi-thread power and value
i9-13900K	8	16	32	5.8GHz	36MB	125W / 253W MTP	£420–500	Overkill; high TDP, significantly more expensive for marginal dev gain

Head-to-Head: The Final Candidates

SocketLGA1700

Cores / Threads16C (8P+8E) / 24T

Base / Boost clock3.4 / 5.4 GHz

L3 Cache30MB

TDP (PL1 / PL2)125W / 253W

iGPUIntel UHD 770

DDR4 supportYes (with DDR4 board)

DDR5 supportYes (with DDR5 board)

£280 – £340

The 8 P-cores handle your 3 concurrent remote sessions plus IDE without any of them competing. The 8 E-cores absorb compilation, Docker, background tasks. 30MB L3 is the largest in the 13th gen mid-range. This is the CPU that will make you forget your current machine ever felt slow. Well within PSU headroom at 125W sustained on a B760 board.

SocketLGA1700

Cores / Threads14C (6P+8E) / 20T

Base / Boost clock3.5 / 5.1 GHz

L3 Cache24MB

TDP (PL1 / PL2)125W / 181W

iGPUIntel UHD 770

DDR4 / DDR5Both supported

£220 – £260

Saves ~£60–80 vs the i7. 14 cores is still a massive leap from your current 6. The 2-fewer P-cores do show under sustained heavy multitasking — if you regularly have Docker builds + full IDE + 3 remote sessions all pegged simultaneously, the i7 headroom is meaningful. For lighter multitasking, the i5-13600K is excellent value.

SocketAM5 (new board + DDR5)

Cores / Threads8C / 16T (no hybrid)

Base / Boost clock4.5 / 5.4 GHz

L3 Cache32MB

TDP105W

iGPUNo (7700X) — 7700 has one

RAMDDR5 only

£230 – £280

Strong single-core speed, great Linux/WSL compatibility, lower TDP. The 8 cores are all full performance cores with SMT — different from Intel's hybrid model. Fewer total threads than the i7-13700K for the same price, but well-regarded platform with long AM5 roadmap. Good choice if you prefer AMD or plan more Ryzen-optimised workloads.

SocketAM5 (new board + DDR5)

Cores / Threads12C / 24T

Base / Boost clock4.7 / 5.6 GHz

L3 Cache64MB

TDP170W

iGPUNo

RAMDDR5 only

£290 – £360

12 full-performance cores at high clocks with a massive 64MB L3 cache. The most i7-13700K-comparable AMD option. The 170W TDP is notably higher than the Ryzen 7 7700X and demands a capable cooler. If going AM5 and wanting genuine competition with the i7-13700K in multi-threaded dev work, this is the chip to evaluate.

PSU note — i7-13700K and your TX550M 550W: Under full all-core stress the i7-13700K hits ~180W sustained on a B760 board with PL1 set to 125W (the board's long-term power limit is respected but the PL2 burst window drives it higher briefly). Add the RTX 3050 LP at ~80W, drives, fans — your 550W PSU is operating at approximately 65–70% load under sustained peak, which is fine and actually near the ideal efficiency zone for an 80+ Gold unit. You do not need to replace the PSU for this CPU.

What to Look For (and Avoid)

8+ total cores for a heavy dev workstation
Current-gen architecture (13th gen Intel or Ryzen 7000+)
High boost clock (5.0GHz+) for single-thread responsiveness
Confirmed socket match to your chosen motherboard
Good IPC for the generation (check benchmarks vs your i5-10400)
Reasonable TDP for your cooler budget
K-suffix Intel = unlocked, but runs at spec on B-series boards — not a problem
iGPU present — useful diagnostic fallback
Brand-new, sealed box from reputable seller

Intel 14th gen K-series (documented voltage/degradation issues)
Any LGA1200 CPU (dead platform — same socket as your i5-10400)
Any LGA1700 CPU below i5 tier (Celeron/Pentium for a dev machine is painful)
Used / pulled CPUs without warranty
i9-13900K unless you have a real use case — TDP is high and gains for dev are marginal
Paying a premium for an F-suffix (no iGPU) when the non-F is similarly priced
Cheap cooler bundles if buying a K-suffix — K CPUs don't include a stock cooler
Mismatched socket to motherboard — always double-check both are LGA1700

Your Existing CPU — Intel Core i5-10400

Specification	i5-10400	i7-13700K (new)	Difference
Socket	LGA1200 (dead)	LGA1700 (current)	New platform with upgrade path
Architecture	Comet Lake (2020)	Raptor Lake (2022)	~30-40% more IPC per clock
Total cores	6 cores	16 cores	2.7× more cores
Threads	12	24	2× more threads
Max boost clock	4.3 GHz	5.4 GHz	+25% single-core clock
L3 cache	12MB	30MB	2.5× more cache
DDR5 support	No	Yes	Future-proof RAM path
PCIe generation	PCIe 3.0	PCIe 5.0	NVMe Gen 4/5 storage
Integrated graphics	UHD 630	UHD 770	Better iGPU fallback
Verdict	Replace — combined IPC + core count improvement makes this one of the most impactful upgrades you can make

Installing the CPU

K-suffix CPUs do not include a cooler in the box. The i7-13700K ships as CPU only — no cooler, no thermal paste (some thermal paste is pre-applied to many coolers). You will need a separate LGA1700-compatible CPU cooler (covered in Chapter 5). Do not power on the system without a cooler installed — a CPU without cooling will hit thermal limits and power off within seconds.

Prepare the board on a flat, non-conductive surface

With the motherboard out of the case and on its anti-static bag, locate the CPU socket. Remove the black plastic protective cover by lifting the socket retention arm — it will pop off. Keep this cover in case you ever need to transport the board without a CPU installed.

The LGA1700 socket has 1,700 delicate pins on the motherboard side (unlike AMD where the pins are on the CPU). A bent motherboard pin typically means an RMA. Never touch the socket contact area, never drop the CPU into the socket, and never force anything.

Lift the retention arm and load plate

Push down slightly on the retention lever to disengage the hook, then swing it out and up. The metal load plate will lift as well. You'll see the empty socket with its grid of contacts exposed. This is the position for CPU installation.

Align and place the CPU

Hold the CPU by its edges — never touch the gold contact pads on the underside. Look for the small golden triangle marker in one corner of the CPU package. Match this to the triangle marked on the corner of the socket. The CPU also has two notches on its sides that align with tabs in the socket for a single orientation. Lower the CPU straight down — it should fall into place under gravity with zero force.

If the CPU doesn't drop in, it's oriented incorrectly — rotate 180° and try again. A properly aligned CPU seats with no pressure at all.

Close the load plate and secure the retention arm

Lower the metal load plate over the CPU, then push the retention arm down and hook it back under the catch. This requires moderate force — the arm is designed to apply even clamping pressure to the CPU. You will hear a click when it fully engages. The CPU is now secure.

The arm will feel stiff — this is normal. Do not be tentative; if it's not fully clicked under the hook, it will appear closed but won't make reliable contact. Apply firm, steady downward pressure on the arm near the hook end.

Apply thermal paste (if your cooler requires it)

Many coolers (especially tower coolers like the NH-D15 or Dark Rock Pro 5) come with thermal paste pre-applied to the base. If the cooler has a pre-applied patch of grey compound, you can mount directly — no separate paste needed. If the cooler base is bare metal, apply thermal paste to the centre of the CPU lid before mounting. See the thermal paste section below for the correct method.

Remove the pre-applied paste protective film (if any) before mounting. It's transparent and easy to miss, but leaving it on will give catastrophically high temperatures.

Thermal Paste — Application Methods

Thermal paste fills the microscopic gaps between the CPU lid and the cooler base, dramatically improving heat transfer. Too little = air pockets = high temps. Too much = overflow onto the socket = potentially catastrophic. The right amount applied correctly produces optimal results.

╔═════╗ ║ ║ ║ ● ║ ← pea-sized ║ ║ centre dot ╚═════╝

Centre Dot Method

✓ Recommended

╔═════╗ ║ ║ ║ ─── ║ ← thin line ║ ║ across centre ╚═════╝

Thin Line Method

✓ Also works well

╔═════╗ ║▓▓▓▓▓║ ║▓▓▓▓▓║ ← spreading ║▓▓▓▓▓║ manually ╚═════╝

Spread Method

✗ Can trap air bubbles

╔═════╗ ║ ●● ║ ║ ● ║ ← too much ║ ● ●║ will squeeze out ╚═════╝

Too Much

✗ Risk of socket contamination

Aim for a pea-sized amount (3–4mm diameter) in the centre of the CPU lid
The cooler mounting pressure spreads it evenly across the die area
Most thermal pastes (Noctua NT-H1, Arctic MX-4, Thermal Grizzly Kryonaut) perform similarly — avoid cheap "silver" paste or generic included tubes from unknown cooler brands
After first boot, retighten cooler mounting screws after the paste has settled (some pastes spread slightly with heat — covered in Chapter 5)

Testing the CPU

POST and BIOS identification: On first boot, enter BIOS (Delete or F2) and confirm the CPU is correctly identified by name and core count. The BIOS will display e.g. "Intel Core i7-13700K @ 3.40GHz" and should show 24 logical processors. If it shows the wrong CPU or 0 cores, reseat the CPU (turn off, unplug, reopen socket).

CPU-Z — full identification: Download and run CPU-Z (free). The CPU tab should show: Name: Intel Core i7-13700K, Cores: 16, Threads: 24, Technology: 10nm, Core speed boosting above 3.4GHz under load. The Caches tab should show L3 = 30.0 MBytes.

HWMonitor — idle temperatures: Download HWMonitor (free) and check CPU temperatures at idle (desktop, no load). All cores should be below 45°C at idle in a reasonably ventilated case. If idle temps are above 60°C, the cooler is not seated correctly or thermal paste was applied incorrectly — remount before stress testing.

Prime95 stress test (Small FFTs — 10 minutes): Download Prime95 (free) and run "Small FFTs" for 10 minutes with HWMonitor open alongside. This is a worst-case load. Acceptable results: CPU temperature stays below 90°C on all cores, no throttling occurs (clock speeds remain consistent), no errors reported. If temperatures exceed 95°C, the cooler is not performing adequately — check mounting and thermal paste.

Cinebench R23 — benchmark score: Download Cinebench R23 (free) and run both Single Core and Multi Core tests. Expected scores for i7-13700K: Single ~2,000+, Multi ~30,000+. Compare to published results online — a significantly lower score suggests thermal throttling or incorrect power limit settings in BIOS.

Verify BIOS power limits: In BIOS, check that the CPU is not running beyond Intel's specified PL1 (125W) without your explicit instruction. Some boards ship with "Performance Mode" or "Multi-Core Enhancement" enabled by default, which removes power limits and can push 13th gen CPUs toward the same conditions that caused 14th gen issues. On a B760 board, set the CPU to operate at Intel Default Settings if this option is available.

Real-world dev test: Once the OS is installed, run a compilation of a large project (e.g. checkout a large open-source codebase and run a full build) while simultaneously opening your IDE and an X2GO session. The system should remain responsive throughout — if it feels sluggish or the build takes longer than expected, check for throttling in HWMonitor during the run.

Reuse vs Replace Summary

Component	Keep or Replace	Reason
i5-10400	Replace	LGA1200 — incompatible with all current platforms. No resale value against a new socket.
Intel Core i7-13700K	Buy new	Best fit for your workload — 16 cores, 5.4GHz boost, 30MB L3, confirmed B760 compatible
i5-13600K alternative	Buy new (if budget)	Saves ~£60–80. 14 cores is still a massive improvement. Consider if other budget areas are tighter

Next: Type PC5 to generate Chapter 5 — CPU Cooling, where we'll select the right tower cooler for the i7-13700K, covering LGA1700 mounting hardware, cooler height clearance, and validating temperatures under load.