does the generation of a processor affect its speed or its the number of cores?

Question

Am planning to buy a desktop for gaming and recently came across two processors, both are intel core i5, but one is 4th generation and the other one is third generation. These are the models... core i5 4210U and core i5 3570, so to be sure i decided to visit a processor benchmark and do the analysis and the website suggested that the 3rd generation processor is better than the fourth gen processor in almost every feature like speed, gaming, general use and stuff because the third generation processor has 4 cores against four threads while the fourth generation has 2 cores 4 threads. So what really matters when choosing a better processor? generation or number of threads and cores? Thank You

Answer 1

TL;DR: Newer often means better, more cores can mean better but sometimes more cores means less GHz which is often worse for gaming but better for productivity. Ask for build recommendations based on the games you play and the budget you have in the communities linked below.

An answer here will only be able to barely scratch the surface. There are many different properties of a CPU that define what it can do and how fast. In general, a newer generation should have a better single-core performance, but Intel didn't have good improvements within the past couple of generations.

Before going further, I really recommend communities such as /r/buildapc (discord), as there's a lot of people there that have tons of experience in configuring a system based on requirements and budget. Most of the time I'd say the result on there easily reach over 80% of the performance possible for any given budget and even I, after having configured and built over 10 rigs, always post my part-list on there to double-check.

Back on topic: An estimate about single-core performance you can go by is the rate at which it can process instructions. This usually goes from a base value(today that's somewhere around 3GHz) and a boost value, the maximum amount possible during load(somewhere around 4.6GHz for current top models without overclocking). Then there's cache layouts and sizes, a bigger cache usually means a faster CPU, as if it can fetch data from a cache more often, it doesn't have to wait for the slow RAM to provide the required data.

Since CPUs get hot when they work, there's a limit on how tightly you can pack them and how fast you can run them. That's why most high core CPUs(16+ cores) have lower single-core performance, as it can get difficult to avoid overheating. But that doesn't really matter for workloads that can be heavily parallelized. Current games are starting to use multiple cores, but I haven't seen a game yet that'd benefit from having e.g. 12 instead of 4 cores available. Today you usually want to go for 4 or 6 cores(not threads) and high single-core performance(GHz). But most games rely on the GPU much more than on the CPU, so you can also overspend on the CPU and have terrible price/performance if you have no (good) GPU.

Then there's also features, like PCIe4, supported RAM speeds, etc. Going forward I'd either recommend you read up on the subjects of CPU, GPU, RAM, Permanent Storage (HDD/SSD) and their performance indicators(e.g. here or here, Google is your friend :) ), read up on some builds and pre-builts online and try to make sense of the selected parts, look for benchmarks online, configure your system and post your parts list with your budget and games you aim to play.

OR, you skip all that as I recommend in the TL;DR and just post your budget and desired games/workloads and ask for recommendations. Reading up on how to actually assemble a build(takes a routined professional over an hour(see here)), install an operating system, etc. can also take a long time, so if it's your first time doing it, I really recommend letting someone else pick the parts that suit your budget and needs and focus on researching assembly of the system.

EDIT: A few years later and this answer is outdated in several parts already. Keeping it up-to-date seems too much effort, however LTT made an effort to create a long-lasting build-guide; watch it if you want long-lived(ish) recommendations on how to pick and choose parts for your build. Or ask for recommendations in the appropriate forums.