What is hy­per­thread­ing?

The basic idea behind hy­per­thread­ing is to be able to process several threads si­mul­ta­ne­ous­ly with one mi­cro­proces­sor. While pre­vi­ous­ly only one thread could be managed per processor, Intel’s hy­per­thread­ing tech­nol­o­gy now allows a processor to be divided into two logical, virtual cores that process hyper threads si­mul­ta­ne­ous­ly. You can find out how hy­per­thread­ing can improve CPU per­for­mance here.

What may sound like science fiction is nothing more than the old wisdom that four hands can do more than two: hy­per­thread­ing. Intel’s hy­per­thread­ing method orig­i­nates from the server sector, where several physical proces­sors are usually used si­mul­ta­ne­ous­ly to increase computer per­for­mance. With hy­per­thread­ing, on the other hand, there is only one physical processor, but it behaves like two proces­sors. This is made possible by the processor dividing itself into two virtual cores – also known as kernel – which process threads in parallel. This allows multiple in­struc­tion queues to be processed si­mul­ta­ne­ous­ly as a hyper thread, processes to be split between the virtual cores, and CPU uti­liza­tion to be improved.

Hy­per­thread­ing tech­nol­o­gy (HT) is owed to the processor and CPU man­u­fac­tur­er Intel. Private computer users have been enjoying Intel’s hy­per­thread­ing since November 14, 2002. Intel brought its hy­per­thread­ing tech­nol­o­gy onto the market with the Pentium-4 including the Northwood-B core. The successor models, Pentium D and Core-2-Duo, Intel withdrew hy­per­thread­ing again and used dual-core main proces­sors instead.

If you’re hearing about hy­per­thread­ing for the first time, then you may think that every processor should have this tech­nol­o­gy. For­tu­nate­ly, hy­per­thread­ing is active by default in CPU cores, provided they support HT. Nev­er­the­less, hy­per­thread­ing can be turned on and off in the BIOS under “Hyper threading tech­nol­o­gy” via “Enable” and “Disable.” In proces­sors that don’t support hy­per­thread­ing, a physical core only processes several logical processes se­quen­tial­ly, i.e. one after the other. You can check whether hy­per­thread­ing is active or supported in the Device Manager. For example, if you have a computer with two CPU cores, but you see four proces­sors under “Proces­sors,” then hy­per­thread­ing is active.

Probably the biggest advantage of hy­per­thread­ing is that im­ple­ment­ing hy­per­thread­ing tech­nol­o­gy in mi­cro­proces­sors is less expensive than using two physical mi­cro­proces­sors. However, since most computers today already have multi-core proces­sors, this advantage can only be exploited if CPUs with hy­per­thread­ing have the same number of physical proces­sors as machines that don’t support hy­per­thread­ing.

The actual advantage of hy­per­thread­ing is the efficient uti­liza­tion of resources. Two virtual cores in one physical core does not mean that all tasks run at double speed. However, the computing load for several processes can not only be dis­trib­uted se­quen­tial­ly, but also si­mul­ta­ne­ous­ly between the virtual cores. This avoids un­nec­es­sary idle times so that processes can be executed without gaps. Threads don’t have to wait until a com­pu­ta­tion­al­ly intensive thread has been processed, but simply run over the second core.

The advantage of multi-core proces­sors is that a physical core does not have to share its resources. CPUs with ten physical cores, for example, would basically have an advantage over five physical cores with hy­per­thread­ing, because each core can use all available resources to handle processes. Virtual cores, in turn, use the same computing power of the physical cores to manage parallel register sets. Nowadays, it makes sense to work with CPUs with at least two or more physical cores.

Mul­ti­thread­ing and hy­per­thread­ing are very similar at first glance: Both are tasked with ef­fi­cient­ly dis­trib­ut­ing and pro­cess­ing threads in CPU cores. However, hy­per­thread­ing is a sub­cat­e­go­ry of mul­ti­thread­ing and is also called si­mul­ta­ne­ous mul­ti­thread­ing (SMT). To un­der­stand mul­ti­thread­ing, it’s important to know that threads are in­struc­tion queues that are processed dif­fer­ent­ly depending on the hardware and software.

Mul­ti­thread­ing means that multiple in­struc­tion queues are managed si­mul­ta­ne­ous­ly. However, while mul­ti­thread­ing methods such as switch-on event mul­ti­thread­ing and time-slice mul­ti­thread­ing are referred to as pseudo-si­mul­tane­ity, since threads do not run si­mul­ta­ne­ous­ly, si­mul­ta­ne­ous mul­ti­thread­ing, i.e. hy­per­thread­ing, stands for true si­mul­tane­ity in pro­cess­ing. Fur­ther­more, hy­per­thread­ing is a hardware-supported SMT tech­nol­o­gy, while mul­ti­thread­ing can also be supported ex­clu­sive­ly by programs and software.

When it comes to hy­per­thread­ing, the question often arises whether the function really has ad­van­tages compared to multi-core proces­sors without hy­per­thread­ing. The answer is: it depends. For example, it’s crucial what hardware is available and what it’s used for. The fact that hy­per­thread­ing can optimize thread pro­cess­ing through separate pipelines and parallel register sets is un­de­ni­able. For example, the Cray MTA su­per­com­put­er is able to manage an im­pres­sive 128 threads with only one CPU kernel.

Gaming, in par­tic­u­lar, is often noted in con­nec­tion with SMT or hy­per­thread­ing. Gamers in par­tic­u­lar require a lot of computing power when games, music, and maybe even a streamed Twitch recording are running in parallel. Whether hy­per­thread­ing actually improves gaming per­for­mance is debatable. Some gamers say that hy­per­thread­ing actually slows down CPU per­for­mance, while others say that hy­per­thread­ing can be useful when games support four or more cores.