Nbsp;   CPU Trends

In the past, CPU speeds used to increase with time, so an application that ran slowly on one machine would typically run faster on a newer machine. However, CPU manufacturers are unable to continue the trend of making CPUs faster. When you run CPUs at high speeds, they produce a lot of heat

that has to be dissipated. A few years ago, I acquired a newly released notebook computer from a respected manufacturer. This computer had a bug in its firmware that made it not turn the fan on enough; as a result, after running the computer for a while, the CPU and the motherboard melted. The hardware manufacturer replaced the machine and then “improved” the firmware by making the fan run more frequently. Unfortunately, this had the effect of draining the battery faster, because fans consume a lot of power.

These are the kinds of problems that the hardware vendors face today. Because CPU manufactur- ers can’t continuously produce higher-speed CPUs, they have instead turned their attention to mak- ing transistors smaller so that more of them can reside on a single chip. Today, we can have a single silicon chip that contains two or more CPU cores. The result is that our software only gets faster if we write our software to use the multiple cores. How do we do this? We use threads in an intelligent fashion.

Computers use three kinds of multi-CPU technologies today:

■ Multiple CPUsSome computers just have multiple CPUs in them. That is, the motherboard has multiple sockets on it, with each socket containing a CPU. Because the motherboard must be bigger, the computer case is bigger as well, and sometimes these machines have multiple power supplies in them due to the additional power drain. These kinds of computers have been around for a few decades, but they are not as popular today due to their increased size and cost.

■ Hyperthreaded chipsThis technology (owned by Intel) allows a single chip to look like two chips. The chip contains two sets of architectural states, such as CPU registers, but the chip has only one set of execution resources. To Windows, this looks like there are two CPUs in the machine, so Windows schedules two threads concurrently. However, the chip only executes one of the threads at a time. When one thread pauses due to a cache miss, branch mispredic- tion, or data dependency, the chip switches to the other thread. This all happens in hardware, and Windows doesn’t know that it is happening; Windows believes that both threads are run- ning concurrently. Windows does know about hyperthreaded CPUs, and if you have multiple hyperthreaded CPUs in a single machine, Windows will first schedule one thread on each CPU so that the threads are truly running concurrently and then schedule other threads on the already-busy CPUs. Intel claims that a hyperthreaded CPU can improve performance by 10 percent to 30 percent.

■ Multi-core chipsA few years ago, single chips containing multiple CPU cores have entered the scene. As I write this, chips with two, three, and four cores are readily available. Even my notebook computer has two cores in it; our mobile phones now have multiple cores in them too. Intel has even been working on a single chip with 80 cores on it! Wow, this is a lot of com- puting power! And Intel even has hyperthreaded multi-core chips.

Date: 2016-03-03; view: 737