Introduction
While Desktop CPUs get faster and hotter, somehow the mobile CPUs don’t get the attention they deserve. Mobile CPUs master the careful balance between performance, heat and power consumption. The first on-die second level cache for Intel CPUs were introduced to the mobile market with the Intel Pentium II PE CPU.
There have been new CPU production processes like the .18um debut in the Notebook market. Desktop CPUs lead the prestigious clock race for the fastest CPU, but the quality of the CPU design and ability to produce CPUs with high clock speeds at low voltage clearly show the real potential of a CPU manufacturer.
On the other side is a wide range of different CPU form factors that make upgrading notebooks a nightmare. In this article we will take a look at mobile processors and provide you valuable information about the fascinating world of mobile PCs.
Desktop Thermal
Desktop PCs have space for airflow. 1 to 2 fans along with a power supply fan take care of the heat inside a modern PC. Fast hard drives, plenty of fast-clocked RAM, an insane fast Graphics card and a CPU with a huge cooler are standard in today’s desktop PCs.
In our lab we have CPU cooler with a weight of 400g to take care of the fast CPUs.
The fastest available Desktop Athlon CPU at 1200MHz has a maximum thermal design power of 66W, while the fastest available Desktop Intel Pentium III CPU at 1000MHz has a thermal design power max of 33W.
Thermal Design Power
The thermal design power is the maximum amount of power the thermal solution is required to dissipate. The thermal solution must be designed to dissipate the TDP (thermal design power) without exceeding the maximum Tjunction specification.
CPU vendors provide the values TDPmax and TDPtyp to the designers.
TDPmax represents the total power dissipation of the processor while executing a worst-case instruction mix at nominal voltages and normal operating conditions.
You can also calculate the TDPmax with the following equation, if the CPU vendor does not want to provide the higher TDPmax:
TDPmax = Vcccore max * Icccore
TDPtyp represents the power dissipation of the processor while executing publicly available software at nominal voltages and normal operating conditions.
TDPmax > TDPtyp
Tjunction
The Intel Pentium III processors incorporate an on-die diode that monitors the die temperature (junction temperature). Modern Desktop Pentium III Motherboards monitor this thermal diode of the CPU.
This Tip is only for the very crazy people among us (Note: At your own Risk!):
Make sure that your Pentium III Motherboard monitors the thermal diode of the CPU. Enter the Motherboard BIOS and go to the Hardware Monitor Setup. Lift the CPU fan a bit and you can monitor the CPU temperature rise within seconds, until the Motherboard BIOS enters the ACPI modus or the CPU shuts itself down. In most cases the Motherboard BIOS enters the ACPI mode (hangs up the system) to prevent further damage to the CPU.
Don’t do this with AMD Athlon CPUs! AMD Athlon CPUs do not have this feature inside the CPU. If your fan stops, is not mounted correctly or if it is not pressed to the CPU very tightly, your CPU will get fried within seconds beyond recovery!
When the junction temperature reaches 135 °C, the Pentium III processor will stop executing all instructions. This is signaled to the system with the THERMTRIP# (Thermal trip) signal. The processor will remain stopped until RESET# goes active via Restart or Reset-Switch.
The goal of every thermal design must be to dissipate TDPmax and avoid reaching Tjunction with a safe margin.
Desktop processors
As a representative of the Desktop CPUs, I will take a closer look at the Intel Pentium III processors. Usually when a CPU is being reviewed, we take a look only at the Benchmark results. If the processor gets unstable, we increase the Vcc of the CPU a bit to get the CPU stable. With the increase of the voltage the heat dissipation of the CPU is also increased. That is part of the reason why huge coolers are so popular.
In a desktop PC this is easy. You have space inside of the system for huge coolers, and when the ambient temperature near the CPU gets too high, you get yourself an additional cooler to provide a decent airflow around the CPU-cooler.
Lets take a look at the Pentium III CPUs and its TDPmax and Tjunction.
The TDPmax of the 1133 B MHz CPU is the theoretical value, since Intel had to withdraw its CPU from the market after our publication of its defects. The main reason for the huge TDPmax of the 1133 B MHz CPU is related to the fact that Intel used the good old overclocker trick to increase Vcc of the CPU from 1.70V to 1.80V.
As described earlier, with an increased voltage you need to take much more care of TDPmax and Tjunction. To make matters worse, Intel decreased Tjunction to 62°C. This requires higher efforts to keep the CPU cool.
For all the AMD fans out there, the AMD Athlon require also massive cooling. At 1133MHz the Athlon has a TDPmax of 63W and a Tjunction of 95°C.
On the positive side, Desktop CPUs are widely available and up to 300 US$ cheaper then a mobile CPU.
Cooling a Mobile CPU
With limitations in height, weight and space the cooling of a notebook is a huge challenge.
The most traditional way to keep things cool is a heat sink with a fan. But where should it be placed? When you place the fan in the middle of the notebook, the fan will push the heated air from the heat sink to the other components in the system like the HDD or Battery.
That leaves no other option but to mount the fan near the edge of the case. This way it can get fresh cold air in and push the hot air out.
When the fan is at the edge of the system where do you place the CPU?
When the CPU is directly underneath the fan, then the thickness of the system will increase. But no one is willing to accept a bulky notebook nowadays. To keep the system slim, there are several tricks to spread the heat from the CPU.
Heat Pipes, Heat Sinks, Heat Spreaders and Remote Heat Exchange
Heat sinks don’t need to be big and bulky, like those everyone is used to from desktop CPUs. The heat of the CPU must be transferred away from the CPU. A heat sink must have a big surface to transfer the heat.
There is only limited space inside the notebook. You need space for battery, drives like HDD and CD-ROM, PCMCIA, power supply and charger board.
Why not use the biggest space available. Place a heat spreader underneath the Keyboard. Now you say, “wait a minute, I will burn my fingers”. No, you won’t. A notebook keyboard is about 28×11 cm and this is a big surface.
Sample of a heat spreader with a heat sink and heat pipe
Heat Pipes, Heat Sinks, Heat Spreaders and Remote Heat Exchange, Continued
The ambient temperature is about 25°C and the body temperature is 37°C. When the heat sink gets about 40°C you will not be disturbed and the thermal envelop improved 15°C. Removing 15°C would require a very big fan with it’s power consumption and noise.
The next thing with such a big heat spreader is to get the heat of the CPU that is only at one small spot inside of the notebook across the whole heat spreader.
First, get a thermal attach material between the CPU and a small heat sink. Attached to the heat sink is a heat pipe that transfers the heat away from the heat sink across the heat spreader.
There are many designs for heat pipes available. One Version uses a semi-hollow metal pipe that contains water. The phase changing mechanism of water provides an efficient way of transporting heat from the heat sink across the heat spreader or to a Remote Heat Exchange.
A Remote Heat Exchange is a finned structure for the maximum surface and an adjacent fan that forces ambient air through the system and the RHE (Remote Heat Exchange).
If the case of a notebook is made out of a magnesium alloy, then this case can be used as a heat spreader too.
Desktop vs. Mobile CPU
This one is hard to explain, because there are so many different mobile CPUs.
First, the Tjunction of the mobile CPUs is important. The Intel Mobile CPUs have a Tjunction of 100°C. When you compare it to the Tjunction of the Desktop CPU you might think, hey it’s only a 20°C difference! But remember that the heat spreader under your keyboard and the fan has to get rid off that additional 20°C. This will make a hot notebook or at least a very loud one, because the fan will be running most of the time. You might have saved some bucks with the purchase, but now you’ve got the loudest notebook around.
Speedstep
The mobile Pentium III introduced 100MHz front side bus and Speedstep technology to the notebook market.
Speedstep technology automatically detects whether the mobile PC is using AC power or battery. When the notebook is using AC Power, the CPU will run at full speed.
In battery mode the CPU will reduce its clock speed and core voltage. By doing this the CPU will consume less power.
Speedstep | |||||
AC-Mode | Battery-Mode | Vcccore/V AC-Mode | Vcccore/V Battery-Mode | TDPmax/W AC-Mode | TDPmax/W Battery-Mode |
600 MHz | 500 MHz | 1,60 | 1,35 | 20,0 | 12,2 |
650 MHz | 500 MHz | 1,60 | 1,35 | 21,5 | 12,2 |
700 MHz | 550 MHz | 1,60 | 1,35 | 23,0 | 13,2 |
750 MHz | 600 MHz | 1,60 | 1,35 | 24,6 | 14,4 |
800 MHz | 650 MHz | 1,60 | 1,35 | 25,9 | 15,1 |
850 MHz | 700 MHz | 1,60 | 1,35 | 27,5 | 16,1 |
How does it work? Changing the voltage and the clock-multiplier usually requires a reboot with a regular CPU. The clock multiplier register is only being set during start-up of the processor. A Speedstep Controller at the mobile module or the Notebook Motherboard can detect the power mode change. The Operating System (Windows 98/ME/2000) defines the new state to the controller and puts the CPU into sleep. The Speedstep Controller adjusts the voltage regulator and changes the CPU multiplier. After those changes the Controller forces the CPU out of sleep. All of this takes less then 1ms.
Speedstep, Continued
Unfortunately we didn’t have all those CPUs for testing. I used my Notebook for benchmarking and compared a Pentium III with fixed Speed against a Pentium III Speedstep processor.
ASUS L8400B Notebook 14″ Display, 192MB SDRAM, Windows 98SE, Battery Mark 4.0
The Conditioning Test is a worst-case instruction mix without pauses, while the Life Test represents a more regular user test with some pauses between the instructions.
Battery Mark 4.0 | ||
Conditioning Test/min | Life Test/min | |
750 MHz Speedstep CPU | 88 | 143 |
600 MHz Speedstep CPU | 114 | 156 |
500 MHz Fixed CPU | 105 | 154 |
The above table shows very direct that a Speedstep Pentium III CPU running with 600 MHz in Battery Mode can beat a non Speedstep Pentium III CPU running with 500 MHz. Both CPUs are being produced in .18um process.
Some Users might say: I paid for 750 MHz and I also want to run 750 MHz in Battery mode.
Intel has got a small program just for this. You can select the running mode by software.
Default setting of the Speedstep program running in Battery-Mode
A small Flag in the Windows Task Bar indicates the running Mode. The above picture shows the battery mode and the below picture the AC-Mode.
Speedstep program running in AC-Mode
Please make sure that this program is installed with your Speedstep CPU. It will provide you valuable battery time. If your CPU does not support Speedstep, the program will not be present in the taskbar.
Speedstep is only one step to better management of the CPU time. The next feature is the virtually unknown QuickStart. Intel QuickStart automatically reduces power to less than 0.5W when the processor is not being used. The processor can enter and exit the low power state between keystrokes.
In Deep Sleep mode the processor consumes much less power, but it takes much longer time to speed the CPU up to max performance or battery mode.
AMD offers a similar technology called PowerNow for its mobile K6-2+ and mobile K6-III+ CPUs.
Transmetas technology for saving battery time is being called Longrun.
So lets jump into the world of the mobile CPUs.
Mobile Module 1
This module is much more than just a CPU. The Intel Mobile Module contains CPU, Northbridge, L2 Cache and voltage regulator.
Intel introduced these mobile modules with the Pentium Processor including MMX and TX Chipset.
Later Intel upgraded the MMC-1 (Mobile Module Connector 1) to a Pentium II Processor with additional level two cache and BX Chipset.
Some users like Tom have been able to upgrade their notebook from a Pentium to a Pentium II in a snap. The Notebook itself had the Southbridge and all the peripheral chips like VGA Card, Sound Card, PCMCIA Controller, Charger, etc mounted on the Notebook-Motherboard.
Shut down the Notebook, replace the Pentium MMC-1 with the Pentium II MMC-1 or the Celeron MMC-1 and start with a new processor family.
While the TX Chipset of the Pentium MMC-1 Module supported both SDRAM and EDO Memory, the BX Chipset of the Pentium II / Celeron MMC-1 Module supported only SDRAM.
But there were some negative sides to that. The costs for the Mobile Modules were very high, because the module included the Chipset and all the other components.
Mobile Module 1, Continued
MMC-1 Top View
MMC-1 connector-view CPU with on-die L2 cache
MMC-1 connector-view, CPU with external L2 Cache
MMC-1 chip-view after removal Thermal Transfer Plate
The MMC-1 Connector has 4 rows and a total of 280 pins.
With the Connector between the MMC-1 Board and the Motherboard of the Notebook the total height of the system was limited. You were not able to build a very slim notebook.
What I personally didn’t like about the MMC Modules were the three screws. The very crucial connection between the Notebook Motherboard and the MMC Module is secured by only 1 screw while the other two screws are at the less important side of the module. When times gets tough with the notebook, there is a slight chance that the connection gets lost and your notebook won’t start.
If you have such a notebook and want to upgrade it, you should check with your vendor for the TDPmax of the system and the BIOS.
Mobile Module 1, Continued
All of the above CPUs run at the same Voltage of 1.6V. The big advantage of 2.4W was achieved by using on-die level two cache in comparison to discrete level two cache chips.
Those Pentium II processors with on-die level two cache, using the ‘Dixon’-core, are officially called Pentium II PE. PE stands for performance enhanced. The discrete 512kB level two cache of the Pentium II processor is clocked with half the speed of the CPU core, while the 256kB on-die cache of the Pentium II PE processor runs at CPU clock.
The Celeron at MMC-1 started right away with 128kB on-die level two cache.
This is no error. The Celeron processor was available at higher clock rates then the Pentium II processor. You can clearly see the reason for this in the above chart. The good old overclocker tip: increase the voltage and it will run faster. However, the processor also got much hotter too.
Mobile Module 2
While the MMC-1 Module used a PCI Interface to connect to the Notebook Motherboard the MMC-2 (Mobile Module Connector 2) used an AGP/PCI Interface.
MMC-2 Connector View
The MMC-2 has 10 rows and 400 pins. It is not possible to use an MMC-1 Module in an MMC-2 slot or vice versa. The BX chipset used with the mobile modules always supports AGP, but the connector of the MMC-1 doesn’t allow it’s use. The MMC-2 processors kicked-off AGP graphics inside of a notebook for 3D graphics and better DVD playback.
Like the Pentium II MMC-1 Module the Pentium II MMC-2 module uses 1.6V.
Also the advantage of the on-die cache is obvious. On-die level two cache not only reduces the weight of the module by ~4g, but also saves valuable power.
The MMC-2 Celeron is a bridge to the next step in the evolution of mobile CPUs.
Mobile Module 2, Continued
The Pentium III was introduced some time after the Desktop Pentium III to the mobile market with the MMC-2.
Not only had the CPU core changed, but also the front side bus – from 66MHz to 100MHz. With that front side bus change, the upgrade path was partially cut. The new Pentium III processors used a memory clock of 100MHz, while the connector to the Notebook Motherboard remained the same.
After the initial introduction of the first fixed clock mobile Pentium III processors, Intel added the Speedstep feature to its higher clocked mobile CPUs.
The Speedstep controller at the MMC-2 module needs also some support from the Notebook motherboard. You must check with your notebook vendor if your notebook can support that feature.
Mini-Cartridge
Parallel to the MMC-1 module a different form factor for mobiles CPUs arrived to the market. The Mini-Cartridge was one of the first Intel processors to implement the on-die level two cache.
When you see the above chart you might stop for a second and ask yourself, why is the 400 PE MHz CPU as hot as the 366 PE MHz CPU? The answer to this is quite strange. While all Mini-Cartridges use 1.6V, the 400 PE MHz CPU only requires 1.55V.
Inside the Mini-Cartridge is the CPU core with cache and thermal diode and sensor.
Mini-Cartridge, Continued
The Mini-Cartridge Connector has 8 rows with a total of 240 pins.
Most of those cartridges had been used in combination with the BX chipset as shown above.
BGA-1
The market for notebooks demanded slim and light notebooks. The mobile processors like the MMC-1, MMC-2 and the Mini-Cartridge presented so far all required plenty of space. Also the height of the mating connector and the module are about 10mm. When you want to build a notebook with a total height including case, display and motherboard of less then 3 cm you have to start looking for a different CPU connector solution.
With the on-die level two cache there is no need for an additional PCB like the MMC-1 or MMC-2.
BGA-1 CPU top view
BGA-1 CPU bottom view
When the CPU is mounted, the height of the BGA-1 processor is only between ~ 2.5mm, about a quarter of a mounted MMC-1 or MMC-2 module height.
BGA-1, Continued
As the name of the processor suggests, the CPU is a BGA processor. BGA is short for ball grid array for surface mount.
Another advantage of those BGA1 processors is the availability of low voltage CPUs. A very slim notebook has restrictions in height and surface that lead to a bad thermal dissipation. It is required to decrease the voltage in order to reduce the TDPmax.
The mobile Celeron 400MHz processor is the hottest BGA1 CPU.
If you have such a BGA1 processor in your notebook, you will not be able to upgrade it because it is soldered to the notebook motherboard.
Micro-PGA1
The height advantage of the BGA-1 processor and the production advantage of a socket processor have been combined in the Micro-PGA1 processor.
The BGA processor is mounted on top of a small PCB with attached pins. The height of the mounted processor increases to ~3.5 mm plus 1.25mm for the pins.
Micro-PGA1 CPU top view
Micro-PGA1 CPU bottom view
When a processor is being soldered directly to the PCB, the notebook vendor loses flexibility to react to new processor prices. Notebooks are usually shipped from the notebook maker to the notebook vendor as a bare bone. A notebook bare bone comes without HDD, processor and only onboard RAM. When the CPU price changes while the notebook is on its way from the production site to the final kitting site, the customer requests a different specification. With the barebones that are in stock, the notebook vendor needs flexibility to order production with little stock risk due to processor price change.
Micro-PGA1, Continued
One disadvantage of the CPU is that you need to change some jumpers to adjust the clock multiplier. This is the first and last time you will hear something about jumpers in combination with mobile processors. All the other processors with sockets are auto detected by the system.
Like the BGA1 processor the Micro-PGA1 CPU was used in slim notebooks.
Strange but true – the mobile Celeron processor is the fastest Mirco-PGA1 CPU. Before you try to get one to upgrade your notebook, you have to check with your notebook vendor about the TDPmax. The increase of the TDPmax cannot be neglected.
BGA-2
To bring the mobile Pentium III to a wider audience and reduce the costs of the MMC-2 Module, the BGA-2 was introduced to the market.
100MHz front side bus, auto detection of the clock multiplier and the Speedstep technology plus the other Pentium III features is only a small list of its features.
BGA-2 CPU top view
BGA-2 CPU bottom view
No other mobile Intel CPU offers such a wide range of low voltage and high-speed processors. When Intel is battling Transmeta for the low power CPU, they will use the 600-500 LV MHz CPU. In AC-Mode the CPU runs with as little as 1.35V and in battery-mode only with 1.1V.
Like the BGA-1 processors the BGA-2 CPUs will only be available soldered on to the notebook motherboard.
Micro-PGA2
The Micro-PGA2 CPU is my current favorite mobile processor.
Differences between Micro-PGA1 and Micro-PGA2 are:
Micro-PGA | ||
Micro-PGA1 | Micro-PGA2 | |
total pins | 615 | 495 |
VID-pins | 0 | 5 |
front side bus | 66MHz 100MHz |
66MHz 100MHz 133MHz |
Not connected pins | 243 | 24 |
size | ~36 x 32mm | ~34 x 28mm |
The number of pins is equal to the number of balls with the BGA processors.
Micro-PGA2 CPU top view
Micro-PGA2 CPU bottom view
Most all-in-one notebooks use the Micro-PGA2 processor.
BGA-2, Continued
Unlike the BGA2 processors the Micro-PGA2 CPUs are not available in low voltage version.
When you compare the mobile Pentium III with the mobile Celeron at 100MHz the TDPmax is quite similar. While a desktop Celeron is limited to only 66MHz front side bus, the mobile Celeron at BGA-2 and Micro-PGA2 is running with 100MHz front side bus.
This clearly shows that the limitation of the desktop Celeron to 66MHz is not related to any technical difficulties.
Why is the Micro-PGA2 CPU may favorite? It’s easily upgradeable!
Mobile CPU Matrix
After all those different CPU form factors you might want to storm into the next Radio Shack and try to get a new CPU for your notebook.
- Please check what kind of CPU is inside of your notebook.
- Please check with your notebook vendor for the TDPmax of your Notebook.
- Please check our Mobile CPU Matrix to find the right CPU for your socket.
Conclusion
Mobile CPUs sometimes lead technology, with the 100 MHz front side bus of mobile Celeron processors or with the introduction of new manufacturing processes like the .18um process and the on-die level two cache starting with Pentium II.
Mobile CPUs follow technology with the front side bus of 100MHz with mobile Pentium III processors or the late introduction of Pentium III to the mobile market.
Notebooks are complete PCs with a weight less then 4kg.
You can have a desktop replacement with a 850MHz Pentium III or a thin and light notebook weighing less then 2kg and a low voltage 500MHz Pentium III.
Within certain limits you can upgrade the CPU of your notebook. But you will not be able to upgrade the notebook motherboard if you want to support a complete new range of CPUs.
Every board inside of a notebook is custom made for that notebook model. Upgrading a Pentium II with TDPmax 11.5W to a Pentium III with TDPmax 27.5W requires much more then just a motherboard change.
There are only very few standards for a notebook design. The notebook motherboards are being designed around the devices like battery, HDD, FDD and DVD/CD-ROM. Every bit of space is being used to squeeze in the chips and to provide the best thermal support.
But all of this will be material for several follow-up articles. So, stay tuned for the new section of tom’s hardware guide – the mobile guide.