PC card (PCMCIA) details

Many friends who use laptops often come into contact with PC cards (previously called PCMICA cards, and now this name has been simplified). Such games, indeed, generally have one or two PC cards in the computer that notebook users face each day. Slots are of course very familiar, but now that PC cards are of use everywhere on the desktop, it is necessary to introduce you to the knowledge about PCMCIA and to unveil her mystery.

The history of PCMCIA:

With the development in recent years, PCMICA has newly defined specifications such as CardBus and Zoomed Video in the increasingly urgent demand for the development of high-speed applications such as Mpeg multimedia and 100M high-speed Ethernet. Of course, PCMCIA is not limited to these speed improvements. At the same time, it has made significant improvements in low power consumption features such as device compatibility and 3.3V operating power supply specifically for mobile processing.
Today, PCMICA not only promotes the ability to work collaboratively in the field of portable computers, but also in various aspects such as digital cameras, cable TV, set-top boxes and even cars. With the increasing demand for modular peripherals between different products, PCMCIA has recently described its mission as: developing standards for modular peripherals and making them accepted worldwide.
One of PCMCIA's new tasks is in establishing standards for small-sized plug-in cards. SmartMedia cards widely used in many handheld devices are also proposed and formulated by PCMCIA.

The first glimpse of PC card technology In the early 1990s, the rapidly developing mobile computer industry drove the simultaneous development of lighter, smaller, and more portable information processing tools. One of the most exciting of all these improvements is the PC card technology. PC card has now become an important part of mobile computer technology.

TYPE I cards, with a thickness of 3.3mm, are mostly used in early memory cards, such as RAM / SRAM cards, Flash cards, OTP cards, etc .;
TYPE II card, with a thickness of 5.0mm, is mainly used in I / O devices, such as LAN Ethernet card / Modem and some large-capacity external storage devices;
The TYPE III card has a thickness of 10.8mm. The most common type of this card type product is a small PC card hard disk, that is, a temperature-type hard disk and a corresponding ATA controller are integrated in this 10.8mm thick space.

PC card technology outlook In recent years, with the development of special integrated circuits, surface assembly, multi-layer PCBs and micro-machines, many devices that have only had enough space on TYPE II cards or even TYPE III cards have appeared before. It is integrated on the TYPE I / II card. The most typical example is that the 5GB PC card hard disk produced by TOSHIBA is TYPE II, and the capacity has reached more than 10 times that of the previous TYPE III PC card hard disk made by VIPER. This is the trend of thinner and thinner PC cards. With the development of modern micro-mechanical technology, high-density magnetic recording and GMR heads, PC card hard drives with larger capacity, lighter weight and lower energy consumption will be born.
Low energy consumption: In recent years, the power consumption of new integrated circuits has become smaller and smaller, coupled with the power management of the system, the PC card controller, and the thermal management of the PC card itself, it has played a certain role in alleviating the increasingly serious heat dissipation of the notebook. .
Multiple functions are integrated into one card: the integration of ICs in PC cards continues to improve, and it is no longer difficult to build in multiple control circuits at the same time, and the 2IN1 cards of network cards and MODEM are no longer new. You can imagine what it looks like if a PC card has all the interfaces-it's still the size of a credit card ...
New interface: With the popularity of gigabit networks entering desktops or other high-speed interconnection methods, when the bandwidth of the CardBus interface is not enough, a revolution in interface specifications is coming.

Card version

A variety of bus operation methods can be implemented on the CardBus interface. Among them, the bus control operation method can allow the system CPU to reduce the work intensity and reduce the task requirements of the CPU on the system bus. This is a very important factor for improving the efficiency of today's multitasking operating systems.
The CardBus interface not only supports existing PC card audio digital waveforms, but also adds support for pulse width modulation (PWM). Through the cooperation of the software, you can get a greater improvement in audio quality than the previous standard.
In terms of electrical indicators, CardBus' signal protocol is derived from the PCI interface, but there are still differences between the two. The following is a comparison of some performance indicators between the two:

The CardBus interface works in a 32-bit digital mode at a frequency of 33Mhz, so that the interface can provide high bandwidth up to 32bits / 8 * 33Mhz = 133MB / s, which makes the PC card in some high bandwidth (100M network card And IEEE1394, etc.) or real-time data / video acquisition and other applications can still be at ease. So the 100M EtherLan PC card, FireWire interface PC card and USB2.0PC card that are currently on the market are almost all CardBus interface cards.

DMA support in the PC card standard.

DMA can bring a considerable performance improvement to the computer system. From the above comparison, we can see that because the DMA transfer is used, the CPU can save the state information of the interruption site without spending additional instruction cycles (usually these tasks cost a few Instruction cycle), thereby increasing execution efficiency and speeding up.
DMA can also reduce the cost of peripheral products. The period from when the peripheral issues an interrupt request to when it starts to output data is called the interrupt delay. If the peripheral is a data source like a floppy disk, an Ethernet card, or a digital video stream, the interrupt delay will cause the data to be untimely. Outflow, to solve this problem can only use the cache on the peripherals, and the increased cost of the cache and the need for additional integrated on-board / on-chip cache controllers are not conducive to reducing the cost of the device. The DMA device only takes a very short time The data is sent out in near real time, so it can be used with little or no cache, which has a considerable advantage in production.

The connection between DMA and CardBus in PC card

CardBus provides a wider and more informative bandwidth to communicate with the CPU, and it also allows peripherals to be called bus controllers. Specifically, it allows peripherals to directly control the system bus without going through the DMA controller, so that the peripherals can have more freedom in where and how to transfer data. Of course, this increase in freedom has to pay a certain extra cost, because the CradBus peripheral usually requires more circuits than the DMA peripheral to implement the bus control configuration.

The debate about which interface is more popular, DMA or CardBus, is still continuing. As a minor change to the previous PC card standard, DMA is easier to be accepted by manufacturers and software designers, and CardBus may be difficult to adopt because it can be said to be a major reform in the PC card standard; some CardBus support The author believes that all PC cards will appear in the future with a high-performance CardBus interface, and DMA supporters believe that the acceptance of CardBus is slower than expected and if DMA has a long life cycle. However, the current situation in the market is that each of them has certain application areas.
Another important factor is cost. In the PC market, which is very sensitive to cost, the lower price usually wins. Therefore, how the relatively high-cost CardBus card can compete with the DMA in court is very important for the future development of CardBus. Everyone remembers the battle between Rambus and DDR.