The PCMCIA (PCCARD) Linear FLASH and SRAM technology is indeed deserving of a place in a museum
In its day these two memory technologies were very useful as you can build a computer that has “Run in Place” firmware/software on the memory card. That is to say, the computers boot process does not require the transfer of the operating system or software into RAM before execution. The code is run directly from the memory IC’s on the card. This provided designers with the option to place all of an operating system onto a removable media and not require it to be transferred to Volatile RAM memory. This is often the reason why an embedded computer would contain one of these memory card technologies or would run a software package contained on them as option cards. The two memory technologies are fast enough to make a decent embedded computer, as found in some of my thermal imaging cameras.
The problem for those of us who own equipment that uses Linear FLASH or SRAM cards is that it is a very old standard that has been abandoned in the computing industry long ago. The PCMCIA (PCCARD) format is also long obsolete. This situation means that procuring such memory cards and using them in the modern computing world can present some challenges ! Thankfully there are some suppliers of these vintage technologies who still support Industry as such technology is still to be found in many Industrial equipments of a certain age. There are good explanations of the two memory card technologies and their differing specifications. I shall not repeat those articles here but Google will find plenty of information.
It should be noted that these memory card technologies can present some pitfalls for those new to them. I shall list some below…..
1. Linear FLASH and SRAM cards came in 8 Bit and 16 Bit versions. The correct version is often needed by a host and programming an 8 bit card can be an issue unless appropriate hardware and software from the past is sourced. Some cards offered both 8 bit and 16 bit operation. Most found these days are 16 bit only.
2. Linear FLASH was available as Type 1, Type 2 and Type 5 (3). There was also an Intel “Value” variant that used different (cheaper) memory chips. Some hosts are fussy about which Type they will work with.
3. Linear Flash cards operate from a +5V power supply rail when being read. Many cards require a +12V power supply rail during writes to the card. Some host computers provide the required +12V power rail to the PCMCIA (PCCARD) slot but this was deleted on laptops as time moved on. A laptop that lacks the +12V rail will read these cards but cannot program them unless a hardware modification is made to the laptop. There are PCMCIA (PCCARD) Linear FLASH cards that use only a +5V power supply rail to operate in both the read and write modes. These cards offer compatibility with “5V only” PCMCIA (PCCARD) hosts. If a host needs the 5V only version of Linear FLASH the choice in the current market becomes more limited.
4. There were two main suppliers of memory IC’s for Linear Flash Cards. These were Intel and AMD. Different memory IC’s were used in the cards, often determined by the amount of required memory in the limited amount of space. I personally have not met problems with Intel Linear FLASH cards containing different sizes of memory IC but some hosts may be fussy about the IC brand and capacity ? Intel released a value line of less expensive Linear Flash memory that found its way into the PCMCIA (PCCARD) format. Intel 200 series “Value” cards are an example of such. The cheaper memory was named “StrataFLASH” and used a higher data density to lower production cost per MB. These cards may not play nicely in some host systems.
5. Linear FLASH PCMCIA (PCCARD) cards were available with or without an Attribute (CIS) memory eeprom that was separate from the Linear FLASH memory block. The Attribute memory block contains a digital description of the card and its specifications. This Attribute memory is required by some host computers to identify the memory type that is in its PCMCIA (PCCARD) card slot in order to communicate with it. If the attribute memory is not provided on a Linear FLASH card, the host knows nothing of the cards brand, technology or size until it determines such itself or reads a separate card specification file in the main memory block. As can be seen, the lack of an Attribute memory block can lead to incompatibility with a host system that expects such. SRAM PCMCIA (PCCARD) cards always contain the cards attributes so this is a non issue when selecting SRAM cards.
6. Linear FLASH and SRAM type PCMCIA (PCCARD) cards are not normally interchangeable in an embedded computer host as their firmware expects one or other technology. Laptops are different as they just require the loading of the appropriate drivers fir the desired technology compatibility. Linear FLASH and SRAM PCMCIA (PCCARD) cards are very different to an ATA FLASH card of the same physical format. An ATA card contains a memory controller that meets thecATA memory standards whereas Linear FLASH and SRAM types do not contain a memory controller and may be considered just a pack of raw memory IC’s that are linked to the hosts memory bus. This is one of the reasons why these fast memory cards could be used in a “Run in place” mode of data execution. They may be treated like relatively fast memory IC’s soldered to the hosts motherboard ! An external USB PCMCIA (PCCARD) ATA memory card reader as found on eBay is not compatible with Linear FLASH or SRAM cards unless such is explicitly stated, as in the case of the CSM Omnidrive.
7. SRAM PCMCIA (PCCARD) cards contain SRAM IC’s that require a constant power supply to maintain the data in their memory cells. Loss of power will result in loss or corruption of the data held in the card. For this reason, the cards contain their own internal power source that maintains the power supply to the SRAM IC’s when the host is not providing power or the card has been removed from the host. The technology of the power source is normally a removable Lithium coin cell or a rechargeable button cell. I have not met a card that contained a modern Supercapacitor. The removable Lithium cell versions contain a small capacitor to maintain the SRAM memory supply for around 20 seconds whilst the Lithium cell is changed. With the Lithium coin cell, the cards manufacturer will state a recommended cell changing regime, be it every year, or possibly a longer period. With the rechargeable cells there is higher self discharge and age related degradation to be concerned about.The manufacturer will recommend that the card is powered by a host for a period of time every few months. An elderly rechargeable card may need to have a new rechargeable cell fitted and these cards are not designed to be easily dismantled ! It is important to understand that if a host uses an SRAM technology PCMCIA (PCCARD) for its essential files, these will be lost forever if the cards battery becomes discharged in the absence of host power. This can really ruin your day if you do not have the essential data backed up and a means to program the SRAM card. I own a Spectrophotometer that uses a SRAM PCMCIA card for its operating system and calibration files ! Crazy in my opinion but the unit did come with a PC utility and all the required files to reprogram the card…. Unless, as in my case, the unique floppy disk has become lost over the years ! Fo4 this reason, SRAM PCMCIA card technology can be a poor choice for valuable data that must not be lost. Linear FLASH technology required no power to retain its data fir decades but it is a little slower than SRAM in terms of memory access speeds. Nowhere near as bad as ATA FLASH cards though !
Well that is enough for now. I hope this helps those who are new to these vintage card technologies
Before anyone thinks PCMCIA (PCCARD) technologies are long dead…. Think again. There are many legacy systems still using this elderly technology …. I bought some Linear FLASH cards from a supplier to Airlines fir their Avionics systems ! The cards are used to update onboard Avionics systems that only accept Linear FLASH cards and that would be too expensive to update to ATA standard cards such as Compact FLASH, SDCARD or USB Flash. Industry still uses these legacy technologies in many embedded computer systems that can still be “mission critical”.
Fraser
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