[NTLK] Linear Flash Card Questions

[Andrei Chichak]

On 2012-August-23, at 10:21 PM, William Maloney wrote:

> There are quite a few affordable full size, linear flash PCMCIA cards
> available on Ebay - far more than I realized! However, a few
> questions:
> 
> 1.) Do these PC ATA card actually have a tiny ATA Hard drive in them
> or are they linear flash?
> 
First, some background, from your experience with PCs, you probably understand the difference between RAM and disk memory, but do you understand the difference between RAM and ROM? RAM - high speed memory that forgets when you remove the power, mostly silicon flip-flops. ROM - high speed memory that doesn't forget when the power is removed, mostly silicon flip-flops with some capacitors to store the bits forever. Disk - low speed memory that doesn't forget, but it is really big, has motors, arms, magnets, ferrous oxide, platters, processors, amplifiers, and magic, changes magnetic domain changes into bits.

There is a type of ROM memory called EPROM that can be erased and rewritten like RAM, but it doesn't forget when the power is removed. FLASH is a type of EPROM and the biggest difference is that it is erased and written in sectors, blocks of bytes, typically 256 - which happens to correspond to the sector size of … yes, the ATA disk drives.

Now, to your questions:

Do they have tiny ATA hard drives in them?

No, they have a large hunk of FLASH memory and a processor that translates ATA commands into reads, writes, erases, and status calls. To the computer they appear to be a hard drive, but there is no spinning disks, no read/write heads, no motors, and no delay waiting for everything to get into the correct position.

Are they linear flash?
Sort of, at the bottom layer, but they have that processor in the way. Linear flash cards just have a bunch of FLASH chips and they don't understand ATA commands like seek. Just read, write, erase. 

If you were to stick a linear card into a PC, the operating system would send ATA commands to it to get things like the boot sector, partition table, FAT table, and the linear card would sit there and say "DUH". It doesn't talk ATA. For more information, look up the data sheet on a AM29F040B FLASH chip. It's pretty basic stuff, waaaay removed from where normal people tread.

As for your second question about the maximum size, I don't remember.

Andrei